DAO Colloquium Schedule
We have a mixture of fully remote and in person talks. In person talks will take place in the LCR and will also be streamed live online via Zoom.
Tuesdays at 11am unless otherwise indicated with (***)
Archive of previous seminar schedules (2010-)
Upcoming:
Tues. May 27: Yuki Okoda (NRC-HAA), in-person
Dynamic Nature of Early Star Formation
Exploring the early stage of low-mass protostellar evolution is crucial for understanding the processes of star and planet formation, and ultimately, the origin of our solar system. Key questions include: How does a young protostar grow? When does disk formation begin? And how does the disk evolve—both physically and chemically? In this talk, I will present intriguing observational features during the early stage, such as drastic changes in outflow directions in a source with an early disk structure; an accretion shock located outside an expectedly tiny disk; and chemical diversity within disk/envelope systems. These findings suggest that early star formation is more dynamic and complex than previously thought.
Tues. June 10: Akshara Viswanathan (UVic), in-person
Title/Abstract: TBD
Tues. June 17: Bradley Meyers (Curtin University, Perth), in-person
Science with the AusSRC: Building on the Precursors Towards the SKA
The Australian SKA Regional Centre (AusSRC) is Australia’s portion of the international SKA Regional Centre network, which aims to establish and build capability to support the Australian and international SKA science communities, thereby ushering in the next era of astronomical discovery and advanced data processing. In this presentation I will cover the broad and diverse scientific projects that the AusSRC facilitates, with particular focus on our current support for the Australian SKA Precursors, the Murchison Widefield Array (MWA) and the Australian SKA Pathfinder (ASKAP), and several large surveys within the domains of galactic and extragalactic astronomy, fast and slow transients, cosmology, and more. I will cover AusSRC’s future plans to transition into full support of the SKA science, building on top of our experience with the SKA precursors to develop the capabilities essential to facilitating science with the SKA.
— Summer Break in Colloquium Series —
Previous — Spring 2025
Tues. May 20: Alex Riley (Durham University, UK), in-person (Recording — Audio starts at 10:35, sorry. You mostly miss only some introduction material)
The tangled web of disrupting satellites surrounding Milky Way-mass galaxies
Stellar streams provide a record of their host’s merger history and the opportunity to study stellar populations of older, disrupting galaxies. As more of these structures have been uncovered in wide-area digital sky surveys, there has been a push to characterize the full system of tidally disrupting satellites in simulations at Milky Way-mass and smaller scales. I will present my efforts to do so in two regimes: fully hydrodynamical simulations (Auriga) and “painting” stars onto the highest resolution cosmological simulation ever run of a Milky Way-mass halo (Aquarius). These simulations predict that (i) most satellites are disrupting to form faint tidal streams, (ii) many of these streams are detectable in Rubin/LSST-depth photometry, and (iii) most Milky Way satellites have their own accreted stellar haloes formed from mergers with smaller galaxies. These results suggest that upcoming surveys (DESI, LSST, ARRAKIHS) will unlock new tests of dark matter and hierarchical galaxy formation at the smallest scales.
Tues. May 6: Chris Martin (CalTech), in-person (Recording available soon…)
Imaging the Cosmic Web
The intergalactic medium (IGM) represents the dominant reservoir of baryons at high red- shift, traces the architecture of the cosmic web dominated by dark matter, and fuels on-going galaxy evolution. The IGM has been studied using Quasi-Stellar Objects (QSO) absorption lines including the Lyman alpha forest (LAF), which are unable to provide the information that emission maps would give. But because of the low surface brightness and extended, diffuse distribution, direct detection of an emission equivalent to the absorption LAF has not been possible with existing instrumentation and observational approaches. Using a purpose-built instrument, with nod-and-shuffle and dual-field subtraction, we have detected, for the first time, an emission Lyman α forest (ELAF). The emission forest is highly extended, shows filamentary morphology with filaments connecting galaxies, exhibits statistics like the ab- sorption Lyman α forest, displays spectra resembling the absorption forest, and is correlated with galaxy-traced overdensities consistent with bias like dark matter. We conclude that the ELAF may provide a new tool for tracing a significant fraction of the cosmic web of baryons and dark matter. Finally, I will present status of the Super-pressure STABLE Cosmic Web Imager (SSCWI) program, a Brinson Exploration Hub balloon experiment, focused on emission from the Circum-QSO, the Circum-Galactic Medium, and the cosmic web. SSCWI offers the opportunity to image the cosmic web in the local universe for the first time, and compare its properties to those at high redshift.
Tues. Apr 22: Joanna Woo (SFU), in-person (Recording)
The Diverse Lives of Galaxies
It has been long established that galaxies can be divided into those that star-forming spiral discs and those that are spheroids that have stopped forming stars long ago. Despite decades of attempts to fit galaxy evolution into a cookie-cutter model, it is becoming evident that galaxies grow and evolve from one class to the other through numerous evolutionary pathways. From passive evolution to the dramatic influence of black hole activity driving gaseous outflows, to the influence of the vast cosmic web, I will review the different drivers of galaxy evolution in light of the latest observational and theoretical discoveries. In particular I will highlight new research from my group that explores the influence of the cosmic web on the evolution of galaxy structure.
Tues. Apr 15: Cail Daley (CEA Saclay, France), (Recording)
Cosmology with SPT-3G
The 10-meter South Pole Telescope (SPT) is designed to observe the Cosmic Microwave Background (CMB) and astrophysical foregrounds with observing bands at 95, 150, and 220 GHz. The third-generation SPT-3G experiment began its Main 1500 deg² survey in 2019, and the inclusion of SPT-3G’s Summer and Wide fields brings the combined Ext-10k survey area above 10,000 deg² (25% of the sky). A suite of primary anisotropy and lensing analyses using data from the 2019 and 2020 Main observing seasons is almost complete, and the first Bayesian polarization-only results were presented in Ge et al. (2024). Combined constraints from this dataset are comparable to those from the Planck satellite, and the Ext-10k survey will improve constraints by up to a factor of 2 relative to Planck. SPT-3G’s lensing maps will also be used to delens polarization data from the BICEP-Keck experiment in the search for primordial gravitational waves, and cross-correlations between polarization-based lensing maps and external mass tracers will provide insights into the growth of structure robust to foregrounds that can bias temperature-based lensing reconstructions. Finally, SPT-3G has conducted dedicated observations of the Euclid Deep Field South to be publicly released on a similar timescale to Euclid Q1, providing a rich testbed for cross-correlations between deep CMB and galaxy surveys. In this talk I will discuss recent and upcoming cosmology results from SPT-3G that are largely independent of Planck, allowing for consistency tests between the two data sets and potentially revealing evidence of new physics.
Tues. Apr 8: Maya Fishbach (UofT), in-person (Recording)
Gravitational Waves from the Stellar Graveyard
The LIGO-Virgo-KAGRA Collaboration has observed hundreds of gravitational-wave sources to date, including mergers between black holes, neutron stars, and mixed neutron star–black holes. These neutron stars and black holes connect many astrophysical puzzles, including the lives and deaths of stars, star cluster dynamics, cosmic chemical enrichment, and the expansion history of the Universe. I will describe some recent astrophysical lessons from gravitational-wave discoveries.
Tues. Apr 1st: Matt Holman (Harvard/CfA), in-person (Recording)
A Pan-STARRS Search for Distant Planets
I present a search for distant planets in Pan-STARRS1 data. This search has been calibrated by injecting an isotropic control
population of synthetic detections into Pan-STARRS1 source catalogs, providing a high-fidelity approximation to injecting synthetic sources at the image level. The search method is sensitive to a wide range of distances, as well as all rates and directions of motion. The search discovered and recovered 692 solar system objects, including 642 TNOs, 23 of which are dwarf planets. By raw number of detections, this is the third most productive Kuiper Belt survey to date, in spite of the fact that distances closer than 80 au were not explicitly searched. Although the search did not find Planet Nine or any other planetary objects, to date, it shows that the remaining parameter space for Planet Nine is highly concentrated in the galactic plane. A catalog-based approach to characterizing searches will be increasingly important for surveys such as Rubin, Euclid, and Roman, for which injecting synthetic moving sources directly into the images will be even more challenging.
Tues. Mar 25th: Michelle Kunimoto (UBC), in-person (Recording – apologies, missed first few minutes)
Exploring Exoplanet Demographics with Kepler, TESS, and Beyond
Exoplanet surveys have been spectacularly successful in identifying thousands of planets with breathtaking diversity. These discoveries help place the Solar System in context and inform our understanding of how planets form and evolve. Finding large numbers of planets also enables statistical studies of the exoplanet population, through which we can uncover which types of planets are more common than others and find correlations between planet abundance and the properties of stars. Exoplanet demographic studies are key for constraining planet formation and evolution theories. I will highlight contributions to the field of demographics, from large and small planet populations with NASA’s Kepler mission and its implications for the search for other Earths, to the exciting potential of NASA’s TESS mission to significantly expand our understanding of planet populations around more diverse stellar samples than were possible before. Finally, I will identify a set of important open questions that remain to be answered and outline future goals to push the field of demographics to new frontiers.
Winter 2025
Tues. Mar 11th: Christine Wilson (McMaster), in-person (Recording)
A tale of two mergers: molecular gas and star formation in extreme environments
The merger of two gas-rich galaxies can produce some of the highest rates of star formation found in the present-day Universe. Understanding how this burst of star formation is triggered has implications for understanding star formation at higher redshift, where star formation rates of 100 solar masses per year were much more common than they are today. I will present our recent work on measuring molecular gas properties at 100 pc resolution in two nearby mergers, the Antennae and NGC 3256. We find that molecular clouds in these galaxies have turbulent line widths and column densities that are significantly higher than those found in normal spiral galaxies. These different cloud properties likely play a key role in enabling rapid star formation in these galaxies.
Tues. Feb 25th: Zhibo Hau, in-person (Recording)
Development of Data Reduction Pipeline and Calibrators for High-Precision RV Measurements with 216-HRS
Radial velocity technique for exoplanet detection has made great achievements. It discovered the first exoplanets beyond the solar system, which was awarded the Nobel Prize in 2019, and has confirmed 1,100 exoplanets by now. The recent 30 years witnessed the sensitivity of RV measurement progress from several tens of m/s (ELODIE) to 0.4 m/s (ESPRESSO), with the aid of improvements in spectrograph optics, stability, and the application of new technologies, such as new wavelength calibrators and data reduction techniques. In recent years, an upgrade project for the high-resolution spectrograph (216-HRS) at the Chinese Xinglong 2.16-m Telescope has been implemented, aiming to enable rocky planet detection around M-dwarfs – whose typical RV signal is 1 m/s – by transforming it from an iodine-technique-based spectrograph to a HARPS-like fiber-fed spectrograph. During my doctoral research, I engaged in this project, focusing on addressing the challenges in calibration and data reduction. I developed a data reduction pipeline software for 216-HRS. This software processes raw images into high-quality spectra and enables calibration with both traditional calibrators, the Thorium-Argon lamp, and newly developed advanced calibrators, the astro-comb and the Fabry-Perot etalon (FPE). The pipeline achieved a photon-noise-limited 0.1 m/s calibration precision with the astro-comb and sub-1-m/s calibration precision with the temperature-stabilized solid FPE. It enabled 216-HRS to achieve the calibration precision necessary for detecting rocky exoplanets.
Tues. Feb 12th: Paul Bennet (STScI), in-person (Recording)
Orbital insights into distant Local Group dwarfs
In general, our current understanding of classical dwarf galaxies is that they are star-forming when in the field and quench via tidal forces and/or ram pressure stripping as they approach massive hosts. However, recent results from the Local Volume, such as the SAGA survey, have shown that our current understanding might be over-quenching dwarf galaxies. Many Milky Way (MW) analog galaxies having more star-forming low-mass satellites than expected. We have also observed quenched dwarf galaxies in the wider LG, distant from either M31 or the MW, contrary to what simulations predict. These quenched dwarfs are often explained as backsplash galaxies that have had a previous encounter with a massive host; but have now moved outside the virial radius. I will present our ongoing efforts to obtain new proper motions with HST for a sample of distant dwarf galaxies in the LG, significantly expanding both the number of systems for which we have full 6D position-velocity information and crucially looking at more distant dwarfs than previous samples. I will also discuss how our work shows that the star formation properties might not be so cleanly divided with quenched dwarfs and star forming dwarfs having separate interaction histories.
Tues. January 7th: Anna Ho (Cornell), in-person (Recording)
Finding Relativistic Stellar Explosions as Fast Optical Transients
For the last half-century, relativistic outflows accompanying the final collapse of massive stars have predominantly been detected via high-energy emission, as long-duration gamma-ray bursts (GRBs). Yet, it has long been hypothesized that GRBs are the tip of the iceberg of relativistic stellar explosions, because the conditions required to produce and detect a GRB are contrived. I will present results from a search for relativistic stellar explosions using optical time-domain surveys. The emerging zoo includes afterglows at cosmological distances with no detected GRB, supernovae with luminous X-ray and radio emission, and a mysterious class of “fast blue optical transients” with minute-timescale optical flares at supernova-like luminosities. An understanding of the origin of these events and their relation to GRBs will be enabled by upcoming time-domain surveys in other bands, including X-ray, UV, and submillimeter.
Fall 2024
Tues. December 10th: Laurence Perreault Levasseur (Université de Montréal, MILA, & Flatiron Institute), in-person Recording
Tues. October 29th: Mike Brown (Caltech), remote Recording
Astronomers have been predicting and searching for planets beyond Neptune for almost 180 years. In all previous cases the predictions were based on bad data, bad physics, or both, and the predictions turned out to be wrong. In 2016, we joined this inglorious group and declared that orbital alignments of the most distant objects in the solar system demand the presence of a distant giant planet on an eccentric and inclined orbit. I’ll describe the mounting evidence for this planet, discuss the counter-proposals, and talk about the ongoing search for what would be the fifth largest planet of our solar system.
Tues. October 22nd: Matthew Lehner (ASIAA), in person Recording
The Transneptunian Automated Occultation Survey (TAOS II)
The TAOS II survey is designed to measure the size distribution of small Trans-Neptunian Objects (TNOs), critical for understanding the formation and evolution of our Solar System. These objects are too faint for direct detection, so TAOS II will search for rare and brief occultations of stars by TNOs, requiring high-cadence observations across three telescopes at San Pedro Martir Observatory in Mexico. With cutting-edge CMOS imagers, TAOS II will collect an unprecedented dataset, offering rich opportunities for both core occultation science and additional research.TAOS II is a collaboration between ASIAA (Taiwan), NRC (Canada), IA-UNAM (Mexico), and the CfA (USA). Members of the four collaborating institutes will have first access to this dataset. As such, members from these institutes are strongly urged to contribute to the scientific output of this survey, preferably in collaboration with members of other collaborating institutes.
In this presentation, I will outline the survey’s key science objectives, the unique capabilities of the TAOS II facility, and collaborative opportunities within the international team. I will also preview the upcoming TAOS II science workshop next spring.
Tues. September 24: Danny Horta (Flatiron), in person Recording
A glimpse into the Milky Way’s distant past: unravelling the Galaxy’s early assembly history with large stellar surveys
Unravelling galaxy formation theory requires understanding galaxies both at high and low redshifts. A possible way to connect both realms is by studying the oldest stars in the Milky Way (i.e., the proto-Galaxy). Our ability to resolve individually millions of stars in the Galaxy provides us with the opportunity to decipher the intricate processes of galaxy formation in a detail that is unmatched by any other galaxy in the Cosmos. Therefore, the time is ripe to study the oldest parts of the Milky Way, and from them unravel its early mass assembly history. Such results, in addition to placing strong constraints on how our Galaxy formed, are also complementary to the new exciting results of the high-redshift Universe delivered by the JWST telescope. In this talk, I will present new findings aiming to piece together the earliest stages of formation of the Milky Way by examining the chemistry, kinematics, and orbits of the oldest stars in the Galaxy. I will also show fresh results concerning the structure and mass of the Milky Way’s proto-galactic fragments. I will then place these observational findings in the wider context of the many possible assembly histories by comparing with expectations from cosmological simulations. The findings I will present help answer (but raise more) fundamental questions on the genesis of our Galaxy.
Tues. September 17: Rebecca Jensen-Clem (UCSC), virtual Recording
Exoplanet Imaging with Extremely Large Telescopes
The last three decades have been marked by the discovery of over 5000 exoplanets orbiting nearby stars. Unraveling these planets’ compositions, climates, and formation histories requires spectra of their thermal emission and reflected starlight; direct imaging is the only path forward for obtaining high signal-to-noise, high-resolution spectra of diverse exoplanet atmospheres. Today, only a handful of massive super-Jupiters have been imaged, while faint Earth-sized planets remain hidden in the glare of their host stars. My work combines adaptive optics (AO) technology development with high contrast observations to advance the state-of-the-art in exoplanet imaging. In this talk, I will discuss (1) the limits of today’s high contrast imaging systems and the AO technology development efforts at UC Santa Cruz and W. M. Keck Observatory that aim to address these limitations, including primary mirror segment phasing, multi-stage wavefront sensing, and astrophotonics; (2) the new high contrast science enabled by these technology development activities with today’s 10-meter-class telescopes and the next generation of 30-meter-class telescopes.
Tues. September 10: Jenny Greene (Princeton), virtual Recording
The Nature of “Little Red Dots”
One of the most surprising results from JWST has been the discovery of a large population of compact red sources at z>4, with very red rest-frame optical colors, blue UV slopes, and broad Balmer lines. The compact sizes and luminous broad lines strongly suggest these objects are powered by accreting supermassive black holes, but their lack of evidence for X-ray emission or hot dust in the mid-infrared calls that conclusion into question. Regardless, their high number densities (~5% of the galaxy population) makes them an important new contribution to the high-redshift galaxy zoo. I will discuss our ongoing efforts to understand the nature of this population, and what they may teach us about the growth of black holes and galaxies.