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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)