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Astrophysics Seminars


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 4:00 - 5:00 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 organizers are Prof. Shelley Wright and Prof. George Fuller.

Upcoming Seminars

Fall 2017

October 18, 2017

 "Outflows in active galactic nuclei"

Sibasish Laha
Postdoctoral Scholar

 The last couple of decades have seen the most crucial developments in the understanding of AGN winds. This can be attributed mostly to the advent of great observatories like ALMA (Molecular outflows), Hubble space Telescope (UV outflows), XMM-Newton and Chandra (X-ray outflows). Coupled with advancement in theories, our understanding about AGN outflows in different wavelength bands (Radio, Infra-red, Optical, UV and X-rays) has never been better, yet there are many outstanding questions which we still need to answer. We present here the results from a comprehensive study of the warm absorbers (WA) in X-ray in a flux limited complete sample of Seyfert galaxies (WAX-I, Laha et. al. 2014, MNRAS 441, 2613), using high resolution XMM-Newton data. We found that the WA clouds are present in around 65% of the sources. We also found a gap in the ionization parameter distribution of the WA, pointing to thermal instability. We have found evidences of WA being radiatively driven and they originate from the dusty torus (WAX-II, Laha et al. 2016, MNRAS 457, 3896L). The dust opacity can also play a leading role in driving these clouds. These WA clouds can sometimes give “effective feedback” to the host galaxies. In another extensive sample study of AGN exhibiting molecular outflows (to be submitted), we find that the AGN plays the most important role in driving these large kpc scale outflows. However, we are still uncertain how the AGN interacts with these large scale molecular clouds.

October 25, 2017

 "What matter(s) around galaxies? Shining a bright light on the cold phase of the
Circum Galactic Medium"

Sebastiano Cantalupo
Assistant Professor
Institute for Astronomy, ETH Zurich

 I will present the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external "sources of illumination’. By looking in emission rather than in absorption, this program provides new and unique information on the morphology and physical properties of the cold phase of the Circum Galactic Medium (CGM) on both large and small scales. In particular, I will show results from ultra-deep narrow-band imaging and recent integral-field-spectroscopy as a part of the MUSE Guaranteed Time of Observation program that revealed numerous giant Lyman-alpha emitting filaments extending up to several hundred kpc around quasars and bright galaxies. I will discuss how the unexpectedly high luminosities of these systems, together with the constraints from Helium and metal extended emission, represent a challenge for our current understanding of cosmological structure formation. In particular, I will show that current observations suggest that a large amount of “cold" and dense gaseous “clumps" should be present around high-redshift galaxies and I will present our first attempts to understand the origin and nature of these structures in the Early Universe. At the same time, current galaxy formation models lack an efficient mechanism to prevent too much cooling of the CGM onto galaxies at later epochs and rely on very strong “ejective" feedback. In the second part of the talk, I will show how the interaction between high-energy radiation from star-forming galaxies and the CGM - still ignored by almost all galaxy formation models - provides a natural way to prevent excessive CGM cooling onto galaxies (“preventive” feedback). Finally, I will mention recent COS observations that provide support for the importance of this “preventive” feedback mechanism and, at the same time, can give vital constraints on the SED of star-forming galaxies in the FUV range.

November 1, 2017

 "The Development of the Next Generation Instrumentation for the Compton
Spectrometer and Imager"

Jarred Roberts
Postdoctoral Scholar

 The Compton Spectrometer and Imager (COSI) is a balloon-borne, soft-gamma ray imager, spectrometer, and polarimeter with sensitivity from 0.2 to 5 MeV. Utilizing a compact Compton telescope design with twelve cross-strip, high-purity germanium detectors, COSI has three main science goals: to study the 511 keV positron annihilation line from the Galactic plane, to image diffuse emission from stellar nuclear lines, and to perform polarization studies of gamma-ray bursts and other extreme astrophysical environments. The COSI experiment is currently undergoing a significant instrumentation development that aims to improve the energy and angular resolution of the instrument. This talk will focus on the current status of these developments and the scientific motivation for making these improvements to the instrument.

November 8, 2017

Cameron Hummels
NSF Postdoc Fellow

November 15, 2017

 "Clouds in the Galactic Sky - The Gaseous Halos of Galaxies from the synergy of Observation and Theory"

Cameron Liang
Graduate Student, Department of Astronomy and Astrophysics
University of Chicago

 Undoubtedly, the Earth's atmosphere is an integral part of its ecosystem. Everyday weather and long-term climate of the atmosphere are directly linked to activities on the surface of the Earth and vice versa. Gaseous halos, known as the circumgalactic medium (CGM), are the equivalent atmosphere of galaxies. The galactic climate arises from infalling gas from intergalactic space, enriched materials launched from the interstellar medium and more. The CGM is one of the largest gas reservoirs with complex baryonic cycles. It is paramount to improve our understanding of the CGM to achieve a complete picture of galaxy formation and evolution.

In this talk, I will first focus on the observational efforts to place empirical constraints on the spatial extent and the metallicity of the CGM. I will then present some theoretical work on the baryonic cycles in cosmological zoom-in simulations and show that the CGM provides orthogonal constraints to star formation and feedback processes. Finally, I will present a new high-resolution (< 1pc) simulation study to model the CGM more systematically with radiative cooling, thermal conduction, and magnetic fields.

November 29, 2017

 "Cosmology Results from the Dark Energy Survey Year 1"

Elisabeth Krause
Research Scientist

 This talk presents cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements.

I will describe the validation of measurements and modeling from catalogs to cosmology, and highlight cosmology constraints from the combination of DES Y1 with external data sets.

Based on DES Collaboration 2017 (1708.01530) and supporting papers.

December 6, 2017

 "The Breakthrough Listen Search for Advanced Life Beyond Earth”

Andrew Siemion
Director, Berkeley SETI Research Center
UC Berkeley

 The Breakthrough Listen Initiative is an ambitious effort to conduct the most comprehensive and sensitive search for advanced extraterrestrial life in humanity’s history. Breakthrough Listen has secured approximately 20% of the time on two of the largest radio telescopes in the world, the 64m Parkes Telescope in NSW, Australia and the 100m Green Bank Telescope at Green Bank Observatory in West Virginia, along with 36 nights per year on the 2.4m Automated Planet Finder at Lick Observatory. Breakthrough Listen has also entered into an agreement with the National Astronomical Observatory of China to collaborate on the development of search techniques, software and observing procedures for the 500m FAST Telescope, and the Jodrell Bank Observatory / University of Manchester to work together in a similar fashion toward developing SETI capabilities on the 76m Lovell Telescope and the MERLIN network.

Breakthrough Listen observations at the APF employ the Levy Spectrometer to conduct ``spectroscopic optical SETI’’ observations, searching for artificially narrow spectral lines that are known only to arise from technological sources (lasers). At the GBT and Parkes, Breakthrough Listen is deploying state-of-the-art digital backends capable of searching for a wide variety of signals indicative of a technological source, across many GHz of instantaneous bandwidth. As of this writing, Breakthrough Listen has deployed a 6 GHz system at the Green Bank Telescope and a 5 GHz system at the Parkes Telescope.

The current Breakthrough Listen target list includes a spectral-type complete sample of nearby stars, 100 nearby galaxies spread over all morphological types, a complete survey of the galactic plane and exotic objects and targets of opportunity (e.g. KIC 8462852, FRB121102). The Breakthrough Listen team is currently exploring opportunities to engage in commensal SETI programs with the SKA and its precursors. These potential extensions to the Breakthrough Listen program would allow significant expansion of the Breakthrough Listen target list and would lay the groundwork for extremely high sensitivity observations with the full SKA. These latter observations would be the first SETI ever conducted that would be sensitive to Earth-level leakage radiation from nearby stars.

Here I will review the Breakthrough Listen program, current observational capabilities and latest results.

Winter 2018

January 10, 2018

Brandon Hensley
Postdoctoral Fellow

January 17, 2018

Jérémy Chastenet
Postdoctoral Scholar

January 24, 2018

Victor Robles
Postdoctoral Researcher
UC Irvine

February 7, 2018

NOTE: Joint Astro-Plasma Physics Seminar

Ellen Zweibel
W. L. Kraushaar Professor of Astronomy & Physics, Department of Astronomy
University of Wisconsin-Madison

February 28, 2018

John Tomsick
Researcher, Space Sciences Lab
UC Berkeley

March 7, 2018

Emily Pringle
Scripps Postdoctoral Fellow

Spring 2018

April 25, 2018

Jorge Pineda
Research Scientist

May 9, 2018

Jessica Werk
Assistant Professor
University of Washington

May 16, 2018

Ruth Murray-Clay
UC Santa Cruz