The CASS Astrophysics Seminar features world-class astrophysicists from around the world speaking on current topics of research. Presentations are aimed at the graduate and post-graduate level, but are open to the general public. CASS seminars take place on Wednesdays from 3:00 - 4:00 p.m. in 383 SERF (Marlar Seminar Room), unless otherwise noted. You can watch a live stream of the talk or prior talks at the CASS Seminar YouTube Channel. The seminar organizer is Prof. Karin Sandstrom.
October 2, 2019
- "The darkest galaxies"
- Assistant Professor
- Rochester Institute of Technology
Recent years have witnessed the discovery of the faintest dwarf galaxies, which are some of the most dark-matter dominated objects in the universe. Understanding the darkest dwarf galaxies may ultimately help us unravel the nature of dark matter. I will begin by reviewing our earlier work where we developed a new dynamical method to hunt for the darkest galaxies from analysis of their gravitational imprints on the outer gas disks of spiral galaxies. I will discuss our earlier prediction for a new Milky Way satellite based on the analysis of perturbations on the outer gas disk of our Galaxy. I will then discuss new Gaia DR-2 data of the recently discovered Antlia 2 dwarf galaxy that is at a radial location and with properties similar to our prediction, and may represent the first successful application of Galactoseismology. I will also review the prospects for understanding the dynamics of the Milky Way disk with Gaia data, which now gives unprecedented phase space information on the stellar disk of our Galaxy. I will end by presenting preliminary work contrasting the effects of different dark matter models on the dynamical evolution of the density profile of the Antlia 2 dwarf galaxy. The Antlia 2 dwarf galaxy is the lowest surface brightness galaxy known to date, and represents an ideal laboratory for studying dark matter.
October 9, 2019
- "The Galactic 511 keV Positron Puzzle"
- Postdoctoral Scholar
For half a century, the strongest, persistent, diffuse, gamma-ray line signal from the annihilation of electrons with positrons is puzzling theorists and observers. Unlike at any other wavelength, this 511 keV emission is dominated by a bright bulge emission, in addition to a very low surface-brightness disk. The two main questions of this ‘positron puzzle’ are summarised into “where do the positrons come from?”, and “why does the emission look like that?”. While the problem is not finding a single source to sustain the annihilation rate - it is rather that there are too many possibilities to explain the observations. Most astrophysical phenomena, such as massive stars, supernovae, compact objects, cosmic rays or dark matter can - in principle - produce positrons; however direct observations are difficult. I will present a summary of the ‘positron puzzle’, recent updates on the 511 keV emission morphology and its kinematics with data from INTEGRAL/SPI, as well as an unpopular attempt to balance the positron budget by using Chatton’s antirazor. Finally, I will provide an outlook on what will be possible with future compact Compton telescopes such as the Compton Spectrometer and Imager, COSI.
October 16, 2019
- Keck Institute for Space Science Postdoctoral Fellow
October 23, 2019
- Professor, Canadian Institute for Theoretical Astrophysics (CITA)
- University of Toronto
October 30, 2019
- Professor, Lunar & Planetary Lab
- University of Arizona
November 6, 2019
- CASS Postdoctoral Scholar, UC President's Postdoctoral Fellow
November 13, 2019
- "Decoding Galaxy Formation Physics with the UniverseMachine"
- Assistant Professor, Department of Astronomy
- University of Arizona
I discuss new methods that allow computers to recover the underlying physics of galaxy formation using only galaxy observations and dark matter simulations, and show how these methods have already changed our understanding of galaxy formation physics (including why galaxies stop forming stars). Basic extensions to the same techniques allow constraining internal galaxy processes, including coevolution between galaxies and supermassive black holes as well as time delays for supernova / GRB progenitors. Finally, I discuss how these methods will benefit from the enormous amount of upcoming data in widefield (HETDEX, LSST, Euclid, WFIRST) and targeted (JWST, GMT) observations, as well as ways they can benefit observers, including making predictions for future telescopes (especially JWST) and testing which of many possible targeted observations would best constrain galaxy formation physics.
November 20, 2019
- Postdoctoral Scholar, CASS
December 4, 2019
- Professor, Department of Physics and Astronomy
- UC Riverside
December 11, 2019
- Hubble Fellow
- Carnegie Observatories
January 22, 2020
- Staff Astronomer
- Carnegie Observatories
February 19, 2020
- Professor of Physics & Astronomy
- UC Irvine