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Winter/Spring 2024

Tues. January 9: Jennifer West (DRAO), in person Recording

Progress on understanding the Galactic magnetic field
The pursuit of understanding the structure and origin of the Milky Way’s magnetic field is a central science question driving several radio polarization surveys, including the Polarization Sky Survey of the Universe’s Magnetism (POSSUM) from the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, the VLA Sky Survey, and The Global Magneto-Ionic Medium Survey (GMIMS). These surveys are poised to give us an unprecedented view of the polarized radio sky. I will give an overview of the expected science, status of progress we have made towards unraveling the answers to these questions, and discuss strategies for the management and analysis these massive datasets.

Tues. January 16: Trystyn Berg (DAO), in person

Astrophysics in absorption — exploring galaxy evolution with quasar absorption lines
Quasar absorption line systems are excellent probes of chemical enrichment across time. In particular, absorption line systems tracing the interstellar (ISM) and circumgalactic media (CGM) of galaxies are ideal environments for both measuring chemical enrichment and constraining the baryon cycle within galaxies. Furthermore, detailed comparison of abundance patterns to observed stellar abundances and predicted yields can provide insights into the progenitor stellar populations that made up these galaxies. In this talk, I will first highlight how the metal enrichment of galactic gas reservoirs provides a key constraint on feedback processes using data from the XQ-100 survey. Using these results to identify where to look for the most metal-poor environments, I will then shift to more detailed chemical abundances studies of the most metal-poor gas reservoirs in order to pinpoint the properties of the first stars to form in the Universe. I will then conclude with what the future holds for pushing our knowledge of chemical enrichment with quasar absorbers.

Tues. January 23: Chris Mann (DAO), in person Recording

TESS exoplanet candidate follow-up with ground- and space-based instruments 
The Transiting Exoplanet Survey Satellite (TESS) mission has done a fantastic job of discovering exoplanets over the last few years by detecting the small drop in stellar brightness as a planet passes between us and the star (i.e. a transit).  Not only has it found many thousands of candidates, it has focused on bright and nearby targets that are well suited for detailed spectroscopic follow-up.  However, every one of these candidate exoplanets requires follow-up observations to rule out false positives and constrain physical and orbital parameters.  This huge effort is coordinated by the TESS Follow-up Observing Program (TFOP), a collection of professional and amateur researchers and telescope operators around the world.  
Posing a particular challenge, are the “long-period” TESS candidates (~100+ days) that show few or singular transits in the TESS data.  Without accurate period information, further characterization of the system grinds to a halt.  This is unfortunate, as these “temperate” exoplanets can provide unique insight on atmospheric structures and processes.  My Ph.D. research involved contributing to the general TFOP effort, and also providing dedicated follow-up effort on some of these challenging long-period targets.

Tues. January 30: Paul Ripoche (UBC), in person Recording

Insight into the faint galactic white-dwarf population: calibration tools for future deep synoptic surveys
In addition to studying galaxies and the early Universe, future deep synoptic surveys will be essential to our understanding of the structure and history of the Milky Way (MW) by providing unprecedented data on the faint galactic stellar populations. However, observing stars at unrivalled depths presents challenges in identification and calibration.
Using the unprecedented 27.1-mag median depth of the Canada-France-Hawai‘i Telescope Large Area U-band Deep Survey (CLAUDS), we precisely studied the galactic stellar populations among over 15 billion of astronomical objects, over 20 square degrees.
In the absence of parallax measurements in the CLAUDS data, we devised photometric methods relying solely on colours to select stars in a survey designed to observe galaxies. We demonstrated the usefulness of precise measurements in determining properties of foreground stars, particularly white dwarfs (WDs).
Furthermore, through the analysis of WDs in the CLAUDS data, we developed a powerful technique for reducing systematics in synoptic surveys, such as the Legacy Survey of Space and Time (LSST). This technique could significantly enhance data quality in future deep synoptic surveys.

Tues. February 6: Ryley Hill (UBC), in person Recording

Resolving the cosmic infrared background with JWST and ALMA
I will talk about combining archival ALMA data targeting the Hubble Ultra Deep Field to produce the deepest currently attainable 1-mm map of this key region. 45 galaxies are detected, 39 of which have JWST counterparts. A stacking analysis on the positions of about 2000 ALMA-undetected JWST galaxies yields a surprising amount of additional information – I will talk about the fraction of the cosmic infrared background resolved by JWST and ALMA, and argue that essentially all of the galaxies that contribute to the cosmic infrared background have now been accounted for.

Tues. February 13: Vincent Chambouleyron (UCSC), in person (not recorded)

Tues. February 20: Kristine Spekkens (RMC), in person Recording

Gas-Rich Galaxies as Cosmological Probes
The atomic gas (HI) content of nearby galaxies provides important insight into how they form and evolve within the standard cosmology. In this talk, I will highlight some of my group’s recent progress towards building statistical samples of gas-rich galaxies to use as cosmological probes. I will first focus on how sensitive HI searches in optically-selected dwarf satellite galaxy candidates are a powerful tool for measuring their structure and constraining formation models. I will then describe how the widefield WALLABY survey, now underway on the Australian SKA Pathfinder (ASKAP), is delivering the first spatially-resolved populations of HI disks for comparison with cosmological predictions. This work paves the way for probing HI disks across cosmic time using the SKA when it comes online towards the end of this decade.

Tues. February 27: Lisa Kewley (CfA Harvard), in person (no recording)

A new vision for the Center for Astrophysics | Harvard & Smithsonian
I will present the latest discoveries and developments at the Center for Astrophysics | Harvard & Smithsonian (CfA).  Our discoveries cover solar astrophysics, star formation and evolution, galaxy formation & evolution, extrasolar planets, black holes, and cosmology.  I will describe the latest ground and space-based technological developments at the CfA, including new space satellites, and compelling new instrumentation for current and future ground-based telescopes in the optical, infrared, IR, and X-rays, as well as for climate science.  I will discuss our challenges with Petabyte scale datasets and the application of AI to astronomical problems.  Finally, I will provide an overview of the diversity, inclusion and culture initiatives that are being implemented at the CfA, using evidence-based studies from the literature.

Tues. March 5: Matt Taylor (Calgary), in person Recording

Do Massive Black Holes Come in Small Packages? The Search for Central Black Holes in Low-mass Stellar Systems.
The black hole (BH) mass function in the local universe is a fundamental measure of the origin and growth of BHs over Cosmic time. Specifically, the occupation fraction of massive black holes in low-mass stellar systems such as dwarf galaxies is an important ingredient for competing theories on supermassive BH (SMBH) formation. Observational challenges limit available avenues to search for BHs in dwarfs, but one under-utilized strategy is to infer the presence of central BHs by their dynamical influence on the cores of compact stellar systems (CSSs) including nuclear star clusters, ultra-compact dwarf galaxies (UCDs), and compact elliptical galaxies. CSSs have interconnected (often galactic) formation histories, and this technique has recently been successful in detecting SMBHs in several nearby UCDs, thereby proving their galactic origins as the remnant nuclei of former dwarf galaxies tidally stripped of their outer stellar sheaths. With the launch of JWST a systematic census of BHs in CSSs is possible, as similar studies are prohibitively expensive using current ground or space-based facilities. We are capitalizing on JWST’s capabilities by using NIRSpec+IFU to obtain spatially resolved stellar kinematics of 18 carefully selected CSSs crossing nearly four decades in mass, all located in a single galaxy cluster environment (Virgo). In this talk, I will give an overview of these efforts including primary science aims and preliminary results based on JWST Cycle 1 operations.

Tues. March 12: Sarah Tuttle (Washington), in person Recording

Here Be Dragons: Exploring the galaxy/CGM interface through data and instrumental adventures
The circumgalactic medium has gone from barely an idea to a crucial part of our understanding of the regulatory galactic environment in about 20 years. I will present a variety of projects and approaches that my group is using to gain an understanding of the evolution of galaxies. We will start with some unusual local galaxies that seem to be quenching, and the steps we’ve taken to try to determine the source of that regulated star formation. We will explore HETDEX and in particular several projects exploring extended emission from Lyman Alpha emitters. And we’ll wrap up by discussing a proposed UV cubesat called Maratus where we are attempting to map the CGM in the FUV at relatively large scales, and some discussion about what comes next on larger scales in the UV from the US. 

Tues. March 19: Marta Reina-Campos (McMaster), in person (no recording)

Beacons in the sky: star clusters from UNIONS and JWST
Stellar clusters are found in virtually all galaxies in the Local Universe, and the JWST is quickly revealing them also at different cosmic epochs. The high-surface brightness of these gravitationally-bound stellar systems makes them excellent beacons across galactic environments, revealing the underlying distribution of mass around their host galaxy. In this talk, I will discuss the demographics of massive star cluster populations both in the Local Universe from the UNIONS survey, and located 3 Gyr in the past from public JWST data. I will discuss our selection procedure of massive clusters in elliptical galaxies within the UNIONS dataset, and show preliminary results of their luminosity, colour and radial distributions. I will also review recent results on the star cluster population in the galaxy cluster Abell 2744, and I will end by discussing how we are correlating these detailed observations with the distribution of mass around this cluster. 

Tues. March 26: Kristy McQuinn (Rutgers), virtual (no recording)

Resolved Stellar Populations Studies with the Hubble and James Webb Space Telescopes
The study of resolved stellar populations in nearby galaxies was transformed by the high sensitivity and spatial resolution of the Hubble Space Telescope (HST), and is now being transformed again with the more powerful James Webb Space Telescope (JWST). The results have far-reaching impacts ranging from providing the most detailed and quantitative measures of the star formation histories of low-mass galaxies and insights into their growth across cosmic timescales, to determining precise distances to galaxies throughout the Local Volume which place galaxy properties on an absolute scale and are essential inputs for measuring of the local value of the Hubble Constant.
In this talk, I will (i) highlight recent results from resolved star studies on very low-mass galaxies with HST data, (ii) present the first star formation history of a galaxy with JWST data alongside a comparison to HST data of the same field, and (iii) introduce new tip of the giant branch (TRGB) distance calibrations derived from HST infrared data and JWST data on nearby galaxies, the latter of which paves the way for a JWST-based measure of the Hubble Constant.
I’ll also provide highlights on the upcoming Nancy Grace Roman Space Telescope.

Tues. April 9: Siddarth Mishra-Sharma (MIT / CCA) virtual Recording

Illuminating the Dark Universe with Probabilistic Machine Learning
The coming years will witness an influx of astrophysical data that will enable us to map out the distribution of matter in the Universe, image billions of stars and galaxies, and create maps of the Milky Way to unprecedented precision. These observations will contain significant potential for challenging our current picture of cosmology and particle physics, e.g. regarding the nature of dark matter. At the same time, the complexity of the data and underlying physical models will present novel challenges. Showcasing applications to a range of different systems (e.g., dwarf galaxies, gravitational lenses, and large-scale structure), I will describe how maximizing the scientific return of astrophysical observations towards fundamental physics discovery will require a qualitative shift in how we interact with the data, centering machine learning as a powerful discovery tool, and an interdisciplinary approach intersecting the particle physics, astrophysics, and machine learning communities.

Tues. April 16: Rowan Smith (U St. Andrews), virtual (no recording)

How galactic environment alters molecular clouds and star formation.
Star forming clouds are not islands in and of themselves, but instead form out of, and are embedded within the ISM of our Milky Way galaxy. Large scale galactic structure such as spiral arms, and clustered supernovae feedback from previous generations of star formation drive large scale turbulence which influences fragmentation within the cloud. Differential rotation within the disc stretches out large filaments of HI, within which molecular filaments are embedded. Magnetic fields generated by the large-scale dynamo thread the galaxy and influence the alignment of filamentary clouds and how they fragment. In this talk I use the CLOUDFACTORY simulation suite of Smith et al. 2020 and its follow-ups to investigate how these factors affect how stars form in galaxies. The CLOUDFACTORY simulations are ideal for this task as they model the large-scale disc (20 kpc) of galaxy, but also go down to extremely high resolution in individual clouds (0.1pc’s) down to the scale of individual star forming cores. Using this we can investigate whether star formation is a purely local process or whether the wider galactic environment alters the efficiency, timescales, and clustering of star formation.

Tues. April 23: William Thompson (NRC HAA), in person (no recording)

Orbit modelling to detect exoplanets
To study exoplanets outside our solar system, we have at our disposal an ever-increasing smorgasbord of techniques. These range from the well-known transit and radial velocity methods, to the up-and-coming direct imaging, GAIA-Hipparcos absolute astrometry, and interferometry methods. Increasingly, these techniques are overlapping in sensitivity, allowing us to detect the same planet using two, or even three different kinds of data.
I will discuss some challenges and opportunities found by combining these disparate kinds of data and present results on several exciting exoplanets: HR 8799, 51 Eri b, Epsilon Eridani b, and more. I will further discuss how this kind of multi-technique modelling is powering three next generation direct imaging surveys, guiding our observations towards the most promising targets. 

Tues. April 30: Daniel Gilman (UToronto), virtual Recording

A guided tour of dark matter physics with quadruply-imaged quasars
The existence of dark matter explains astrophysical phenomena from sub-galactic length and mass scales to the properties of the CMB and large-scale structure. However, we lack a detailed understanding of the particle properties of dark matter, such as its mass, formation mechanism, and possible self-interactions. Strong gravitational lensing provides a purely gravitational means to constrain the particle nature of dark matter through inferences of the properties of dark matter halos. I will discuss how various particle dark matter models affect the abundance and internal structure of dark matter halos, and how we can use strong gravitational lenses observed by HST and JWST to test these predictions on sub-galactic scales.

Tues. May 7: Jamie Bock (JPL / Caltech), virtual Recording

SPHEREx:  An All-sky Infrared Spectral Survey Explorer Satellite
SPHEREx, a mission in NASA’s Medium Explorer (MIDEX) program, is an all-sky survey satellite designed to address three science goals with a single instrument, a wide-field spectral imager.  We will probe the physics of inflation by measuring non-Gaussianity by studying large-scale structure, surveying a large cosmological volume at low redshifts, complementing high-z surveys optimized to constrain dark energy. The origin of water and biogenic molecules will be investigated in all phases of planetary system formation – from molecular clouds to young stellar systems with protoplanetary disks – by measuring ice absorption spectra. We will chart the origin and history of galaxy formation by mapping large-scale spatial power in two deep fields located near the ecliptic poles. Following in the tradition of all-sky missions, SPHEREx will be the first all-sky near-infrared spectral survey, creating spectra (0.75 – 4.2 um at R = 40, and 4.2 – 5 um at R = 135) with high sensitivity using a cooled telescope with a wide field-of-view for large mapping speed.  During its two-year mission, planned to begin in early 2025, SPHEREx will produce four complete all-sky maps that will serve as a rich archive for the astronomy community.  With over a billion detected galaxies, hundreds of millions of high-quality stellar and galactic spectra, and over a million ice absorption spectra, the archive will enable diverse scientific investigations including studies of young stellar systems, brown dwarfs, high-redshift quasars, galaxy clusters, the interstellar medium, asteroids and comets.

Tues. May 14: Nathalie Palanque-Delabrouille (UC Berkley), virtual Recording

Tues. May 21: Cassi Lochhaas (CfA Harvard), virtual Recording

The Non-Equilibrium Circumgalactic Medium
The region of space surrounding galaxies, the circumgalactic medium (CGM), is the site of all gas flows into and out of galaxies and is therefore responsible for regulating or promoting galaxy growth. It has been only in the past couple decades that we have been able to observe this tenuous medium, and even more recently that we have been able to resolve it in cosmological simulations. I will discuss the classical theories for the CGM’s role in galaxy evolution and how new, high-resolution cosmological simulations have shown these theories need serious revision. Using the Figuring Out Gas & Galaxies In Enzo (FOGGIE) simulations that resolve the CGM of Milky Way-like galaxies in exquisite detail, I will describe how dynamic gas motions in the CGM like turbulence, rotation, or bulk radial flows drive the galactic ecosystem out of hydrostatic equilibrium and to lower temperatures than typically assumed, and also disrupt inflowing filaments of gas, ultimately affecting how galaxies accrete new gas to convert into stars. These results suggest that the CGM cannot be well-described using equilibrium assumptions and imply that perhaps the commonly-assumed balance of gas flows in galaxy evolution models need revision as well.

Tues. July 9: Pieter van Dokkum (Yale) (no recording)

Did JWST break the Universe? New insights into the origins of massive galaxies

Fall 2023

Tuesday August 29: Neal Evans (U. Texas at Austin), in person

Why Is Star Formation So Slow?
The problem of slow star formation has been clear for nearly 50 years: simple estimations predict star formation rates more than 100 times what is observed in the Milky Way and other galaxies. Much ingenious theoretical work has been expended to solve this problem, enhancing our understanding of turbulence and feedback in molecular clouds, but the fundamental problem remains. This situation suggests a reconsideration of the basic assumption that underlies the  problem: that molecular clouds are bound entities. In the most complete catalog of structures from CO emission maps, most molecular clouds are unbound, ameliorating the problem. Combining this information with theoretical models of how the star formation rate depends on the initial virial parameter, along with considerations of how metallicity affects the conversion of CO luminosity into mass, leads to correct predictions for the Milky Way, both in total and as a function of Galactocentric radius. Application to other galaxies is also promising but complications exist.

Tuesday September 5: Xuan Du (DRAO), in person Recording

Advance in front-end instrumentation at DRAO: from wideband feed antenna to modeling radio telescopes 
In this talk, I am going to cover the advances we have made at DRAO over the past few years at two forefronts of radio astronomical instrumentation: feed antenna development and better understanding our telescopes (in particular, their polarization properties). In the first part, I am going to introduce the development of a new concept of wideband feed antenna, with the product a 400-1800 MHz feed that is soon going to be commissioned on the DRAO Synthesis Telescope, expanding the current frequency coverage by a factor of 38. In the second part, I am going to present a pipeline that we are building to model radio telescopes in order to understand how well they measure partially polarized radio waves.

Tuesday September 12: Anna Ordog (UBC-O), in person Recording

The polarised radio sky at the DRAO and the quest to understand the magnetized Milky Way
The Milky Way hosts an extensive and complicated Galactic magnetic field structure ranging in scale from stellar environments up to the Galactic spiral arms. Establishing a thorough understanding of the present-day three-dimensional magnetic field morphology is instrumental to developing a complete understanding of the physics of the Milky Way. The magnetized interstellar medium imprints signatures of its structure onto polarisation maps of the radio sky, and a wealth of information can be gained by studying how observed Galactic polarised synchrotron emission varies with frequency through the effect of Faraday rotation. In this talk, I present recent progress toward Galactic polarisation maps from the radio telescopes at the Dominion Radio Astrophysical Observatory (DRAO). Specifically, I show results from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope and the DRAO 15-m single-dish telescope. The data sets will form the low-frequency, Northern hemisphere contribution to the Global Magneto-Ionic Medium Survey (GMIMS), an ongoing international effort to map the entire polarised radio sky covering 300 to 1800 MHz that will yield unprecedented spatial coverage and Faraday rotation resolution for studying large-scale structures in the magnetized interstellar medium (ISM). All previously published and new GMIMS data sets are already yielding fascinating insights into the magnetic field structure, and I highlight some of the early science results. These include: differences between the large-scale patterns in the northern and southern Galactic hemispheres, which inform dynamo models of the magnetic field, examples of Faraday complexity towards objects such as HII regions, and potential methods to distinguish the layers of the magnetized ISM through comparisons of data sets probing different depths.

Tuesday September 19: Yifan Zhou (University of Virginia), remote Recording

Directly imaging protoplanets: the HALPHA survey and beyond.
The direct-imaging detections of accreting young planets herald a new era of planet formation studies, enabling us to witness the process of planet assembly, understand mass accretion mechanisms, and unravel interactions between planets and their birth environment. Ground-based adaptive optics instrument detects planetary accretion by capturing the H⍺ emission from the accretion shock, and the forthcoming ELTs are expected to uncover a large sample of protoplanets. Complementing ground-based telescopes, the Hubble Space Telescope (HST), with its high-Strehl-ratio images and wide spectral range, is invaluable for observing faint host stars and covering ultraviolet wavelengths.
We recently embarked on the Hubble Accreting Luminous Protoplanets in H-Alpha (HALPHA) Survey, which targets accreting planets residing within gaps of transition disks. During my presentation, I will delve into the survey’s motivation, design, and early results. Moreover, I will provide insights into our comprehensive follow-up efforts, employing a combination of time series and multi-wavelength HST data to discern the nature of the protoplanet candidate AB Aur b. Our findings showcase HST’s powerful capability in high-contrast imaging observations and underscore the synergistic potential of space- and ground-based telescopes in directly probing planet formation. Our survey paves the way for characterizations of protoplanets in the ELT era.

Tuesday September 26: Jason Rowe (Bishop’s Unversity), remote Recording

The POET Mission: A Canadian space telescope for exoplanet astrophysics
POET is a proposed Canadian Microsatellite mission designed to characterize and discover transiting exoplanets.  A 20-cm all-reflective telescope will feed a trio of detectors to obtain simultaneous, high duty-cycle, photometry in the u (300-400 nm), Visible Near-Infrared (VNIR) (400-900 nm) and Short Wave Infrared (SWIR (900-1700 nm) bands to make precision measurements of exoplanet transits for atmospheric characterization and to detect transiting Earth-sized planets.  I will discuss the main science drivers of the mission including the impact of recent JWST observations.  POET was selected as a high priority for a Microsatellite mission by the Canadian community as part of the CASCA Long Range Plan 2020.  Advancement of the payload concept and technology development for the optical telescope assembly (OTA) are currently being carried out through the Space Technology Development Program of the Canadian Space Agency. POET is a collaboration between Bishop’s University, Western University, ABB and SFL-UTIAS.

Tuesday October 3: Mike Walmsley (U. Toronto), in person Recording

Title: Reshaping Galaxy Zoo for the Deep Learning Era

Abstract: For the last 15 years, Galaxy Zoo has recruited online volunteers to classify the morphology of millions of galaxies. But Galaxy Zoo is changing. In this talk, I introduce the models we now use to predict how volunteers would describe a galaxy, and consider what these models mean for astronomers.
One clear consequence is scale; our latest catalog, Galaxy Zoo DESI, includes all 8.7M well-resolved galaxies in the DESI Legacy Surveys. But models also allow for entirely new science. They are easily adaptable to new surveys and new tasks, allowing anyone to make exactly their own morphology measurements. The models automatically flag unusual galaxies and make personalised suggestions for which unusual galaxies you might be most interested in. And our latest models (first presented here) can identify which pixels belong to spiral arms or bars. Applying our volunteer-powered models to Euclid and Rubin images, and combining the resulting measurements with ancillary data from DESI spectra and IFU surveys, will reveal how morphology influences galaxy evolution.

Tuesday October 10: Break

Tuesday October 17: Dan Zucker (Macquarie U.), in person Recording

Title: From Little Things Big Things Grow: Tracing the Milky Way’s Assembly History

Abstract: Large galaxies like the Milky Way form hierarchically, with smaller systems merging and accreting to form increasingly massive structures. Evidence for this process can be found all around us: spatially in the form of stellar streams and tidally disrupting satellites in the Galactic halo; dynamically as stellar overdensities in phase space within the Galactic disk; and chemically, in the form of abundance patterns distinct from those of typical stars which formed in situ within the Milky Way. I will briefly outline what we know – or at least, think we know – about the Milky Way’s assembly history, highlighting the work of two ongoing Australian-led spectroscopic surveys, GALAH and S5, in identifying and characterising discrete accretion events. Recent studies with GALAH data clearly show the importance of abundance patterns for detecting accreted structures within the Galaxy, while S5 results I will discuss include evidence for the influence of the LMC on halo stream orbits, an apparent orbital bias in the stellar streams observed, and comparisons with FIRE simulation predictions for detectable streams. I will conclude with a look at the prospects of new facilities such as LSST for driving major advances in our understanding of how galaxies like the Milky Way grow. 

Tuesday October 24:Mathew Lehnert (Centre de Recherche Astrophysique de Lyon), remote Recording

Title: Molecular gas in the proto-cluster and Circum-galactic media in the early universe

Abstract: One of the most outstanding questions in contemporary astrophysics is how did the intercluster/circum-galactic medium acquire its mass and how did it develop the multiphase gas phase distribution we observe today. I present several observational results, but focusing on one in particular, showing that the gas in the intracluster medium of distant proto-clusters and around distant galaxies can be partially molecular.  The distribution of the molecular gas is quite varied. Within this context, I discuss how such gas may have cooled to low temperatures and discuss several theoretical implications of our findings on the nature of gas cycle in distant proto-clusters and massive galaxies.

Tuesday October 31: Sebastiaan Haffert (U. Arizona), remote Recording

Title: High-contrast imaging: the science of detecting faint things next to bright things.

Abstract: High-contrast imaging (HCI) instrument use extreme adaptive optics and coronagraphy to search for faint objects, such as extrasolar planets, around bright stars. To-date, high-contrast imaging has been used almost exclusively to characterize young, self-luminous, massive exoplanets orbiting far from their stars at (near-)infrared wavelengths. However, more mature planets like Earth have cooled off during their evolution and emit little to no thermal emission at optical and near-infrared wavelengths. Starlight that reflects from the top of the atmosphere is the main source of light that will be observable from these planets. Observing reflected light at optical wavelengths will also give us a window into the formation of life in the form of bio-signatures. This signal is very challenging to detect because the Earth-like planets are roughly a billion times fainter than their host star and they also orbit at only a couple times the diffraction-limit. The next generation of extremely large ground-based telescopes (ELTs) and the upcoming habitable worlds observatory (HWO) have the capability to directly image Earth-like planets. However, there is still a major jump in technology that we need to overcome to enable such observations. We need advances in three core technologies: fast and accurate control of the wavefront to counteract dynamic disturbances such as atmospheric turbulence or thermal drifts, optics that block starlight by a factor up to ten billion while letting through planet light at the diffraction-limit and efficient science instruments coupled with advanced data post-processing techniques. I will show how we are using new optics manufacturing technologies to create high-contrast instruments that can reach the fundamental limits of imaging. Such instruments combined with the ELTs will be able to answer a question that has captivated mankind for millennia: are we alone?

Tuesday November 7:Jacqueline Antwi-Danso (U. Toronto), remote Recording

Title: Too Big to Be?: Searching for the Most Massive Galaxies in the Distant Universe

Abstract: One of the unsolved problems in extragalactic astronomy is understanding the physics of how galaxies grow their stellar mass over cosmic time. Large-scale hydrodynamical simulations have been largely successful in matching the basic properties and number densities of galaxies at z < 2.5 (covering the past 11 Gyr). This has given us confidence in our understanding of the physics thatregulates star formation and quenching over most of cosmic history. However, at earlier cosmic times, simulations underestimate the number densities of massive galaxies by a shocking 1-2 orders of magnitude. While this issue has largely been overlooked for the past decade, recent JWST discoveries of massive galaxies observed at even earlier times than we thought possible have brought this tension with theory back to the limelight. In this talk, I will give an overview of the systematics contributing to this discrepancy between theory and observations, as well as our best attempts at addressing it using (1) medium-band galaxy surveys; (2) novel color-color selection methods; and (3) physically motivated star-formation histories. I will also discuss my upcoming JWST Cycle 2 program and a few others geared at obtaining precise redshifts, stellar masses, and chemical abundances of massive galaxies at z > 3. 

Tuesday November 14: Christina Williams (U. Arizona), remote Recording

Title: The dark side of massive galaxies and new light with JWST

Abstract: Our most powerful telescopes have glimpsed galaxies in their early growth phase only a few billion years after the Big Bang. In past decades, galaxy surveys showed that the most massive galaxies in the Universe must have formed the earliest in cosmic time, in extreme but short-lived bursts of star-formation. However, owing to their optical faintness and extremely red spectral energy distributions, early massive galaxies have historically been challenging to study. JWST is now revealing the early phases of massive galaxy growth at high redshift, and in this talk I will discuss the numerous surprises and new questions raised since JWST launch. Ultimately a more comprehensive census of the early Universe will come from larger area surveys, and I will conclude with preliminary findings about the large-scale abundance of bright massive galaxies from the JWST wide-area PANORAMIC survey.

Tuesday November 21: Matt McQuinn (U. Wash.), in person Recording

Title: A new concept to measure geometrically the expansion of the universe

Abstract: With several >~4 meter radio dishes in the outer solar system, it appears possible to measure the distances to fast radio bursts that originate hundreds of megaparsecs away and thereby measure the cosmic expansion history using a geometric method that is similar to the trilaterations of global satellite navigation systems (https://arxiv.org/abs/2210.07159
).  The sensitivity scales quadratically with dish separations such that distance measurements to bursts even on the other side of the observable universe may be possible.   Not only could this technique potentially provide a much more precise geometric constraint on the cosmic expansion history, but such
a mission could also provide interesting constraints on micro-Hertz gravitational waves, pulsars, the outer solar system, and the dark matter.   While this idea is ambitious, and there is certainly an argument that we do not need to measure the expansion better than we already have (which I will address), another reason to attend this talk is that this concept involves so much interesting physics related to GPS systems, very long baseline interferometry, plasma propagation effects, gravitational time delays, and
the diffuse outer solar system.

Tuesday November 28: Caitlin Casey (U. Texas at Austin), remote Recording

Title: Formed too Fast: Massive Galaxies at Cosmic Dawn

Abstract: The pace of galaxy growth in the early Universe offers one of the most accessible tests of the Lambda-CDM cosmological framework. A growing number of surprisingly massive galaxies are now being found in the first billion years after the Big Bang that push the limits of theoretical predictions. Unusually bright high-redshift galaxies discovered by JWST challenge our most fundamental models of how fast stars form.  Some of them contain overly massive black holes whose formation is uncharted. Massive dusty starbursts found with ALMA are requiring new explanations about early dust production.  The spatial distribution of massive galaxies within large scale structure may be more highly clustered than expected, which would impact the timescale and uniformity of reionization — the last major phase change of the Universe from a neutral to ionized medium.  I will present an overview of large, multi-wavelength observational campaigns I lead to place the first comprehensive constraints on the rarest, most massive galaxies to emerge at z>6 and the impact they in turn have on our interpretations of the early Universe. These efforts unite the unprecedented sensitivity of JWST together with ALMA and Keck to work towards the goal of definitively establishing the story of how and when the first galaxies assembled.

Tuesday December 5: Cancelled

Tuesday December 12: Stella Offner (U. Texas at Austin), remote Recording

Title: Our Lonely Sun: How Multiple Star Systems Form (or don’t)

Abstract: Most stars are born with one or more stellar companions. Observational advances over the last decade have enabled high-resolution, interferometric studies of forming multiple systems and statistical surveys of multiplicity in star-forming regions. These have yielded new insights into how such systems form and how multiplicity affects disk evolution and planetary architectures. In this talk, I will review recent observational discoveries of the youngest multiple systems. I will present the results of star cluster simulations modeling the formation and evolution of multiple systems, and I will discuss the role of dynamics and environment in setting stellar multiplicity.  Finally, I will highlight remaining numerical and observational challenges.

Tuesday December 19: Kristen Dage (McGill), remote Recording

Title: Ultraluminous X-ray Sources in Extragalactic Globular Clusters

Abstract: Currently, ultraluminous X-ray sources (ULXs) with globular cluster (GC) counterparts have been identified. This is exciting, as ULXs have been theorized as potential intermediate mass black holes. New black hole mergers detected by LIGO-Virgo may also be associated with GC’s, underscoring the importance of ULXs as a potential linkage between GC electromagnetic and gravitational wave source populations. GC ULXs show a diverse behaviour with regards to temporal variability, both on long (16 years) and short (~hours) timescales, in both the X-ray and optical wavelengths. They can switch on or off over the course of many years or remain at a constant luminosity. Some sources exhibit a long-term change in their luminosity with no discernible variability within the other observations, other sources show a stunning long-term variability while also demonstrating variability on the timescale of around four hours. I will undertake a comprehensive comparison of the temporal variability of the zoo of currently known GC ULXs, discuss the possible origins of some of the extreme variability observed, and how this informs on our knowledge of black hole populations in extragalactic globular clusters.

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Winter/Spring 2023

Tues January 17, 11am, Norm Murray (CITA), in person Recording

Why the day is 24 hours long
The length of the day and the month are seen to be increasing, due to gravitational tidal torques. Geologic data suggests, however, that between about 2,000 million years ago (Ma) and 1,000 Ma, the length of day (LOD) was fixed at about 19.5 hours, while the length of the month was increasing. Following a suggestion by Zahnle and Walker in the 1980’s, I and my co-workers explore the hypothesis that the fixed LOD results from the Solar thermal atmospheric tide, which was stronger in the past, due in part to a resonance in Earth’s atmosphere. Absent this resonance, the LOD today would be around 60 hours. We use two global circulation models (or GCMs), PlaSim and LMD, to estimate the frequencies of normal modes (or free oscilliations) in Earth’s atmosphere, finding excellent agreement with recent measurements. Using the GCMs, we show that an atmospheric resonant period of 19.5 hours corresponds to a mean global surface temperature T in the range 40-50 C; the GCMs show that T could have been that high despite the lower Solar flux 2,000 Ma, if the partial pressure of CO2 was of order a tenth of a bar, compared to the present day value of 0.0004 bar. This is at the upper range of estimates 1,500 Ma based on geochemical and paleosoil evidence. Thermal tides are likely to have affected the length of day of many exoplanets.

Tues January 24, 11am, Kevin Casteels (HAA), in person Recording

Complex Spacetime and Luminosity Driven Expansion
The two pillars of modern physics, Quantum Mechanics and General Relativity, interpret reality in very different ways, the former as purely statistical, and latter purely geometrical. This apparent incompatibility can be reconciled through the use of complex math to describe spacetime. We will explore previous work done on Complex Spacetime including recent studies which show imaginary numbers aren’t merely a mathematical convenience, but essential to describe observation. A new model will be described which treats real spacetime as composed of two imaginary parts, or layers, which mix to create real space. One of the predictions of this model is that when mass is converted to energy, the real space metric expands by an amount proportional to the photon’s half wavelength. We will explore the consequences of this prediction, and calculate expansion rates for various objects. It is found that the Local Group of Galaxies produces a luminosity driven expansion rate of ~70 km/s, which is comparable to measurements of the Hubble flow. When considering galaxy clusters, the luminosity driven real space expansion would act to increase the observed velocity dispersions, giving virial mass estimates several times greater than the observed baryonic mass, potentially removing the need for large dark matter components in these systems.

Tues January 31, 11am, Melissa Graham (UWash), in person Recording

Supernova Science with Large Sky Surveys
As the endpoints of stellar evolution, sources of dust, and cosmological standard candles, supernovae are a useful and important astrophysical phenomenon to understand. In this talk I will describe how I use large sky surveys and targeted follow-up to constrain the physical nature of Type Ia supernovae (SN Ia), the thermonuclear explosions of carbon-oxygen white dwarf stars. I will also provide a look towards the future with the Rubin Observatory, which will detect millions of supernovae over its 10-year Legacy Survey of Space and Time (LSST). I am currently a research staff scientist at the University of Washington in Seattle, and I hold the roles of Data Management Science Analyst and Lead Community Scientist for the Rubin Observatory. This talk will also cover how individuals without Rubin data rights can participate in LSST science, and provide an inside look at how Rubin staff are preparing themselves — and the science community — for the data revolution of the LSST.

Tues February 7, 11am, Joan Najita (NOIRLab), on zoom Recording

Clues to Our History from Debris Disks and the Dynamics of Andromeda’s Halo

Abstract: The patterns we notice in astronomical data can provide simple but valuable clues to how systems evolve and to our own origins. I’ll share two examples. (1) The similar sizes of the spectacular rings observed in protoplanetary disks and debris disks suggest that they share a common origin. New calculations of the evolution of rings of pebbles and planetesimals lead us to a simple picture in which large protoplanetary disks evolve into the known bright debris disks, with our Solar System following a distinct evolutionary path that originates in compact disks. (2) Data recently obtained by DESI, the highly multiplexed multi-object spectrograph on the 4m Mayall Telescope on Kitt Peak, reveal delicate structures—streams, wedges, and chevrons—in the positions and velocities of individual stars: evidence of a recent galactic immigration event in exquisite detail. The observations may open a window onto our past, offering a view of what our own galaxy may have looked like billions of years ago. 

Tues February 14, 11am, Jessie Christiansen  (Caltech), in person Recording

Towards an Exoplanets Demographics Ladder
The NASA Kepler mission has provided its final planet candidate catalogue, the K2 mission has contributed another four years’ worth of data, and the NASA TESS mission has been churning out new planet discoveries at a rapid pace. The demographics of the exoplanet systems probed by these transiting exoplanet missions are complemented by the demographics probed by other techniques, including radial velocity, microlensing, and direct imaging. I will walk through the progress of the Kepler occurrence rate calculations, including some of the outstanding issues that are being tackled. I will present our new results from K2 and TESS, and outline how K2 and TESS will able to push the stellar parameter space in which we can explore occurrence rates beyond that examined by Kepler. Finally, I will highlight some of the pieces of the larger demographics puzzle – occurrence rate results from the other techniques that probe different stellar and exoplanet regimes – and progress to be made working to join those pieces together.

Thursday March 9, 11am, Mark Voit (MSU), in person Recording

Tues March 14, 11am, Alex Cameron (Oxford), in person Recording

Chemical evolution of galaxies from the early Universe to the present day
Rest-frame optical emission lines offer one of our most powerful and well-studied probes of chemical abundances in the ISM of galaxies. With the advent of JWST/NIRSpec, we can now study rest-optical emission spectra at z>9, within the first 0.5 Gyr after the Big Bang, allowing us to measure metallicities in the interstellar medium (ISM) of galaxies over almost the entirety of cosmic history.
Meanwhile, integral-field unit (IFU) spectrographs on current and future ground-based telescopes are enabling new constraints to be placed on chemical abundances in different phases of galaxies, such as from emission lines in extended diffuse emission. The combination of these cutting-edge facilities presents an opportunity to track chemical enrichment throughout the Baryon cycle in unprecedented detail.
In this talk I will present early results from the JWST Advanced Deep Extragalactic Survey (JADES), a combined NIRSpec + NIRCam large GTO program studying galaxy evolution from z~2 out to the highest redshifts observable with JWST. In particular, I will focus on what these (and other) early JWST observations are already telling us about the ISM conditions in high redshift galaxies, including some very intriguing findings from a recently published spectrum of GN-z11 (an ultra-luminous galaxy at z=10.60).
I will also present results from the DUVET survey, an IFU survey targeting low-redshift starburst galaxies, in which we have present direct measurements of outflow metallicity, affording new constraints on how these galaxy-scale gas flows are shaping the chemical evolution of galaxies.
However, deriving chemical abundances is notoriously susceptible to systematic uncertainties.
I will discuss our recent efforts to model the emission lines measurements from outflows, which are helping to unpick the systematic uncertainties involved in making these novel outflow metallicity measurements.

Tues March 28, 11am, Tarraneh Eftekhari (Northwestern), in person

Uncovering the Elusive Origin of Fast Radio Bursts
Upgrades in multiple fast radio burst (FRB) experiments have led to a growing sample of precisely localized events, enabling host galaxy associations and detailed observations of the immediate environments surrounding FRBs. Such observations play a key role in elucidating the stellar populations that give rise to FRB progenitors. Indeed, host galaxy demographics, as well as the spatial offsets of FRBs from their host galaxy centers, can be used to inform progenitor channels. The localizations of two repeating FRBs to dwarf galaxies, their coincidence with persistent radio sources, and their large observed excess dispersion measures (DMs) stand in stark contrast to other localized events, which generally reside in more massive galaxies and exhibit modest excess DMs. Understanding this dichotomy among FRB hosts will provide critical insight into the stellar populations prevalent in FRB host galaxies and hence their likely progenitors. In this talk, I will review our current knowledge of FRB progenitors based on the properties of a small, but growing sample of host galaxies. I will also outline key follow-up observations that will lend to detailed characterizations of the galactic and local environments of FRBs, thereby shedding light on their progenitor channels. 

Tues April 4, 11am, Kartheik Iyer (Columbia), on zoom Recording

From cosmic dawn to cosmic noon: studying galaxy evolution using star formation histories in the era of JWST
A diverse range of physical processes are responsible for regulating star formation across galaxies. Understanding their relative contributions to galaxy growth and quenching at different epochs is one of the key questions in galaxy evolution today. Since these processes are thought to have characteristic timescales, studying their imprints on galaxy star formation histories (SFHs) helps quantify their contributions for a population of galaxies. In this talk, I will describe a framework for modeling galaxies as Gaussian processes, that can be applied to both theory and observations to (i) establish a formalism to study the variability of star formation across different timescales and analyze cosmological galaxy evolution simulations, and (ii) reconstruct the star formation histories of galaxies observed using HST and JWST (from the CANUCS and CEERS surveys). Taken together, simulations and observations leverage predictive power against observational constraints, and allow us to develop a fuller picture of how galaxies evolve over time.


Tues April 11, 11am, Melissa Amenouche (HAA), in person Recording

Tues April 18, 11am, Leonardo Ferreira (UVic), in person Recording

The Optical Morphologies of Galaxies beyond z~3 with JWST
The launch of JWST with its powerful infrared capabilities has opened up a new window for studying the resolved optical morphologies of galaxies beyond z~3. Prior to this, morphology studies in the early Universe were limited to the ultraviolet portion of the electromagnetic spectrum. This narrowed our ability to track the bulk of stellar masses in high redshift galaxies, as the UV mainly captures clumpy star formation and other energetic phenomena. We present our findings from a visual classification effort of 4265 galaxies observed with JWST at $1.5 < z < 8$ in the JWST CEERS observations that overlap with the CANDELS EGS field. By employing a simple classification scheme to produce disk/spheroid/peculiar classifications, we find a strong dominance of morphologically selected disk galaxies up to z~8, a far higher redshift than previously thought possible. Our results suggest that most stars in the Universe were likely formed in a disk galaxy, and that these morphological populations are consistent with predictions from cosmological simulations.

Tues April 25, 11am, Hao He (McMaster), on zoom Recording

Evolution of Giant Molecular Clouds in Nearby Starburst Mergers
Starburst mergers represent a common population of galaxies in early universe and hence are great laboratories to study the star formation (SF) in these most extreme environments. Due to the rarity of mergers in the local universe, we do not have large observed samples that are close enough to study individual giant molecular cloud (GMC) properties. In this work, we employ idealized galaxy merger simulation based on the Feedback In Realistic Environments (FIRE-2) physics model to study how the properties of GMCs evolve at different merging stages. We conduct a pixel-by-pixel analysis of molecular gas properties in both the simulated control galaxies and galaxy major mergers. The simulated GMCs in the control galaxies follow a similar trend in a diagram of velocity dispersion (σv) versus gas surface density (Σmol) to the one observed in local spiral galaxies in the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey. For GMCs in simulated mergers, we see a significant increase of factor of 5 – 10 in both Σmol and σv during the second passage along with the fact that more than 50% of molecular gas is concentrated in the central 1 kpc region. GMCs during the second passage also exhibit much higher virial parameters (αvir) reaching 10 – 100, which suggests they are much less gravitationally bound compared to GMCs in normal spiral galaxies. Furthermore, we find that the increase in αvir happens at the same time as the increase in global star formation rate (SFR), which suggests stellar feedback is responsible for dispersing the gas. We also find that the gas depletion time (tdep) is significantly lower for high αvir GMCs during a starburst event. This is in contrast to the simple physical picture that low αvir GMCs are easier to collapse and form stars on shorter depletion times. This might suggest that some other physical mechanisms besides self-gravity are helping the GMCs in starbursting mergers collapse and form stars. Instead, we find significant anti-correlation between average Σmol for GMCs and tdep, which might be due to higher fraction of dense gas that leads to shorter tdep. In the future, we will gather a larger sample of observed starburst mergers (~40) with GMC-resolution CO 2-1 ALMA archival data to perform a comprehensive comparison between observation and simulation.

Friday April 28, 11am, Katherine de Kleer (CalTech), in person Recording

Tues May 9, 11am, Pallavi Patil (NRAO), in person Recording

Tues May 16, 11am, Alberto Saldana-Lopez (University of Geneva), in person Recording

A low-redshift look to reionization with star-forming galaxies
One of the current hot topics in galaxy evolution is the so-called Cosmic Reionization, the last major cosmic phase by which the Universe transitioned from a neutral to a (mostly) ionized state, happening around z = 6-9. The main responsible sources for reionization are still under debate, but star-forming galaxies seem to be the likeliest due to their high number density at early epochs respect to Active Galactic Nuclei.
However, directly probing ionizing (also called Lyman Continuum, LyC) radiation from galaxies at the Epoch of Reionization is difficult, since the escaping photons are likely absorbed by the remaining neutral gas in the intergalactic medium (IGM). Therefore, in order to study the role of star-forming galaxies during Reionization, we need to rely on indirect indicators of such emergent LyC radiation. The low-redshift Universe offers a unique window to study the properties of LyC-emitting galaxies, since the IGM attenuation is negligible and, at the same time, a full suite of multi-wavelength observations is available both from space and the ground.
Recent HST campaigns such as the Low-Redshift Lyman Continuum Survey (LzLCS) has nearly tripled the number of LyC detections at low-redshift. The LzLCS has revealed that compact star formation, high ionization parameters, strong and narrow LyA emission, low dust-attenuation and the presence weak absorption lines seem to characterize the spectra of the strongest LyC emitters. In this talk, I will present some of the main results of the LzLCS and explain how this data set has changed our understanding of the mechanisms for LyC escape. We will also discuss the implications of these results for the high redshift community in the JWST era.

Tues June 6, 11am, Vincent Henault-Brunet (St Mary’s), remote Recording

Fall 2022

Tues Aug 23rd, 11am, In person: Adam Stevens (University of Western Australia) Recording

Models, simulations, and surveys: towards a convergent theory of galaxy evolution across environments:
After decades of hype and advancement, galaxy evolution remains one of the forefront research fields of astrophysics. The ultimate challenge lies in developing a theoretical framework that not only covers the vast breadth of astrophysical processes that affect galaxies’ formation and evolution, but also predicts and explains the enormous and ever-growing wealth of multi-wavelength observational data we possess. In this talk, I will provide an overview of modern galaxy formation models, cosmological simulations, and low-redshift galaxy surveys. I will discuss how we test the outcome of our models against our observational data, with a focus on galaxy surveys that measure gas content in the local Universe. In particular, I will highlight research into the influence of galaxy environment on the acquisition and expulsion of galaxies’ gas. With simulation suites like IllustrisTNG, and radio surveys like VERTICO and WALLABY, we are riding a new frontier of insight into the gas flows of galaxies in dense environments.

Tues Sept 20th, 11am, Zoom: Viraja Khatu (University of Western Ontario)

UV Time Lag for Hbeta Emission in a Highly Accreting AGN, Markarian 142
Growing at the centres of massive galaxies, active galactic nuclei (AGN) are supermassive black holes surrounded by an accretion disk of ionized gas and dust.  In AGN, matter accreting onto the central black hole releases tremendous amounts of energy.  During the peak era of black hole growth (redshifts, z = 1 to 3), AGN witnessed episodes of high accretion rates well above their super-Eddington limits.  Several theoretical studies predict a ‘slim’-disk structure for highly accreting AGN; however, their observational studies are rare.  We focussed on studying the structure of Markarian 142 (Mrk 142) – a low-redshift (z = 0.045) AGN accessible at multiple wavelengths – using data from both ground and space observatories.  We determined an ultraviolet (UV) time lag for the Hbeta emission in Mrk 142, for the first time, with simultaneous photometry (from Swift and Las Cumbres Observatory) and spectroscopy (from the Gemini North and Lijiang Telescopes).

Tues Sept 27th, 11am, In person: Chelsea Spengler (Pontificia Universidad Católica de Chile) Recording

The origins and growth of nuclear star clusters
It is readily accepted that many galaxies are inhabited by dense, compact objects deep in their centres, manifesting as supermassive black holes and/or nuclear star clusters (NSCs). Their widespread presence and apparent similar scaling relations with properties of their hosts implies that these black holes and NSCs are two related flavours of central massive object that play essential roles in their hosts’ evolution. How do these NSCs form? How do they relate to black holes, their host galaxies and their broader environment? Addressing these questions requires sensitive observations of lower-mass galaxies where NSCs dominate. In this talk, I will describe the results of a detailed study of the stellar populations of NSCs using surveys of the Virgo Cluster completed with the Hubble Space Telescope. Then I will shift to work with the Next Generation Virgo Cluster Survey (NGVS), which provides unprecedented depth and coverage of over 3,600 galaxies in the Virgo Cluster and expands our sample of cluster members to new low-mass regimes — enabling a thorough exploration of the photometric properties of NSCs ranging from the dense Virgo core to more diffuse groups still falling into the cluster potential. Lastly, I will introduce a density-based hierarchical clustering algorithm used to identify various substructures and environments throughout Virgo using the NGVS.

Tues Oct 4th, 11am, Zoom: Phoebe Upton Sanderbeck (Los Alamos National Laboratory) Recording

Signatures of primordial origins around supermassive black holes 
Primordial black holes (PBHs) can plausibly be as large as 100,000 solar masses, if formed at approximately one second after the Big Bang. Such massive PBHs could be the seeds of the supermassive black holes powering early quasars both because of their large mass and early formation time. These PBHs form prior to Big Bang nucleosynthesis, and so affect primordial nucleosynthetic abundances due to a local change in the expansion rate near the black hole. I will present predictions for these modulated abundances, specifically in helium, deuterium, and lithium. Narrow band observations of the He1640 emission line with the James Webb Space Telescope would serve as an ideal probe of such modified helium abundances.

Tues Oct 11th, 11am, In person: Adam Smercina (University of Washington) Recording 

The Assembly of Nearby Galaxies’ Satellite Populations through Group Accretion
The hierarchical formation of galaxies like the Milky Way (MW) is a central prediction of the Lambda-Cold Dark Matter (LCDM) model. Galaxies like our MW are predicted and observed to host vast halos of stars accreted from disrupted dwarf galaxies, as well as rich dwarf satellite populations — both of which tantalizingly encode details of their formation histories. This regime has long been problematic for galaxy formation simulations, due to the required resolution, and observational progress has been largely constrained to the Local Group, due to the intrinsic faintness and large physical scales of both features. To address this observational deficit and generate more useful comparison samples for simulations, I have contributed to a field-wide effort to survey the halos and satellites of nearby MW-mass systems. With observations from wide-field, ground-based surveys, we are able to measure nearby galaxies’ stellar halos to unprecedented depths and detect their complete satellite populations. Combined with insight from similar studies in the community, we have learned that both the stellar halos and satellite galaxy populations of MW-analogs are remarkably diverse – and, surprisingly, appear to be related. The number of dwarf satellites around MW-like galaxy hosts is tightly correlated with the mass of its largest merger. I will show that this relationship could help to explain findings of coordinated star formation cessation in the MW and M31 groups, and recent signatures of group infall of faint satellites in the M81 system. The tightness of this correlation cannot currently be explained in high-resolution zoom or cosmological simulations, such as FIRE and TNG50. The tension between the observed and predicted connection between two fundamental outcomes of hierarchical assembly represents an important gap in our understanding of galaxy formation. Expanding these studies to lower-mass and more distant systems, and pushing to fainter dwarf detection limits, will guide this science into the next generation of observational facilities and cosmological simulations.

Tues Oct 25th, 11am, In person: Ilsa Cooke (UBC) Recording 

Unraveling the organic chemistry of dense clouds: interstellar molecules and the laboratory tools we use to study them
Molecules are not limited to our solar system but exist in the extreme environments found in interstellar space. Astrochemistry is the study of this rich and diverse chemistry that occurs throughout the universe. Our picture of the molecular universe is becoming increasingly complex with around 250 molecules identified in the interstellar medium, and the rate of new detections still growing.
Dense molecular clouds are the earliest stage of star formation and provide the molecular material that will make up new planets and solar systems. I will present our recent observations of a particular molecular cloud in Taurus, TMC-1, including the detection of the first interstellar polycyclic aromatic hydrocarbons. In order to understand how these molecules can form in TMC-1, laboratory experiments must be conducted down to temperatures below 10 K to measure the kinetics of key reactions. The study of reactions at these low temperatures, including measurements of the reaction rate coefficients and product-branching-ratios, presents substantial experimental challenges. I will discuss the implementation of the CRESU technique (a French acronym for Reaction Kinetics in Uniform Supersonic Flow) as a method to measure low temperature reaction kinetics relevant to interstellar space.

Tues Nov 8th, 11am, Zoom: Ziggy Pleunis (Dunlap Institute) Recording

Uncovering the diversity of fast radio bursts
Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of elusive origin that were first discovered in 2007. They are unique probes of the density and magnetization of the interstellar and intergalactic media and they will be even more useful when we better understand their sources, emission and environments. A small fraction of FRBs has been observed to repeat, which has ruled out a cataclysmic origin for these sources and allows for detailed multi-wavelength follow-up observations that constrain FRB models. It is as-of-yet unclear whether all FRBs repeat and if FRB models based on a few well-studied repeaters can be extrapolated to the full population. Canada’s CHIME telescope has been instrumental in uncovering the diversity of FRBs: it provided the first statistical sample of FRBs and it discovered the vast majority of the repeating sources by revisiting the Northern sky every day for the last four years. I will present the differences between repeaters and apparent nonrepeaters that have emerged, with a focus on observations from CHIME/FRB, and I will discuss how the differences can/cannot be reconciled with one population of FRBs.  

Tues Nov 15th, 11am, Zoom: Jiayi Sun (McMaster University) Recording

A Multiwavelength and Multiscale View of Star Formation across the Local Universe
I will summarize recent advances in understanding star formation across large samples of local galaxies. These advances are enabled by state-of-the-art observations with ALMA, VLT/MUSE, and HST, which discern fundamental units of star formation (molecular clouds, HII regions, and star clusters). Observational evidence suggests that molecular clouds, which set the initial/boundary condition of star formation, are strongly coupled to the large-scale properties of their host galaxy. Once star formation takes place, feedback from young stars quickly disperse the natal cloud, resulting in an overall low star formation efficiency. While this process is violent and highly non-equilibrium on 10-100 pc scales, star formation in massive disk galaxies appears self-regulated when averaging over kpc-scale regions: through momentum and energy injection, stellar feedback counteract turbulence cascade and cooling processes and keeps the interstellar medium (ISM) in a quasi-equilibrium state. I will also showcase some early science results based on recent JWST observations, which offer an unprecedented view of intricate ISM structures and heavily embedded star formation.

Tues Nov 22nd, 11am, Zoom: Josh Speagle (University of Toronto) Recording

Galaxy Evolution through the Eyes of the Milky Way
Galaxies are complex systems whose evolutionary pathways lead to a huge variety of present-day outcomes. Disentangling the physics involved requires a delicate balancing act between exploring details of physical processes taking place in our Galaxy/nearby galaxies and studying the overall evolution of many galaxies across cosmic time. I will discuss the ongoing journey my collaborators and I are taking to try and pin down various parts of this story and how the Milky Way fits in. It will include attempts to resolve a long-standing conundrum about how star-forming galaxies assemble most of their stellar mass over time, a variety of applications of statistical modelling and machine learning, comparisons with cosmological simulations, and the search for Milky Way “analogues”. It will also include a few unexpected surprises (well, at least they were to me!). If time permits, I will close with some discussion on promising avenues for future work.

Tues Nov 29th, 11am, In person: Maaike Van Kooten (HAA)

Towards extreme adaptive optics for giant segmented telescopes: the impact of atmospheric turbulence from multi-decadal to millisecond timescales

While adaptive optics (AO) systems have now been deployed on nearly every 10-meter-class observatory, the state-of-the-art in AO technology development does not yet meet the needs of the next generation of giant, segmented telescopes, especially in the context of direct imaging and characterization of exoplanets. In this talk, I address the impact of atmospheric turbulence on AO systems, focusing on two very different timescales, investigating: 1. over the last 40 years, what are the effects of climate change on optical turbulence and, therefore, the performance of our AO systems, and 2. can we predict turbulence on milli-second timescales to improve the performance of our AO system? The talk will be divided into two parts, where I first introduce the climatology of Maunakea using summit data and numerical weather model output (i.e., re-analysis datasets such as ERA5).  The second half of the talk will focus on technology development specifically for high contrast imaging (HCI). As the HCI community prepares for giant segmented telescopes and pushes toward contrasts enabling the direct imaging and characterization of radial-velocity detected exoplanets, the performance of the AO system needs to be improved. I will present on-sky results from testing advanced AO methods on W.M. Keck Observatory, showing that by predicting the evolution of the turbulence on timescales of the AO system we can improve achievable contrast for the NIRC2 instrument.

Tues Dec 6th, 11am, Zoom: Alex Tetarenko (Texas AM) Recording

Towards micro-arsecond imaging in stellar-mass black holes

Very Long Baseline Interferometry (VLBI) is a powerful diagnostic tool that can be used to study black holes. Today’s state of the art global mm-VLBI arrays are able to achieve tens of micro-arcsecond resolution, enabling imaging down to event horizon scales in some super-massive black hole sources. While stellar-mass black holes within our own Galaxy are located much closer than these extra-galactic sources, their black holes are millions to billions of times smaller in mass, thus direct imaging on horizon scales is not feasible. However, global mm-VLBI arrays could allow us to directly resolve their extended jets and open the door to extracting new physics (e.g., size scale of the emitting region, velocity of the jet flow, the alignment of the jet axis, morphology, energetics, and the particle energy distribution). In this talk, I will discuss how we are beginning to build the foundation needed to overcome both the observational and analysis challenges that accompany mm-VLBI studies of stellar-mass black hole systems. In particular, I will highlight what we can do with the current VLBI architecture, as well as detail the crucial role that next generation instruments and algorithmic development play in these efforts.

Tues Dec 13th, 11am, Zoom: Mike Chen (Queens University)

Assembling Star-forming Structures in Molecular Clouds

Star formation is a highly multi-scaled process that takes place in turbulent molecular clouds. How these clouds assemble their diffused gas into dense structures that can collapse directly to form stars is still poorly understood. While we have made significant progress in structural studies over the last decade and learned that filaments play a crucial role in such an assembly, we only recently began to probe the behavior of gas kinematics and magnetic fields within these filaments. In this talk, I will present one of the first systematic kinematic studies of star-forming filaments and how it informs us about the filamentary assembly of star-forming gas. Moreover, I will go over how these results connect with higher-resolution case studies and the latest magnetic field studies to construct a more holistic understanding of the star-forming process in the nearby clouds.

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Winter/Spring 2022

Tues February 8th, 11am,  Zoom: Simon Blouin (U. of Victoria) Recording

White dwarf crystallization as revealed by Gaia: White dwarf evolution is often described as a simple cooling process that naturally provides accurate age determinations. In reality, fundamental aspects of white dwarf cooling remain poorly understood. The extent of current uncertainties has been clearly demonstrated by Gaia DR2, which revealed that some white dwarfs undergo multi-Gyr cooling delays not predicted by current cooling models. In this talk, I will present my recent theoretical work aimed at improving the constitutive physics of white dwarf cooling models (in particular the physics of core crystallization) and discuss outstanding uncertainties that should be addressed before white dwarf cosmochronology can reach its full potential.

Tues February 15th, 11am,  Zoom: Katja Fahrion (ESA) Recording

Deciphering the formation of nuclear star clusters: Nuclear star clusters (NSCs) are dense, massive star clusters found in the centres of at least 70% of all galaxies. NSCs are known to co-exist with central black holes (BHs), our own Milky Way being the most prominent example, and are known to follow the same scaling relations with host galaxy properties, suggesting a connected evolution. To understand the detailed buildup of galactic nuclei we can study NSCs that still contain records of their formation and evolution imprinted in their stellar populations and kinematics. Generally two main scenarios are discussed for NSC formation: in-situ from gas at the galactic centre or via the dissipationless accretion of globular clusters (GCs) that spiral inwards due to dynamical friction. Most likely, a mixture of both pathways is realized in nature, but the dominant channel nor the mass fractions are unknown. I will present recent results from integral-field spectroscopy of NSCs hosted by dwarfs and massive early-type galaxies that allow to constrain NSC formation for individual galaxies. These results indicate a clear dependence of the dominant NSC formation channel from GC-accretion to in-situ formation with increasing galaxy and NSC mass.

Tues February 22th, 11am,  Zoom: Freeke van de Voort (Cardiff U.) Recording

Cosmic gas flows in the circumgalactic medium: Galaxies are intimately connected to the environments they live in. The haloes around them contain the gas reservoir from which the galaxies grow, while galactic outflows heat and enrich this ‘circumgalactic medium’ (CGM). Using ‘zoom-in’ cosmological, magnetohydrodynamical simulations, I will discuss some of the physical and observable properties of the gas around galaxies, focusing on Milky Way-like systems. The simulations use a new refinement technique to reach orders of magnitude higher resolution in the CGM than the current state-of-the-art. These spatially refined simulations show that the CGM has more ‘cool’ gas than previously thought, which strongly affects predicted observables in the CGM: The neutral hydrogen column densities are greatly enhanced, more in line with observations. Furthermore, I will show how the presence of magnetic fields alters the gas flows into and out of galaxies, which results in less (metal) mixing and higher gas fractions inside the halo and changes the properties of the CGM. I will also briefly discuss the effects of the enhanced resolution and presence of magnetic fields on the galaxies themselves.

Tues March 8th, 11am,  Zoom: Bala Chaudhary (Dartmouth) Recording

Strategies for antiracist action in STEM

Tues March 15th, 11am,  Zoom: Steven Goldman (STScI) Recording

Probing the Evolution of Stars, Dust, and Galaxies using Evolved Stars: Asymptotic Giant Branch stars play a number of roles in the evolution of dust, galaxies, and the ISM. This complex and short-lived phase of evolution is the key to calibrating stellar and chemical evolutionary models, dust budget calculations, and understanding the regeneration of the Universe. AGB feedback is an important parameter in cosmological simulations and has also been invoked to explain the multiple stellar populations in globular clusters. Despite their importance, their mass-loss and dust production mechanisms remain unclear. I will discuss the results of recent large observing programs with the Hubble and Spitzer Space Telescopes (PHAT, SAGE, DUSTiNGS). These programs have allowed us to study the impact of AGB stars on their environment and vice-versa; how the late stages of all low-to-intermediate mass stars might impact massive galaxies, dwarf galaxies, and high-redshift galaxies. I will summarize the results of these observing programs, discuss the recent advancements in AGB modeling, and advocate for the future prospects of AGB studies in nearby galaxies.

Tues March 22nd, 11am,  Zoom: Victoria Strait (DAWN) Recording

What have we learned about early galaxies before JWST?: Constraints on physical properties of early galaxies in the redshift range z ~ 6-10 (just a few million years after the Big Bang) are key for a full understanding of the process of reionisation and early galaxy evolution, including the onset of star formation. I will present results on the highlights from my study of ~200 z ~ 6-10 galaxy candidates from the Reionisation Lensing Cluster Survey (RELICS) survey which utilises galaxy clusters as comic lenses to magnify faint sources. This will include a variety of results about specific exciting galaxies using data from the Hubble Space Telescope, Spitzer Space Telescope, and the Keck Telescopes. Additionally, I will discuss some exciting prospects for the recently launched James Webb Space Telescope. 

Tues March 29th, 11am,  Zoom: Alessandro Lupi (U. of Milan-Bicocca) Recording

Massive black holes in high-redshift quasar hosts: formation and evolution: The observations of high redshift quasars up to z~7 tell us that massive black holes (MBHs) were already in place, with masses well above 10^9 solar masses, when the Universe was less than 1 Gyr old. According to Soltan’s argument and the evolution of the quasar luminosity function, MBHs gain most of their mass via radiatively efficient accretion, hence we expect they formed early in the Universe as smaller seeds. To date, the common formation mechanism advocated to explain the most massive MBHs at high redshift is the direct collapse scenario, which leads to the formation of seed MBHs of about 10^4-5 Msun. However, because of the peculiar conditions required by this formation mechanism, its plausibility is still debated. After highlighting the main conditions required by this scenario, I will discuss whether the peculiar environment in which high-redshift massive galaxies evolve provides ideal conditions for the formation of such massive seeds, and the processes that may potentially inhibit the process. I will also discuss the subsequent evolution of these protogalaxies and their central MBHs up to the observed masses, the importance of the galaxy-BH interaction, and how the MBH obesity found by observations is not necessarily real.

Tues April 5th, 4pm,  Zoom: Luca Cortese (ICRAR) Recording

Galaxy Transformation in the Local Universe

Tues April 12th, 11am,  Zoom: Tim Davis (Cardiff U.) Recording

Tracing out the darkness with cold gas: dynamically probing galaxy evolution: In this talk I will describe how mapping the dynamics of gas clouds in the centre of galaxies can help us to constrain a wide range of astrophysical problems. From the enigmatic relation between galaxies and their supermassive black holes, to the suppression of star-formation in dying galaxies, the dynamics of cold gas provides an ideal probe that can help us make progress. I will show how parsec resolution observations can be used to estimate the masses of supermassive black holes in galaxies across the Hubble sequence, and describe the WISDOM project, that aims to use this technique to constrain the importance of accreting SMBHs in galaxy quenching. I will go on to show that, contrary to expectations, molecular gas appears to be an important source of fuel for accretion in even low-luminosity, low-excitation active SMBHs. Finally, I will show that the deep potential wells of massive galaxies change the small-scale structure of the ISM, suppressing star formation, and helping to keep these objects quenched.

Tues April 26th, 11am,  Zoom: Chris Matzner (U. of Toronto) Recording

Astronomy in the Anthropocene: Rapid climate change, due primarily to burning fossil fuels, poses existential risks to humanity and the world’s ecosystems that demand a swift transition in all aspects of society.   As the most public-facing and publicly-engaged of sciences, astronomy bears a special responsibility to proactively face these complex challenges.   How should researchers and institutions respond?  I will highlight some emerging answers to this question.  I will also argue that being open-eyed about the forces shaping public perception and government policy, and bringing this perspective into our education, outreach, and communications, is just as important as curtailing our professional climate impacts.

Tues May 3rd, 11am,  Zoom: Shantanu Basu (Western U.) Recording

Supermassive Black Holes: The Mass Function and a Formation Channel: One of the ideas to explain the existence of supermassive black holes (SMBH) that are in place by z ~ 7 is that there was an earlier phase of very rapid accretion onto direct collapse black holes (DCBH) that started their lives with masses ~10^5 M_solar.  Working in this scenario, we show that the mass function of SMBH after a limited time period of growing formation rate paired with Eddington or super-Eddington accretion can be described as a broken power-law with two characteristic features. These features identify the growth rate and duration of the DCBH era. A lingering concern about the DCBH scenario however is the angular momentum barrier.  Using a set of three-dimensional magnetohydrodynamic (MHD) simulations, we show that the magnetic field efficiently extracts angular momentum from accreting gas and also enhances the coalescence rate of fragments. Almost all the fragments coalesce to the primary star. We conclude that the magnetic field strongly aids the direct collapse scenario of supermassive star formation.

Tues May 31st, 11am,  Zoom: Aaron Yung (NASA Goddard) Recording

Paving the way for JWST and Roman with Theory and Simulations:
NASA’s JWST and Roman will be the observation powerhouse of the 2020s and will help us see deeper and wider into the high-redshift Universe. In order to maximize their survey efficiency and scientific capabilities, theoretical models and simulations play an important role in forecasting the magnitude, number density, and spatial distribution of expected sources. Furthermore, these physical models are also essential to the interpretation of their intrinsic properties and physical origins. In this seminar, I will showcase the wide range of predictions and data products to be released with the two upcoming papers in the Semi-analytic forecasts series. I will also highlight some of the galaxy formation physics that are expected to be constrained by upcoming observations. These predictions are made with the well-established Santa Cruz semi-analytic model (SAM) and have been shown to perform extremely well at reproducing a variety of observed constraints for galaxies and AGN observed in the past. I will also give a brief demonstration on how they are used in the planning of upcoming JWST galaxy surveys and how to gain access to these publicly available datasets.

Tues June 7th, 4pm,  Zoom: Kathryn Grasha (ANU) Recording

Non-solar scaled abundances for massive stars: the chemical abundance breakthrough for galaxy evolution
Measuring the chemical history of galaxies is critical to understand how galaxies form and evolve. Previously, stellar evolution synthesis relied on databases of the evolution of stars that were based on outdated catalogs of the abundances of chemical elements in stars scaled to Solar that are inconsistent with modern observations of stars and galaxies. To achieve a self-consistent, robust picture of how the distribution of the metals in stars are recycled into the interstellar gas of galaxies throughout cosmic time, I will present my latest work which is providing a breakthrough in this area by creating new stellar tracks with modern abundance sets and combining these tracks with stellar evolutionary synthesis models to create stellar spectra for a broad range of chemical abundances. This represents the first and largest library of theoretical galactic spectra computed self-consistently in all physical input properties from stellar, atmosphere, and photoionisation modelling. These models are based on observed metal abundances in local HII regions which allows us, for the first time, for us to accurately compare stellar observations against models that are not constrained solely against a single star, the Sun. These new stellar tracks and spectra are tailored for the earliest galaxies in the universe based on the latest models of the chemistry elements in early universe galaxies and will enable fundamental new measurements of the formation of stars in the first galaxies.

Fall/Winter 2021

Tues September 28th, 11am,  Zoom: Ting Li (U. of Toronto) Recording

The Southern Stellar Stream Spectroscopic Survey: Overview and Latest Science Results: The Southern Stellar Stream Spectroscopic Survey (S5) is an ongoing spectroscopic program that maps the newly discovered stellar streams with the fiber-fed AAOmega spectrograph on the Anglo-Australian Telescope (AAT). S5 is the first systematic program pursuing a complete census of known streams in the Southern Hemisphere, providing a uniquely powerful sample for understanding the building blocks of the Milky Way’s stellar halo, the progenitors and formation of stellar streams, the mass and shape of the Milky Way’s halo, and ultimately the nature of dark matter. The survey started in Summer 2018 and has mapped ~20 streams with over 50 nights on AAT. In this talk, I will give a brief overview of the current status of the program, highlighting the latest science results from the survey, and end the talk with the first public data release of S5. The science results from S5 cover a wide range, including the finding of a stream perturbed by the dark matter subhalos, the confirmation of a globular cluster stream that is more metal-poor than any known Milky Way globular clusters, the constraints on the mass of the Large Magellanic Cloud with stellar streams, and the discovery of the fastest hyper velocity stars ejected from Galactic center, etc.

Tues October 5th, 11am, Zoom: Allison Kirkpatrick (U. of Kansas) Recording

The Mysterious Growth of Cold Quasars: All galaxies host a supermassive black hole at their centers, at least a million times the mass of the Sun. Material falling onto these monsters can be as bright as the galaxy itself, or it may be lurking unseen behind thick blankets of dust. These monsters go through growth spurts and feeding frenzies that can greatly impact their host galaxies, possibly even terminating all nearby star formation. I will focus on Cold Quasars, which are some of the most luminous accreting black holes in the universe, and yet, surprisingly, their host galaxies have star formation rates of 1000 Msun/yr, casting doubt on whether black hole feedback impacts star formation at all. I will discuss how Cold Quasars are an anomaly in the current understanding of quasar formation.

Tues October 12th, 11am, Zoom: Andrew Mann (Chapel Hill) Recording

Planetary Systems through Time: Planets are not born in their final state. Before reaching a more mature and stable phase, young planets are sculpted by interactions with their host star, other planets in the system, and their greater environment. Large populations of mature (>1 Gyr) exoplanets, like those from the Kepler mission, provide useful but indirect constraints on the relative importance of such evolutionary processes. Because the first few hundred million years of a planet’s life are the most formative, studies of young (<<1 Gyr) planets yield more direct information of exoplanet evolution as they offer the chance to observe such processes in action. However, young planets are also some of the most difficult to identify and characterize. K2 and TESS combined with new search methods have changed the situation by enabling the discovery of transiting planets in 10 — 700 Myr clusters, moving groups, and star-forming regions. The statistical properties of these systems demonstrate that young planets are larger than their older counterparts and provide insight into the timescales of planetary migration. With the extended TESS mission, we can build on this by identifying young planets around bright stars that are amenable to studies of their atmospheres with JWST.

Tues October 26th, 11am, Zoom: Melanie Habouzit (MPIA) Recording

Massive Black Holes: Massive black holes of million solar mass and above are commonly hosted by massive galaxies, but are also present in local dwarf galaxies. Black holes are a fundamental component of galaxies and galaxy evolution, but their origin is still far from being understood. Large-scale cosmological hydrodynamical simulations are crucial to understand massive black hole growth and their interplay with their host galaxies. We recently compared the black hole population of six of these simulations and I will review how the simulation sub-grid models affect the build-up of the black hole population and their correlations with galaxies properties. The next two decades will be dedicated to the exploration of the high-redshift Universe with upcoming space missions such as JWST, Athena, LynX, Roman, and LISA. I will present how we can use cosmological simulations to prepare these missions and maximize their scientific return.

Tues November 2nd, 11am, Zoom: Jonelle Walsh (Texas A & M) Recording

The Supermassive Black Hole – Galaxy Connection: Over the past 20 years it has become increasingly clear that supermassive black holes are essential components of galaxies, as demonstrated by the correlations connecting black hole masses and large-scale galaxy properties. Although about ~100 dynamical black hole mass measurements have been made to date, the local black hole mass census is highly incomplete. Gaining a more complete picture of black hole demographics and a deeper understanding of the mechanisms that drive black hole – galaxy co-evolution requires the measurement of black holes in a wider range of galaxy types with diverse evolutionary histories. In this talk, I will describe a Gemini Large and Long Program aimed at addressing a bias in the types of galaxies for which black hole mass measurements have been made. I will also discuss an ALMA program where we are obtaining gas-dynamical black hole mass measurements for massive early-type galaxies, including a population of local galaxies that show remarkable similarities to galaxies observed at earlier epochs in the Universe.

Tues November 9th, 11am, Zoom: Kathryn Neugent (U. of Toronto) Recording

The Binary Fraction of Red Supergiants … and Beyond!: The binary fraction of massive main-sequence OB stars is thought to be as high as 70% or greater. However, until recently, only around a dozen binary red supergiants (RSGs) had been identified, despite the fact that these stars are the evolved descendants of a large portion of OB stars. My research focuses on searching for these “missing” binary RSGs. As dictated by stellar evolution, binary RSGs will likely have B-type companions and such systems will have unique photometric signatures due to the shape of their spectral energy distributions. After observing candidate RSG+B star binaries spectroscopically in the Local Group galaxies of M31, M33 and the Magellanic Clouds, we’ve discovered over 250 new systems. In this talk I’ll discuss how these results have allowed us to place constraints on the binary fraction of RSGs as a function of metallicity, and the greater impacts this has on our understanding of massive star evolution, supernovae populations, and the creation of gravitational wave events.

Tues November 23rd, 9am, Zoom: Irene Pintos-Castro (U. of Toronto) Recording

Clusters of Galaxies: studying environment & evolution: Galaxy clusters are the largest gravitationally bounded objects in the Universe, which makes them useful cosmological probes, but also great laboratories to study galaxy evolution. They host hundreds of galaxies belonging to two different populations: the red passive sequence and the blue star-forming (SF) cloud. We studied the SF population of galaxies within a sample of ∼200 IR-selected galaxy clusters at redshift 0.3 to 1.1 in two SpARCS fields, exploiting data from the deep layer of the Hyper Supreme-Cam Subaru Strategic Program (HSC-SSP). We observed an accelerated growth of the quiescent population within the cluster environment and found that environmental and mass quenching efficiencies depend on galaxy stellar mass and distance to the centre of the cluster, indicating that the two effects are not separable in the cluster environment. Here, we demonstrated how the large area and depth of these data allowed us to analyze the dependence of the SF fraction on stellar mass and environment separately. However, to deepen further into the effect of the environment, a larger sample is needed. Within this context I will introduce the Observatorio Astrofisico de Javalambre (OAJ) and its main surveys: J-PLUS and J-PAS.

Tues November 30th, 11am, Zoom: Matthew Quenneville (Berkeley) Recording

Measuring Supermassive Black Hole Masses with Triaxial Orbit Modelling: Massive elliptical galaxies have been found to host some of the largest supermassive black holes (SMBHs) in the nearby universe. Accurate dynamical measurements of these black holes are essential for determining the local SMBH-galaxy scaling relations which underpin our understanding of SMBH masses throughout the universe. Of the small number of galaxies that have been modelled while allowing for triaxial shapes, several have shown SMBH mass estimates that are dramatically different from those determined using axisymmetric models. I will discuss the dynamics of stars within a triaxial galaxy and our recent progress in advancing a triaxial orbit code. Together with a novel grid-free sampling technique, we can now efficiently search the high-dimensional parameter space to determine a galaxy’s SMBH mass, stellar mass-to-light ratio, dark matter content, and 3D intrinsic shape simultaneously.

Tues December 7th, 11am, Zoom: Rebecca Bowler (Oxford) Recording

Bright galaxies in the first billion years: Studying galaxies at ultra-high redshifts (z > 6) provides a unique insight into the early stages of galaxy formation and evolution. I will give an overview of how star-forming ‘Lyman-break’ galaxies are selected in the first few billion years. I will then show how samples of these objects can constrain the astrophysics at play in early galaxy formation through the observed shape and evolution of the luminosity function. Finally I will present some of the first resolved measurements of the young stars and dust within normal galaxies in the Epoch of Reionization. These results give a sneak preview of the exciting discoveries upcoming from JWST, as well as Euclid and Roman, on the earliest stages of galaxy formation and evolution.

Tues December 14th, 11am, Zoom: Laurie Rousseau-Nepton (CFHT) Recording

SIGNALS: Learning on the Birth of the Stars with SITELLE: October 2018 marked the beginning of a new large program at the Canada-France-Hawaii Telescope: SIGNALS, the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey. During the next four years and with 60 nights of telescope time in hands, our collaboration is observing more than 50,000 extragalactic star-forming regions located in different galactic environments using the instrument SITELLE, a Imaging Fourier Transform Spectrograph. In order to build this sample, we cover 40 galaxies that are actively forming stars within a distance of 10 Mpc. SITELLE was build in Canada and is the perfect instrument to survey these often extended objets. With SIGNALS, we are seeking to increase our knowledge on how stars form in galaxies, how their birthplace affects their properties, and how multiple generations of stars transform galaxies. Stars continuously affect their environment by returning new elements to the interstellar gas. These new elements are then recycled to form new stars. Stars form in a wide variety of environments. These can be different galaxy to galaxy, location to location. The result is that each star has its own story. By studying 50,000 regions where stars actively form, we will understand what triggers their formation, how efficiently stars form, and how each generation transforms the gas around them. This will also help researchers to understand the star-formation history of the whole Universe since the Big-Bang. During this presentation, I will introduce this ambitious project and the instrument SITELLE as well as show some preliminary results.

Spring/Summer 2021

Tues March 23rd, 11am,  Zoom: Meredith Macgregor (U. of Colorado Boulder) Recording

How to Form a Habitable Planet: More than 20% of nearby main sequence stars are surrounded by debris disks, where planetesimals, larger bodies similar to asteroids and comets in our own Solar System, are ground down through collisions.  The resulting dusty material is directly linked to any planets in the system, providing an important probe of the processes of planet formation and subsequent dynamical evolution.  The Atacama Large Millimeter/submillimeter Array (ALMA) has revolutionized our ability to study planet formation, allowing us to see planets forming in disks and sculpting the surrounding material in high resolution.  I will present highlights from ongoing work using ALMA and other facilities that explores how planetary systems form and evolve by (1) connecting debris disk structure to sculpting planets and (2) understanding the impact of stellar flares on planetary habitability.  Together these results provide an exciting foundation to investigate the evolution of planetary systems through multi-wavelength observations. 

Tues March 30th, 11am, Zoom: Hanno Rein (U. of T) Recording

Chaos, Instability, and Machine Learning: We have known the equations which determine the trajectories of planets for over 300 years. Yet, the long term evolution of the Solar System was not well understood until just a few years ago. In this talk, I will explain why it is so hard to solve these differential equations and describe the recent algorithmic breakthroughs that have made such problems tractable. These new numerical tools allow us to address many exciting scientific questions. I will outline some of my current research projects which aim to improve our understanding of planet formation in our galactic neighbourhood, and put constraints on General Relativity on timescales of billions of years. I will also present how we construct a Bayesian neural network to accurately predict instabilities orders of magnitudes faster than was possible before. This model enables us to include stability constraints in data reduction pipelines for extrasolar planetary systems.

Tues April 6th, 11am, Zoom: Tuan Do (UCLA) Recording Unavailable

The Galactic Center: a laboratory for the study of the physics and astrophysics of supermassive black holes: The center of the Milky Way hosts the closest supermassive black hole and nuclear star cluster to the Earth, offering us the opportunity to study the physics of supermassive black holes and their environment at a level of detail not possible elsewhere. I will discuss 2 major questions that are at the forefront of Galactic center research: (1) What is the nature of the near-infrared emission from Sgr A*? and (2) How do nuclear star clusters form and evolve in the vicinity of a supermassive black hole? I will show how the long time-baseline of Galactic center observations, improved instrumental capabilities, and use of statistical methods to combine many types of data have led us to new insights into these questions. I will discuss what we have learned in 20 years of observations of the supermassive black hole, Sgr A*, in the near-infrared and its surprising increase in activity in recent years. I will also discuss how the results the first chemical-dynamical model of the Milky Way Nuclear Star Cluster allow us to disentangle its complex formation.

Tues April 13th, 11am, Zoom: Deep Anand (U. of Hawaii) Recording

Tues April 20th, 11am, Zoom: Auriane Egal (Western U.) Recording

Comet Halley’s twin meteor showers: 1P/Halley is a famous comet that aroused the interest of the general public and the scientific community for several centuries. Its most recent apparition in 1986 motivated an unprecedented observational effort, combining spacecraft rendezvous and ground-based telescopic programs led by different countries. Most of our knowledge about the comet’s activity and evolution comes from the results of this exceptional observation campaign. From the analysis of ancient Chinese and Babylonian inscriptions, we suspect that 1P/Halley has been delivering meteoroids to Earth for several millennia. In particular, the comet is known to produce two meteor showers at the present epoch, the Eta-Aquariids in May and the Orionids in October. However, and despite decades of meteor observations, most of the showers’ characteristics are still unexplained. In this presentation, we expose the results of a new numerical model of 1P/Halley’s meteoroid streams, allowing to reproduce the meteor showers’ formation, intensity, duration, and predict the apparition of future meteor outbursts to watch. In particular, we expect three Eta-Aquariids outbursts in the future that deserves special attention.

Tues April 27th, 11am, Zoom: Oliver Müller (U. of Strasbourg) Recording

A cosmic ballet of dwarf galaxies as challenge for dark matter cosmology: Dwarf galaxies are not only the most common galaxies but also the most dark matter dominated objects in the universe. By studying their abundance and distribution, we can test our current model of cosmology. Around the Milky Way and the Andromeda – the Local Group –, several discrepancies between observations and the predictions for these dwarf galaxies have been identified, constituting a small-scale crisis. The most severe of them is the plane-of-satellites problem: the dwarf galaxy satellites around the Milky Way and the Andromeda are aligned in thin, planar, co-rotating structures. This is in stark contrast to the results of cosmological simulations, where for the satellite system an isotropic distribution with random motions is expected. This raises the question: Is the Local Group unique? Recent observations of the nearby Centaurus group say it is not. In my talk, I will give a review over the current state of this peculiar question in near-field cosmology.

Tues May 4th, 11am, Zoom: Judit Prat (DES/U. of Chicago) Recording

Galaxy-galaxy lensing and Lensing Ratios for Cosmological Analyses in the Dark Energy Survey: Galaxy cosmic surveys such as the Dark Energy Survey are a powerful tool to extract cosmological information. In particular, the combination of weak lensing and galaxy clustering measurements, usually known as 3x2pt, provides a potent and robust way to constrain the parameters controlling the structure formation in the late Universe. Galaxy-galaxy lensing, which is the cross-correlation of the shapes of source background galaxies with lens foreground galaxy positions, is one of the three probes that is part of this combination. In this talk, I will describe how we can accurately measure and model galaxy-galaxy lensing correlations using the well-understood large scales with the purpose of extracting cosmological information. Besides this, I will also describe how we can construct suitable ratios of these measurements to exploit the otherwise usually disregarded small-scale information and naturally integrate it as a part of the 3x2pt analysis.

Tues May 25th, 11am, Zoom: Carl Fields (MSU/Arizona/LANL)  Recording

Next-Generation Simulations of The Remarkable Deaths of Massive Stars: Core-collapse supernova explosions (CCSN) are one possible fate of a massive star. Simulations of CCSNe rely on the properties of the massive star at core-collapse. As such, a critical component is the realization of realistic initial conditions. Multidimensional progenitor models can enable us to capture the chaotic nuclear shell burning occurring deep within the stellar interior. I will discuss ongoing efforts to progress our understanding of the nature of massive stars through next-generation hydrodynamic stellar models. In particular, I will present recent results of three-dimensional hydrodynamic massive star models evolved for the final 10 minutes before collapse. These recent results suggest that realistic 3D progenitor models can be favorable for obtaining robust models of CCSN explosions and are an important aspect of massive star explosions that must be taken into consideration. I will conclude with a brief discussion of the implications our models have for predictions of multi-messenger signals from CCSNe.

Tues June 1st, 11am, Zoom: Yamila Miguel (Leiden) Recording

Unveiling the secrets of Jupiter with the Juno mission: With more than 4000 exoplanets found and about 2-dozens of planets with detected atmospheric chemical species, we moved from an era of discovery to a new era of exoplanet characterisation. On the other hand, extremely accurate measurements by Juno and Cassini missions, make this an exceptional time to combine the detail information on the solar system giant planets and the large amount of data from exoplanets to get a better understanding on planetary physics and a better comprehension on planet formation and evolution. Because our knowledge on the interior structure of the giant planets is linked with the data we obtain from space missions, these last years were crucial for this field: the outstanding accuracy of the gravity data provided by Juno has fundamentally changed our understanding of the interior of Jupiter. It has allowed us to put constrains on the zonal flows, the extent of differential rotation and lead us to find that Jupiter has most likely a dilute core. In this presentation I will review our knowledge on the interior structure of Jupiter and will also show some new results where we find that a non-homogenous envelope is also a constraint set up by the Juno measurements, which is helping us to get closer to unveiling Jupiter’s deep secrets and to reach a better understanding of the giant planets formation history.

Tues June 8th, 11am, Zoom: Shany Danieli (IAS) Recording

Towards a better understanding of low mass galaxies beyond the Local Group: Low mass galaxies provide an essential testing ground for theoretical predictions of cosmology. Their number densities, structures, and internal dynamics can be extremely insightful for studying dark matter and galaxy formation on small scales. I will discuss recent results studying dwarf galaxies and ultra-diffuse galaxies (UDGs). UDGs hold the promise of new constraints on low mass galaxies dynamics, as their spatial extent and often significant globular cluster populations provide probes on spatial scales where dark matter should dominate the kinematics. I will also discuss the dynamics of two UDGs that seem to lack most, if not all, of their dark matter and host an intriguing population of globular clusters. I will finish by presenting a new wide-field survey carried out with the 48-lens Dragonfly Telephoto Array. With an excellent photometric depth, the Dragonfly Wide Field Survey will provide an unprecedented view of the low surface brightness universe over a wide area of the sky (350 square degrees). The main goal of the survey is to provide information on the properties and statistics of the dwarf galaxy population beyond the Local Group but it will also provide a useful resource for other resolved, low surface brightness phenomena, such as stellar streams and tidal tails, stellar halos, intragroup light and the extent of massive galaxies.

Tues June 22nd, 11am, Zoom: Jane Huang (U. of Michigan) Recording

The ALMA View of Planet Formation: The ubiquity and diversity of planets tell us that they can emerge under an astonishing range of conditions. By enabling us to map the distributions of dust grains and molecules in protoplanetary disks at an unprecedented level of detail, the Atacama Large Millimeter/Submillimeter Array (ALMA) has transformed our understanding of planet formation. In the Disk Substructures at High Angular Resolution Project (DSHARP), we undertook the first high angular resolution disk survey at millimeter wavelengths. Although protoplanets are difficult to detect directly, the widespread presence of dust gaps and rings in disks suggests that giant planet formation may occur readily on Myr-timescales at surprisingly wide separations. Meanwhile, in a small but growing number of systems, detections of puzzling spiral structures oblige us to re-examine common assumptions about the reservoir of material available for planet formation. ALMA has also revealed strong chemical heterogeneity within and among disks, laying the observational groundwork for linking the compositions of planets to their formation location. Together, these new data show that the natal environments of planets are far more dynamic and varied than earlier observations have indicated. 

Winter 2021

Tues January 19th, 11am, Zoom: Kim-Vy Tran (UNSW) Recording

MOSEL & ZFIRE : Tracking Galaxy Growth at Cosmic Noon: MOSEL and ZFIRE are deep near-IR spectroscopic surveys that track how galaxies assemble at 1.5<z<3.5. With MOSEL, we confirm a population of Extreme Emission Line Galaxies at z~3 with Oxygen equivalent widths >250 Angstroms and hypothesize that most galaxies at z>3 go through a strong starburst phase. We compare galaxy kinematics to IllustrisTNG to determine how massive galaxies at z~3 build their stellar mass (mostly by accreting other galaxies) and end their star formation (puffy galaxies quench slower). I also summarize results from our ZFIRE survey where we find faint imprints of environmental effects on the Inter-Stellar Medium of cluster galaxies at z~2.

Tues January 26th, 4pm***, Zoom: Takuma Izumi (NAOJ)   Recording

ALMA observations of z > 6 low-luminosity quasars: unbiased view on the early co-evolution and feedback: I will review our multi-wavelength campaign observations toward z > 6 optically “low-luminosity” quasars, which were originally discovered by our wide-field Subaru Hyper Suprime-Cam (HSC) optical imaging survey. Our HSC quasars are an order of magnitude fainter at rest-UV than previously-known luminous quasars. Subsequent NIR spectroscopic follow-up observations revealed a wide spread in their BH mass, hence Eddington ratio (~0.1 to 1). We have also been carrying out a series of ALMA observations ([CII] line and FIR continuum emission) toward a sample of ~20 HSC quasars. We found that their host galaxies are basically FIR-faint with LIRG-class luminosities (or SFR < 100 Msun/yr). Using the [CII]-based dynamical mass as a surrogate for bulge stellar mass, we found that a significant fraction of these low-luminosity quasars are located on or even below the local co-evolution relation, indicating the BH-galaxy co-evolution is indeed taking place at z > 6. I also talk about a particular case of a z = 7.1 HSC quasar, where we found a vigorous starburst and, surprisingly, fast [CII] outflows. Given also its broad absorption line = BAL feature  (indication of nuclear outflow), quasar-driven feedback that affects the host galaxy occurred already at this reionization era.

Tues February 2nd, 11am, Zoom: Ilse Cleeves (U. of Virginia) Recording

The key role of astrochemistry in driving planet formation and habitability: Historically, our perspective on how planets form and obtain their compositions has been motivated by our Solar System. However, we are just one system, and missions like Kepler and TESS have revealed a variety of planetary types and architectures. How do we fit in? In the last five years, the Atacama Large Millimeter Array has revolutionized our understanding of planet formation by observing the process at high spatial resolution (reaching in some cases ~AU scales) matched with unprecedented sensitivity at radio wavelengths. In this presentation, I will review recent highlights from the TW Hya as a Chemical Rosetta Stone ALMA project and discuss how these findings both confirm and, in some ways, challenge our current picture of the chemistry of planet formation.

Tues February 16th, 11am, Zoom: Genaro Suarez (Western U.) Recording

An Accurate Look at the L-to-T Spectral Type Transition: I will present the most comprehensive spectral energy distribution (SED) of a young brown dwarf at the L/T transition by combining new Spitzer mid-infrared spectra and photometry with previous observations of HN Peg B. We use this SED to evaluate the performance of various atmospheric models and found that models with condensates and using non-equilibrium chemistry reproduce better the data. However, these models face challenges in reproducing the observed methane and carbon monoxide absorption strengths mainly over the 3–5 um region. By using the assembled SED and the Gaia EDR3 parallax of the host star, we derive accurate fundamental parameters of HN Peg B. We find that, in comparison to older early T dwarfs in the field, HN Peg B is ≈100 K cooler, has a ≈ 13% larger radius, and has a consistent bolometric luminosity. A comparison among moderate-dispersion near-infrared spectra of HN Peg B and other young and old dwarfs with similar spectra types shows that the 1.25-micron potassium line strengths are mostly insensitive to surface gravity in early-T dwarfs.

Tues February 23rd, 3pm***, Zoom: Emily Wisnioski (ANU) Recording

The resolved dynamics and metallicity of galaxies across cosmic time: I will discuss the formation and evolutionary paths of star-forming galaxies. Kinematics and chemical properties have revealed that the majority of star-forming galaxies at ‘comic noon’ host thick disk-like structure and a turbulent less enriched interstellar medium. I will present results utilising synergies with multi-wavelength ground and space-based surveys to trace the evolution of spatially-resolved dynamics and star formation from a homogeneous sample over 5 billion years of cosmic history. These results when combined with local galactic archeology studies and new analytic models provide insights into how the structures of local galaxies including the Milky Way were formed. I will discuss the observational results within the framework of theoretical models for the formation of gas phase metallicity gradients and the local stellar age-velocity dispersion relation.

Tues March 9th, 11am,  Zoom: Laura Keating (AIP) Recording

Insights into the epoch of reionization from quasar absorption lines: The epoch of reionization marks the last major phase transition of the Universe, when photons emitted by the first structures ionized and heated the gas surrounding them. A complete understanding of reionization would reveal the properties of the first stars and galaxies, as well as increasing the precision to which the high-redshift intergalactic medium can be used to constrain cosmological parameters. In this talk I will demonstrate that the the pattern of absorption lines seen in distant quasars, known as the Lyman-alpha forest, is an ideal tool to study reionization. I will present results from cosmological radiative transfer simulations, which were carefully calibrated to reproduce the statistics of the Lyman-alpha forest, and will show that matching the observations requires reionization to have ended much later than previously thought.

Tues March 16th, 1pm***, Zoom: JJ Eldridge (U. Auckland) Recording

Some of the things binary stars do…. Most of the stars in the Universe are not single like our Sun but in binary stars systems. A binary star is composed of two stars in orbit around each other, as they age they can “get-in-each-others” way and experience very different evolution to that our stars like our Sun. Only over the last decade it has become clear that to accurately understand the Universe we need to take account of these interacting binary stars. In my talk I will go over a few examples showing how understanding binary stars allows us to understand the appearance of galaxies, the diversity of supernovae, the production of the most abundant and rarest elements and discuss the latest LIGO/VIRGO O3a results and their implications for binary evolution.

Fall 2020

Tues September 15th, 11am, Zoom: Silvia Toonen (U. of Birmingham) Recording

Stellar interactions and transients: In order to understand the Universe we live in, we must understand the diverse lives of stars, the fundamental building blocks of galaxies and stellar clusters. However, most stars do not evolve in isolation; they have one or more stellar companions that they can interact with. These interactions give rise to some of the most energetic events in the universe, e.g. stellar mergers, supernovae Type Ia explosions and gravitational wave sources. The last decade has revealed the existence of a large and diverse zoo of transients, but their origin or progenitor evolution is often unknown. In this talk I will show novel channels to induce stellar interactions and subsequent transients. I will present our latest results regarding the evolution of white dwarf binaries and their mergers, with implications for Galactic archaeology. Secondly, I will discuss how triple stars can evolve differently from binary stars, and show their potential as transient progenitors. While triple star systems are common, our understanding of their evolution has lagged behind compared to single and binary stars. I will conclude with revealing a new primary channel of binary evolution towards supernova type Ia events.

Tues September 22nd, 11am, Zoom: Fabio Pacucci (Harvard)  Recording

Detecting the Dawn of Black Holes: In this talk I discuss the quest to unravel two undetected populations of high-z black holes. The first population of black holes formed when the age of the Universe was less than 500 Myr, while by z=7 we have observations of fully-fledged, shining quasars. Shedding light on this cosmic period is one of the key tasks that the astronomical community will focus on in the next decade, due to its crucial importance for the early evolution of the Universe.The observational signatures of black hole seeds remain largely unexplored, and we are yet to detect these sources. I present detailed predictions for the spectra of different categories of seeds, and a photometric method to identify them in surveys. I explore the role that future facilities (e.g., JWST, Athena, Lynx, LISA) will play in this quest, by detecting both black hole accretion and mergers. To conclude, I show a detailed analysis of the requirements and the expectations for a comprehensive search of z > 10 black hole seeds. Moving at slightly lower redshifts, the discovery of the first strongly lensed quasar at z > 6 (J0439+1634, Fan et al. 2018) represents a breakthrough in our understanding of the early Universe. Pacucci & Loeb (2018) predict that the observed population of z > 6 quasars should contain many mildly magnified sources, with image separations below the resolution threshold. Additionally, current selection criteria should have missed a substantial population of lensed z > 6 quasars: WFIRST will likely play a crucial role in revealing this population. I estimate the fraction of undetected quasars as a function of the slope of the bright end of the quasar luminosity function. For steep values of this parameter, the vast majority of the z > 6 quasar population is lensed and still undetected. These “phantom quasars” would be misclassified and mixed up with low-z galaxies. I conclude by addressing how gravitational lensing can affect the inferred black hole mass distributions at z > 6, possibly having important implications for current theories of growth for early quasars.

Tues September 29th, 11am, Zoom: Benne Holwerda (U. of Louisville) Recording

A Search for High-Redshift Galaxies And An Accidental Galactic Survey of Dwarf Stars with Hubble: Current searches for high-redshift galaxies use a combination of near-infrared filters with one or more optical filters to check for contaminants. One of these contaminants are faint dwarf stars in the disk and halo of our own Milky Way Galaxy. Thus in the search for the galaxies that caused the Reionization of the Universe, an accidental census of Dwarf stars in the Milky Way was conducted as well. I report on one observational approach with the Hubble Space Telescope; the Brightest Origin of Reionizing Galaxies (BORG) survey. I will discuss the identification of the distant high-redshift galaxies, their unique properties, the faint brown and red dwarf stars (M-dwarfs) and our results on characterizing the shape of the Milky Way from their number. We identified stellar objects in the BoRG survey and mapped their distribution onto the Milky Way. Results are a thin disk (300pc), the rediscovery of the Sagittarius stream, a total count of 58 billion M-dwarfs in the Milky Way of which 7% reside in the halo. We also found a population of very bright, redshift eight galaxies (“Super-Eights”) that show evidence for strong nebular emission lines and direct observations of Lyman-alpha. The Super-Eights appear to reveal a very specific mode of star-formation that may have played a critical role in the Reionization of the Universe.

Tues October 6th, 11am, Zoom: Vivienne Baldassare (Washington State U.) Recording

Searching for active galactic nuclei in low-mass galaxies via optical variability:  The present-day population of supermassive black holes in low-mass galaxies offers a window into massive black hole formation in the early universe. While we cannot yet observe the formation of “black hole seeds” at high redshift, the fraction of small galaxies that host a supermassive black hole — and the properties of those black holes — are thought to depend on the mechanism by which these they form. However, black holes in the smallest galaxies can be difficult to find, requiring creative new approaches. I will discuss recent work showing that long-term optical photometric variability in low-mass galaxies can identify active galactic nuclei that are missed by other selection techniques. I will present an analysis of the nuclear variability of more than 70,000 nearby galaxies and discuss our sample of low-mass, variability-selected supermassive black holes. Using this sample, we are also able to place meaningful constraints on the present-day black hole occupation fraction at low galaxy stellar masses. 

Tues October 13th, 3pm***, Zoom: Madeline Marshall (HAA) Recording

The Host Galaxies of High-Redshift Quasars: Studying the host galaxies of high-redshift quasars provides vital insights into the early growth of supermassive black holes and the black hole—galaxy connection. Here I present an analysis of the properties and environments of the host galaxies of z=7 quasars from the BlueTides hydrodynamical simulation. I will also show our latest work using HST to obtain upper limits on the UV emission of z~6 quasar host galaxies. In combination, these two techniques will help to pave the way for making the first near-infrared detections of high-redshift quasar hosts with JWST.

Tues October 20th, 11am, Zoom: Greg Mosby (NASA) Recording

Estimating star formation histories from galaxy spectra and the path to life finding NIR detectors: The evolution of galaxies can be conveniently broken down into the evolution of their contents. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. We can use stellar population modeling of galaxies to test galaxy evolution and formation models. However, in the limit of low galaxy surface brightness, integrated spectra often have such low S/N that it hinders analysis with standard stellar population modeling techniques. To address this problem, we have developed a method that can recover galaxy star formation histories (SFHs) from rest frame optical spectra with S/N ~ 5 Å^-1 with a specific application to quasar host galaxies. We use the machine learning technique diffusion k-means to tailor the stellar population basis set, composed of 4 broad age bins, and it is successful in recovering a range of galaxy SFHs. Our method has the advantage in recovering information from quasar host galaxies and could also be applied to the analysis of other low S/N galaxy spectra such as that typically obtained for high redshift objects and integral field spectroscopic surveys. I have now begun using diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. In addition, I have begun work to fully characterizing today’s HgCdTe photodiode arrays to lay the foundation for future near infrared detector development. Low read noise and well-characterized detectors are crucial in the emerging search for biosignatures in exoplanet atmospheres.

Tues October 27th, 11am, Zoom: Monika Soraisam (U. of Illinois at Urbana-Champaign) Recording

Tues November 17th, 11am, Zoom: Davide Farnocchia (JPL/CalTech) Recording Unavailable

OSIRIS-REx and impact hazard assessment for asteroid (101955) Bennu: The OSIRIS-REx mission is part of NASA’s New Frontiers Program and is the first U.S. mission to retrieve a sample of an asteroid and carry it to Earth for further study. The target of OSIRIS-REx (101955) Bennu, a 500 m near-Earth asteroid that is expected to have organic compounds and water-bearing materials. OSIRIS-REx launched in September 2016 and rendezvoused with Bennu in late 2018. After two years of proximity operations, on 2020 October 20 OSIRIS-REx successfully executed the sample collection sequence and is now preparing for the return cruise to Earth to deploy the sample in 2023. In this talk, I will present the current status of the mission, highlighting some the main challenges faced by the mission and the most relevant scientific results. In particular, I will focus on the impact hazard problem. Bennu is a potentially hazardous asteroid and its trajectory is deterministic until the close approach with Earth in 2135. After this encounter, the orbital uncertainty of Bennu increases to a level that its trajectory can only be analyzed in a statistical sense, and impacts with Earth cannot be ruled out in the second part of the next century. Key to the modeling of Bennu’s trajectory is the Yarkovsky effect, a subtle nongravitational perturbation due to non-isotropic thermal radiation that causes a semimajor axis drift. The OSIRIS-REx tracking data provide useful constraints on this perturbation and on the Bennu hazard assessment.

Tues November 24th, 11am, Zoom: Ian Roederer (U. of Michigan) Recording

The astrophysical r-process: what we are learning from gravitational waves, dwarf galaxies, and stellar archaeology: Understanding the origin of the elements is one of the major challenges of modern astrophysics. The rapid neutron-capture process, or r-process, is one of the fundamental ways that stars produce the heaviest elements, but key aspects of the r-process are still poorly understood. I will describe four major advances in the last few years that have succeeded in confirming neutron star mergers as an important but perhaps not exclusive site of the r-process. These include the detection of freshly produced r-process material powering the kilonova associated with the merger of neutron stars detected via gravitational waves (GW170817), the identification of a dwarf galaxy where most of the stars are highly enhanced in r-process elements (Reticulum II), new connections between the r-process and its Galactic environment (thanks to data from the Gaia satellite), and advances in deriving abundances of previously-undetected r-process elements (such as Se, Te, Pt) in ultraviolet spectra of metal-poor stars. I will highlight opportunities to connect these research directions with future facilities (like FRIB, CETUS, and HabEx) to associate specific physics with specific sites of the r-process.

Tues December 1st, 11am, Zoom: Feige Wang (U. of Arizona)  Recording

Tues December 8th, 11am, Zoom: Stanimir Metchev (Western U.) Recording

Micro- and nano-satellites offer cost-effective platforms for space technology development and for targeted investigations in astronomy: As demonstrated by MOST and BRITE, time-domain photometry of bright objects, such as Milky Way stars and planetary systems, can be well-served by their modest apertures. Improving detector technology is now opening small-sat platforms to fainter extragalactic objects, to non-optical wavelengths, to multi-band photometry, low-resolution spectroscopy, and polarimetry. Two novel opportunities have been explored through recent studies for the CSA. The Photometric Observations of Extrasolar Planets (POEP) mission aims for dedicated UV and near-IR capability on a 15 cm telescope to characterize atmospheric scattering in exoplanetary atmospheres and to detect Earth-sized planets around red dwarfs. POEP has been endorsed as a highly-ranked LRP2020 space astronomy priority in the <$25M category, behind only continued support for JWST. The Extrasolar Planet Polarimetry Explorer (ÉPPÉ) aims to be the first space mission designed specifically for precision polarimetry. Differential polarimetric observations with ÉPPÉ would be sensitive to tenuous amounts of atmosphere on known exoplanets, and in particular to highly-polarizing volatiles, such as water, methane, etc. Both POEP and ÉPPÉ would offer unique capabilities that would complement well the suite of large space telescopes anticipated at the end of this decade. Given Canada’s astronomy small sat heritage, it is in a strong position to lead these new developments.

Summer 2020

Tues May 12th, 11am, Zoom: Evelyn Johnston (Universidad Católica)                  

Tues May 19th, 11am, Zoom: Paul Wiegert (Western University)

Tues June 2nd, 11am, Zoom: Decker French  (Carnegie Observatories),  Recording

Tues June 9th, 11am, Zoom: Raja GuhaThakurta (Santa Cruz/Lick Obs.), Recording

Tues June 16th, 11am, Zoom: Peter Brown (Western University), Recording

Tues June 23rd, 11am, Zoom: Ylva Gotberg (Carnegie Observatories), Recording

Tues June 30th, 4pm**, Zoom: Daniel Price (Monash University), Recording

Tues July 7th, 11am, Zoom:  Meg Schwamb (Queen’s U Belfast), Recording

Tues July 14th, 11am, Zoom: Jan Cami (Western University), Recording

Winter 2020

Tues January 14th, 11am, LCR: Marcin Sawicki (St Mary/HAA)                            

Tues January 21th, 11am, LCR: Jay Melosh (Perdue University)

Tues February 4th, 3pm, LCR: David Hendel  (University of Toronto)

Tues February 11th, 11am, LCR: Brian Svaboda (NRAO New Mexico)

Tues February 18th, 11am, LCR: Sarah Sadavoy (Queens University)

Tues February 25th, 11am, LCR: Gijs Mulders (University of Chicago)

Tues March 3rd, 11am, LCR: Ilse Cleeves (University of Virginia) Cancelled/Postponed due to travel restrictions

Tues March 10th, 11am, LCR:  Daryl Haggard (McGill University)

Tues March 17th, 11am, LCR: Greg Mosby (NASA Goddard) Cancelled/Postponed due to travel restrictions

Tues March 24th, 11am, LCR: Fabio Pacucci (CfA/Harvard) Cancelled/Postponed due to travel restrictions

Tues March 31th, 11am, LCR: Mehrnoosh Tahani (DRAO) Cancelled/Postponed due to travel restrictions

Fall 2019

Tues September 17th, Todd Henry (Georgia State University)

Tues September 24th, Eve Lee (McGill)

Mon October 7th, Satoshi Yamamoto (University of Tokyo)

Tues October 15th Gwendolyn Eadie (University of Toronto)

Tues October 22nd,  Tyrone Woods (HAA)

Tues October 29th, Isabel Santos-Santon (Univeristy of Victoria)

Tues November 5th, Library: Sarah Pearson (Flatiron institute)

Tues November 19th, Jennifer Marshall (MSE)

Tues November 26th, Brian Mason (Georgia State University)

Tues December 3th, Allison Man (Dunlap Institute)

Tues December 10th, Raphaël Errani (University of Victoria/CITA)

Spring 2019

Fall 2018

Spring 2018

Fall 2017

Spring 2017

Fall 2016

Spring 2016

Fall 2015

Spring 2015

Fall 2014

Spring 2014

Fall 2013

Sep 17   Chris Stubbs
Sep 24   Hilke Schlichting
Oct 01   Donald Morton
Oct 08   Helen Kirk (NRC/DAO)
Oct 17   James Bullock (UC Irvine)
Oct 22   Riccardo Giovanelli
Oct 29   Ruben Sanchez-Janssen (NRC/DAO)
Nov 05   Michele Bannister (UVic)
Nov 12   Katherine Alatalo
Nov 19   Nitya Kallivayalil ** cancelled **
Nov 26   Diana Dragomir
Dec 03   Andy Becker
Dec 10   Inger Jorgensen

Spring 2013

Jan 29   Asa Bluck (UVic)
Feb 05   Miguel Morales
Feb 12   Jorge Moreno (UVic)
Feb 19   Erin Bonning
Feb 26   Jonathan Williams
Mar 05   Mike Boylan-Kolchin
Mar 12   Alex Kim
Mar 21   Tony Tyson
Mar 26   David Wilner
Apr 09   Joern Geisbeusch
Apr 16   Wes Traub
Apr 23   Paul Kalas
Apr 25   Yin-Zhe MA
Apr 30   Graca Roca
May 14   Brian McNamara (U. Waterloo)
May 21   Mubdi Rahman

Fall 2012

Aug 28   Andrea Kunder (CTIO)
Sep 04   Jennifer Karr (ASIAA) / Hiro Takami (ASIAA)
Sep 11   No Seminar Scheduled
Sep 18   Nicholas Ball (NRC/DAO)
Sep 25   Chris Reynolds (U. Maryland)
Oct 02   Ben Mazin (UC Santa Barbera)
Oct 09   Matthijs van der Wiel (U. Lethbridge)
Oct 16   Charlie Conroy (UC Santa Cruz)
Oct 23   Sarah Ballard (UW)
Oct 30   Susan Terebey (California State)
Nov 07   Shelley Wright (Dunlap)
Nov 13   Wesley Traub (JPL)
Nov 20   Norman Murray (CITA)
Nov 27   Tim Beers (NOAO)
Dec 04   Tim Robishaw (NRC/DRAO)

Spring 2012

Jan 17   David Tsang (Caltech)
Jan 24   Else Starkenburg (UVic)
Jan 31   Tommaso Treu (UC Santa Barbara)
Feb 07   Federica Bianco (LCOGT)
Feb 14   No Seminar Scheduled
Feb 23   Crystal Martin (UC Santa Barbara)
Feb 28   Scott Schnee (NRAO)
Mar 06   Trevor Mendel (UVic)
Mar 14   Stephen Kane (Caltech)
Mar 22   Peter Yoachim (UW)
Mar 27   Martin Bureau (U. Oxford)
Apr 03   Lynne Jones (UW)
Apr 10   Wes Fraser (NRC/DAO)
Apr 17   John Tobin (NRAO)
Apr 24   James Graham (Dunlap)
May 11   Faith Vilas (U. Arizona)
Jun 11   Giuseppina Battaglia (ESO/INAF)
Jun 14   Jeremy Mould (NOAO)

Fall 2011

Sep 13   Sarah Loebman (UW)
Sep 20   Bob Rood (U. Virginia)
Sep 27   Kate Su (Steward)
Oct 04   Sarah Brough (AAO)
Oct 05   Gary Sanders (TMT Project Manager)
Oct 11   Uma Gorti (SETI)
Oct 17   James Truran (U. Chicago) ** cancelled **
Oct 18   Henrik Beuther (MPIA)
Oct 25   Gregory Sivakoff (U. Alberta)
Nov 01   Steven Allen (Stanford)
Nov 08   Ray Jayawardhana (U. Toronto) ** cancelled **
Nov 15   Pascale Jablonka (EPFL / Observatoire de Paris)
Nov 22   Gunther Hasinger (IfA)
Nov 29   Andrew Youdin (CfA)
Dec 06   Beth Willman (Haverford)
Dec 13   Chung-Pei Ma (UC Berkeley)

Spring 2011

Jan 05   Preethi Nair (U. Toronto/INAF)
Jan 17   Danilo Marchesini (Tufts)
Jan 26   Evgenya Shkolnik (DTM)
Feb 01   Charles Lawrence (JPL)
Feb 08   Cassie Fallscheer (UVic/NRC)
Feb 15   Rita Mann (NRC/DAO)
Feb 22   Ingrid Stairs (UBC)
Mar 08   Matt Walker (CfA)
Mar 15   Ata Sarajedini (U. Florida)
Mar 22   Sean M. Andrews (CfA)
Apr 05   John Dubinski (U. Toronto)
Apr 12   Eric Bell (U. Michigan)
Apr 19   Jon Willis (UVic)
Apr 26   John Carpenter (Caltech)
May 03   Bill McKinnon (St. Louis)
May 10   Richard de Grijs (UPeking/KIAA)

Fall 2010

Sep 14   Emily Schaller (U. Arizona)
Sep 20   Hendrik Hildebrandt (UBC)
Sep 21   Carol Lonsdale & Mark McKinnon (ALMA)
Sep 28   David Jewitt (UCLA)
Oct 05   Meridith Hughes (UC Berkeley)
Oct 07   Ricardo Munoz (Yale)
Oct 12   Mark Booth (Cambridge/DAO)
Oct 19   Jason Rowe (NASA Ames)
Oct 26   Andrew Benson (Caltech)
Nov 02   Lee Hartmann (U. Michigan)
Nov 09   Michele Cantiello (INAF)
Nov 16   No Seminar Schedule (CFHT Users Meeting in Taipei)
Nov 23   Guy Worthey (WSU)
Nov 30   Lisa Kewley (U. Hawaii)
Dec 07   Kristin Woodley (UBC)
Dec 09   James Di Francesco (NRC/DAO)
Dec 14   Sean Dougherty (NRC/DRAO)