DAO Astronomy Colloquium


DAO Astronomy Colloquium Schedule

Online via Zoom, Victoria

Tuesdays at 11am unless otherwise indicated with (***)

Archive of previous seminar schedules (2010-)
Link to remote connection information

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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)

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.