DAO Astronomy Colloquium Schedule
In person talks will take place in the LCR and will be streamed live online via Zoom.
Tuesdays at 11am unless otherwise indicated with (***)
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)
Tues Dec 6th, 11am, Zoom: Alex Tetarenko (Texas AM)
Tues Dec 13th, 11am, Zoom: Mike Chen (Queens University)