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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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***, ZoomTakuma 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***, ZoomEmily 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.

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)

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)

Cosmicflows-4: Tip of the Red Giant Branch Distances: The tip of the red giant branch (TRGB) is becoming the preferred technique to determine accurate distances to galaxies within the local Universe. The method involves using the brightest red giant branch stars as standard candles, and has now been applied to nearly 500 galaxies within 20 Mpc. Accurate distances are essential for transforming observed properties of galaxies into their physical counterparts (luminosity, physical size, etc.). In addition to their inherent benefits, distances allow us to disentangle the two components of a galaxy’s observed velocity, the component due to the Hubble Flow, and its peculiar velocity. With the latter, we map the patterns of large-scale galaxy flows, and provide insight into the formation and evolution of large-scale structure. In this talk, I will present an update on the TRGB component of the Cosmicflows-4 program, and showcase several recent results from this work, including a discussion on the implications for the value of the Hubble Constant.

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

Tues April 27th, 11am, ZoomOliver Müller (U. of Strasbourg)

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

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

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

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

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