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Astrophysics Seminars

Contents

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.


Upcoming Seminars

Winter 2020


February 26, 2020

 "Black Hole Feedback in Dwarf Galaxies"

Gabriela Canalizo
Professor, Department of Physics and Astronomy
UC Riverside

 Black holes are believed to populate the centers of all galaxies with mass comparable to the Milky Way and above. For massive galaxies, the interaction of black holes and their accretion disks with the surrounding gas leads to the formation of powerful gas outflows that heat up and may eventually escape the galaxy. However, in low mass dwarfs, the most common type of galaxies in the Universe, the incidence of massive black holes is largely unknown and their effects on star formation histories are currently ignored. In this talk, I will present the discovery and measurement of extended gas outflows powered by black holes dwarf galaxies using spatially resolved Keck/LRIS spectroscopy. The measured outflow velocities are enough to escape the galaxy and their surrounding dark matter halo, leaving behind a gas-depleted and poorly star-forming galaxy. We find some evidence for star formation suppression, mostly by the active galactic nuclei. Galaxy formation models must therefore be able to account not only for the formation and growth of black holes in the centers of dwarf galaxies but should also be revised to include black holes as important --and perhaps dominant-- sources of feedback in low mass galaxies.



March 4, 2020

 "Cosmology with Massive Neutrinos"

Jia Liu
NSF Postdoctoral Fellow
UC Berkeley

 Ghostly neutrino particles continue to bring surprises to fundamental physics, from their existence to the phenomenon of neutrino oscillation which implies that their masses are nonzero. Their exact masses, among the most curious unknowns beyond the Standard Model of particle physics, can soon be probed by the joint analysis of upcoming cosmological surveys including LSST, Euclid, WFIRST, Simons Observatory, and CMB-S4. In this talk, I will first discuss ongoing work studying the effects of massive neutrinos. I will then turn the focus to my major efforts of modeling the challenging nonlinear regime of cosmic structures (<10 Mpc) where neutrino effects are the strongest. Finally, I will draw a roadmap to pin down the neutrino mass over the next decade.



March 11, 2020

JD Smith
Professor of Astronomy
University of Toledo



March 18, 2020

 "The Duration of Star Formation in Galactic Giant Molecular Clouds"

Matthew Povich
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.


Spring 2020


April 1, 2020

 "Finding an Alien Biosphere with Computational Chemistry"

Clara Sousa-Silva
51 Pegasi b Fellow
MIT

 At the edge of our present scientific frontier lies the question: “Can we identify the signs of life on an exoplanet?”. Establishing whether a planet is habitable, or inhabited, relies both on the observation of an exoplanet atmosphere and, crucially, its subsequent interpretation. This interpretation requires knowledge of the spectral behavior of every significant atmospheric molecule. However, though thousands of molecular candidates can contribute towards the spectrum of an atmosphere, data exist for only a few hundred gases. Among these, only a fraction have complete spectra (e.g. ammonia, water). This deep incompleteness in the knowledge of molecular spectra presents a pressing vulnerability in the atmospheric study of planets; there exists a strong possibility of mis-assignment, false positives, and false negatives in the detection of molecules. The work presented here combines structural organic chemistry and quantum mechanics to obtain the necessary tools for the interpretation of astrophysical spectra and, ultimately, the detection of life on an exoplanet. Whether alien life will produce familiar gases (e.g., oxygen) or exotic biosignatures (e.g., phosphine), painting a confident picture of a potential biosphere will require a holistic interpretation of an atmosphere and its molecules. In this talk Clara will describe the ongoing efforts to decipher exoplanet atmospheres through the identification of volatile molecules, in particular those that might be produced by non-Earth-like life on exoplanets.



April 8, 2020

Kathryn Kreckel
Emmy Noether Research Group Leader
Zentrum für Astronomie der Universität Heidelberg



April 15, 2020

Matthew Shetrone
Deputy Director
UC Observatories



April 22, 2020

Seyda Ipek
UC President's Postdoctoral Fellow
UC Irvine



April 29, 2020

Gina Panopoulou
NASA Hubble Fellow
Caltech



May 6, 2020

Tzu-Ching Chang
Researcher
NASA-JPL



May 13, 2020

Joshua Pepper
Associate Professor, Department of Physics
Lehigh University



May 20, 2020

Gerardo Dominguez
Associate Professor of Physics
CSU San Marcos



May 27, 2020

Michael McElwain
JWST Observatory Project Scientist
NASA Goddard Space Flight Center