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.
January 22, 2020
- "Overview and Status of the Giant Magellan Telescope Project"
- Staff Astronomer
- Carnegie Observatories
Optical-IR telescopes have driven astronomical discovery for over 400 years. The next generation of "extremely large" ground-based telescopes (ELTs) will provide a leap in sensitivity and resolution that will revolutionize exoplanet research and expand the frontiers in nearly every area of astrophysics and cosmology. The Giant Magellan Telescope (GMT) is one of the two US ELTs currently underway. It is a 25m-diameter telescope being built in northern Chile by an international collaboration of universities and research institutions. The GMT project is advancing rapidly, with final design work, mirror fabrication, prototyping, and construction of site infrastructure all currently progressing in parallel. I will give a brief overview of the design, capabilities, and the science accessible with the GMT, and an update on the project status. Finally, I will discuss the community-wide efforts to launch the US-ELT Program, which is a partnership between the NSF’s Optical-IR Astronomical Research Lab, the Thirty Meter Telescope (TMT) project, and GMT that would providing the entire US astronomy community with access to both GMT and TMT through NSF participation in both projects.
January 29, 2020
- "Rethinking metallicity: the quest to measure the chemistry of distant galaxies"
- Postdoctoral Fellow
- Carnegie Observatories
Large near-infrared spectroscopic surveys have confirmed that star-forming galaxies at cosmic noon (z~2-3) exhibit nebular spectra that are distinct from their local counterparts. These differences reflect important changes in the characteristic physical conditions and chemical enrichment patterns of galaxies at early times, correlated with differences in their star formation histories relative to most present-day galaxies: at z~2, almost all galaxies have nearly constant or rising star formation histories, but by z~0, galaxies overall have lower specific star formation rates and many have largely finished forming stars. Using spectra from the Keck Baryonic Structure Survey (KBSS) and photoionization models designed to reconcile the joint rest-UV-optical spectra of high-z star-forming galaxies, I have shown that the majority of z~2-3 galaxies have moderate oxygen enrichment but sub-solar iron enrichment as a result of their rapid assembly histories. I will argue that this marked alpha-enhancement means that it is imperative to consider abundance patterns rather than a single "metallicity" when describing galaxies' chemical enrichment. I will also report new measurements of the correlation between galaxy stellar mass and multiple chemical tracers (including O, N, and Fe) at z~2-3 using my photoionization model method and discuss extant challenges to comparing metallicity scaling relations with predictions from cosmological simulations. These comparisons are critical for understanding the way in which energetic feedback acts to regulate star formation in galaxies throughout cosmic time, which remains an open question in modern astrophysics and will be one of the key science drivers of upcoming facilities such as the James Webb Space Telescope and the ELTs.
February 5, 2020
- Hubble Fellow
- Carnegie Observatories
February 12, 2020
- "eROSITA: Generating the next generation X-ray-all sky map and opening the window into the X-ray-Transient Sky"
- Postdoctoral Researcher
- Leibniz-Institute for Astrophysics Potsdam (AIP); former CASS member
The X-ray instrument eROSITA (extended Roentgen Survey with an Imaging Telescope Array) aboard the Russian spacecraft Spektr-RG was successfully launched on July, 13, 2019 into an L2 orbit. During its four-year primary mission, eROSITA will conduct eight deep 0.2-10 keV all-sky surveys, the first soft all-sky X-ray survey since the ROSAT and the first imaging 2-10 keV all-sky survey ever. eROSITA is expected to detect as many new sources in its first year as have been cataloged in 50 years of X-ray astronomy. The regular, multi-year monitoring will also produce the most comprehensive database of X-ray variability ever.
In my talk I will introduce the instrument eROSITA, the mission Spektr-RG, some first results, and my scientific interest in eROSITA: AGN variability. Each of the single eight all-sky scans will contain roughly one million AGN. In these data, we will search for a) AGN ignition/shut-down (dramatic flux changes between surveys) and b) AGN cloud obscuration events (change in the line-of-sight X-ray absorption). Due to the amount of expected events and the clean selection of sources, we will be able to compute the probabilities that such changes happen. This will allow us to obtain observational constraints on the AGN duty cycle and the distribution of matter around supermassive black holes. I will also show some pictures of my trip to Baikonur, the Russian Cosmodrome, during the eROSITA launch activities.
February 19, 2020
- Professor of Physics & Astronomy
- UC Irvine
February 26, 2020
- Professor, Department of Physics and Astronomy
- UC Riverside
March 4, 2020
- NSF Postdoctoral Fellow
- UC Berkeley
March 18, 2020
- "The Duration of Star Formation in Galactic Giant Molecular Clouds"
- Associate Professor, Department of Physics & Astronomy
- Cal Poly Pomona
Stars and planets are born in vast interstellar clouds of cold gas and dust called giant molecular clouds (GMCs). I have led a collaboration of researchers and undergraduate students in the development a novel infrared (1 - 8 µm) spectral energy distribution modeling methodology to place X-ray-identified, intermediate-mass (2 - 5 Msun), pre-main sequence stars (IMPS) on the Hertzsprung-Russell diagram. Compared to the more numerous and widely-studied low-mass stars, the temperature and luminosity of IMPS changes dramatically over the first few million years of evolution, hence IMPS serve as sensitive chronometers for measuring the ages of the youngest massive stellar populations in the Galaxy. We apply our methodology to constrain the duration of star formation in a sample of ~20 massive star-forming regions in our Milky Way Galaxy that suffer significant differential reddening from obscuring foreground dust. Star formation commenced at different times among our sample GMCs, ranging from <1 Myr to ~9 Myr ago. We find that the nebular IR luminosity surface density decays sharply with time after the onset of star formation. Dust has been evacuated from giant H II regions produced by massive stellar clusters older than ~3 Myr, rendering them IR-faint. This short timescale indicates that radiation pressure and winds from massive, OB stars generally disperse GMCs before the onset of supernovae. Spatially-resolved IR indicators of obscured star formation rates, commonly used for nearby external galaxies, may need to be recalibrated to account for the brief lifetimes of IR-bright, dusty H II regions.
April 1, 2020
- 51 Pegasi b Fellow
April 15, 2020
- Deputy Director
- UC Observatories
May 27, 2020
- JWST Observatory Project Scientist
- NASA Goddard Space Flight Center