Jump to: navigation, search

Astrophysics Seminars From 2020 - 2021


Fall 2020

September 30, 2020

NOTE: No seminar today

October 7, 2020

 CASS-SDSU Seminar welcome event led by George Fuller/Eric Sandquist

Zoom link

 Zoom password: cass-sdsu

October 14, 2020

 "WIMP Dark Matter In An Unusual Cosmological History"

Seyda Ipek
UC President's Postdoctoral Fellow
UC Irvine

 Or iPhone one-tap :
US: +16699006833,,98208404473# or +12133388477,,98208404473#
Or Telephone:
Dial(for higher quality, dial a number based on your current location):
US: +1 669 900 6833 or +1 213 338 8477 or +1 669 219 2599 or 888 475 4499 (Toll Free) or 833 548 0276 (Toll Free) or 833 548 0282 (Toll Free) or 877 853 5257 (Toll Free)
Webinar ID: 982 0840 4473
International numbers available:

ABSTRACT: WIMP miracle has been an important paradigm in the search for dark matter. However the WIMP parameter space is under great tension from direct detection experiments. I will give you a WIMP scenario with an alternative cosmological history of our universe where the quarks confined into mesons at an earlier stage compared to the standard cosmology with the Standard Model. This alternate scenario will open up WIMP parameter space that is not excluded by dark matter experiments.

October 21, 2020

 "A Glimpse Below the Lyman Limit: New observational advances on the escape of ionizing photons from local galaxies"

John Chisholm
UT Austin

 Or iPhone one-tap :
US: +16699006833,,98688518404# or +12133388477,,98688518404#
Or Telephone:
Dial(for higher quality, dial a number based on your current location):
US: +1 669 900 6833 or +1 213 338 8477 or +1 669 219 2599 or 833 548 0276 (Toll Free) or 833 548 0282 (Toll Free) or 877 853 5257 (Toll Free) or 888 475 4499 (Toll Free)
Webinar ID: 986 8851 8404
International numbers available:

ABSTRACT: The neutral gas between galaxies was rapidly reionized at redshifts between 6-10. The origin of these ionizing photons remains elusive, but fundamentally shapes the subsequent evolution of the galaxies and the formation of large-scale structure in the universe. The key to unraveling the epoch of reionization is an understanding of both the sources emit ionizing photons (stars vs. active galactic nuclei) and how these ionizing photons escape galaxies. I will present an overview of the recent observational advances that have led to the discovery of local star-forming galaxies that emit ionizing photons, including a recent large Hubble Space Telescope survey that has more than doubled the known number of emitters of ionizing photons. A statistical sample allows for the first detailed look into what types of star-forming galaxies emit ionizing photons and how those ionizing photons can escape star-forming galaxies. I will focus on new probes from the rest-frame ultraviolet that promise to diagnose the porosity of the neutral medium within galaxies at high-redshift. These local surveys set the stage for upcoming telescopes to determine the impact of star-forming galaxies on Cosmic Reionization.

October 28, 2020

 "Inference can constrain a model of neutrino flavor transformation in core-collapse supernovae”

Eve Armstrong
Assistant Professor, Department of Physics
New York Institute of Technology

 Or iPhone one-tap :
US: +12133388477,,95800291521# or +16692192599,,95800291521#

Or Telephone:
Dial(for higher quality, dial a number based on your current location):
US: +1 213 338 8477 or +1 669 219 2599 or +1 669 900 6833 or 888 475 4499 (Toll Free) or 833 548 0276 (Toll Free) or 833 548 0282 (Toll Free) or 877 853 5257 (Toll Free)

Webinar ID: 958 0029 1521

International numbers available:

ABSTRACT: The multi-messenger astrophysics of compact objects presents a vast range of environments where neutrino flavor transformation may occur and may be important for nucleosynthesis, dynamics, and a detected neutrino signal. Development of efficient techniques for surveying flavor evolution solution spaces in these environments, which augment existing computational tools, could leverage progress in this field. To this end, we continue our exploration of statistical data assimilation (SDA) to identify solutions to a small-scale model of neutrino flavor transformation. SDA is a machine learning (ML) formula wherein a dynamical model is assumed to generate any measured quantities. Specifically, we use an optimization formulation of SDA wherein a cost function is extremized via the variational method. Regions of state space in which the extremization identifies the global minimum of the cost function will correspond to parameter regimes in which a model solution can exist. Our study seeks to infer the flavor transformation histories of two mono-energetic neutrino beams coherently interacting with each other and with a matter background. We require that the solution be consistent with measured neutrino flavor fluxes at the point of detection, and with constraints placed upon the flavor content at various locations along their trajectories, including the point of emission and the locations of the Mikheyev-Smirnov-Wolfenstein (MSW) resonances. We show how the procedure efficiently identifies solution regimes and rules out regimes where solutions are infeasible. Overall, results intimate the promise of this “variational annealing” methodology to efficiently probe an array of fundamental questions that traditional numerical simulation codes render difficult to access.

November 4, 2020

NOTE: No seminar today

November 11, 2020

NOTE: No seminar today: Veteran's Day Holiday

November 18, 2020

 "Solar System Archaelogy: Multidisciplinary Approaches to Understanding Planetary System Formation"

Gerardo Dominguez
Associate Professor, Physics
CSU San Marcos

 Or iPhone one-tap :
US: +12133388477,,91549171608# or +16692192599,,91549171608#

Or Telephone: Dial(for higher quality, dial a number based on your current location):
US: +1 213 338 8477 or +1 669 219 2599 or +1 669 900 6833

Webinar ID: 915 4917 1608
International numbers available:

ABSTRACT: Astronomical observations by the Kepler space telescope have confirmed, to date, the existence of over 3,000 planetary systems in our Galactic neighborhood. The distributions of planet size, compositions, and orbital parameters derived from these observations pose a fundamental challenge for models of planetary system formation which currently do not provide an explanation for why some molecular cloud regions collapse to form planetary systems that are rich in terrestrial planets, water, and possibly life while others do not. Historically, our understanding of planetary system formation has relied on astronomical observations of our Solar System. Much less appreciated, however, is the role that that the analysis of planetary materials (i.e. meteorites, cometary dust, and solar wind particles) has played in this understanding. In this talk, I will review how observations of our solar system at the chemical and isotopic level provided us with tight constraints on planetary system formation and the origins of water on terrestrial planets like our own. Incorporating these observations into comprehensive models, I argue, will require combining theoretical and laboratory studies of astrochemical processes that occur in molecular clouds and protoplanetary disks. To illustrate, I will highlight the recent accomplishments made by my research group and collaborators in understanding astrochemical processes with high precision chemical and isotopic resolutions. I conclude by highlighting recent advances in laboratory astrophysical measurement technology including the measurement of radiation induced isotope exchange between water ice and silicate surfaces at 10K, the direct measurement of the optical properties of individual dust grains from the Stardust mission in the laboratory using NanoIR, and the development of planetary exploration instrumentation for the in-situ determinations of the isotopic compositions of lunar ice. I will conclude by discussing how these studies may help us understand the origins of the planets and water in the solar system.

November 25, 2020

NOTE: No seminar today

December 2, 2020

 "Improving CMB foreground dust modeling by 3D mapping the magnetized ISM"

Gina Panopoulou
NASA Hubble Fellow

 Or iPhone one-tap :
US: +16699006833,,93051810865# or +12133388477,,93051810865#

Or Telephone:
Dial (for higher quality, dial a number based on your current location):
US: +1 669 900 6833 or +1 213 338 8477 or +1 669 219 2599

Webinar ID: 930 5181 0865

International numbers available:

ABSTRACT: Searches for primordial gravitational waves in the CMB are hindered by a major obstacle: foreground dust emission from the Galaxy. In order to surpass this obstacle, the foreground signal must be modeled and removed with unprecedented accuracy. To reach the required levels of precision we must reconstruct the -yet uncharted- 3D structure of the Galactic magnetic field. I will present first steps towards obtaining a tomographic mapping of the dusty, magnetized ISM, by using stellar polarization, astrometric distances and HI data. I will discuss how the use of these state-of-the art datasets can inform future foreground modeling efforts.

December 9, 2020

 "Simulations and Observations of the Circumgalactic Medium"

Ramona Augustin
Postdoctoral Fellow
Space Telescope Science Institute

 Or iPhone one-tap :
US: +16699006833,,98794103722# or +12133388477,,98794103722#

Or Telephone:
Dial (for higher quality, dial a number based on your current location):
US: +1 669 900 6833 or +1 213 338 8477 or +1 669 219 2599

Webinar ID: 987 9410 3722

International numbers available:

ABSTRACT: Understanding the processes of gas flows in and out of galaxies is crucial in galaxy evolution studies. Yet, observations of the faint and diffuse Circum-Galactic Medium (CGM), where these processes take place, remain challenging.

The most efficient approach to detect this faint and diffuse gas is in absorption towards bright background quasars. However, to investigate the CGM we need to also identify the galaxy counterpart and connect it to the absorption feature. In this context we characterized counterparts to Damped Lyman-alpha Absorbers (DLAs) at z~1 using HST broad-band images. We measured their stellar masses and find them to follow common galaxy scaling relations. We discovered their complex morphology and environments, challenging the interpretation of CGM studies in absorption.

Quasar absorbers are typically limited to a single sightline and hold no information on the spatial structure of the absorber. To overcome this limitation and gain information on the spatial structure and the nature of CGM absorbers, we combine IFU data with high-resolution cosmological FOGGIE simulations. We detect and analyze two MgII absorption systems at z~1 that show significant differences in their equivalent width variations towards the different sightlines. We find that these variations are consistent with expectations from inflow/outflow regions simulations.

Beyond absorption, prospects to map the CGM in emission will offer new information on its extent and clumpiness. To optimize observing strategies of the CGM in emission, we have made predictions from dedicated cosmological zoom-in RAMSES simulations. We post-processed galaxy halos with an emission model to create mock integral field observations. Using the instrument model, our results indicate that ELT/HARMONI will enter a regime of low surface brightness typical of the CGM which is not attainable with current facilities.

December 16, 2020

NOTE: No seminar today

Winter 2021

January 6, 2021

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

Matthew Povich
Associate Professor, Department of Physics and Astronomy
Cal Poly Pomona

 Or iPhone one-tap:
US: +12133388477,,93928292508# or +16692192599,,93928292508#
Or Telephone:
Dial (for higher quality, dial a number based on your current location):
US: +1 213 338 8477 or +1 669 219 2599 or +1 669 900 6833
Webinar ID: 939 2829 2508
International numbers available:

ABSTRACT: 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.

January 13, 2021

NOTE: No seminar today

January 20, 2021

 "The James Webb Space Telescope: Mission Status and the Path to Science"

Michael McElwain
JWST Project Scientist
NASA Goddard Space Flight Center

 Or iPhone one-tap:
US: +16692192599,,92297890358# or +16699006833,,92297890358#
Or Telephone:
Dial (for higher quality, dial a number based on your current location):
US: +1 669 219 2599 or +1 669 900 6833 or +1 213 338 8477
Webinar ID: 922 9789 0358
International numbers available:

ABSTRACT: The James Webb Space Telescope (Webb) is a large-aperture space telescope optimized for near- and mid-infrared observations covering 0.6-28.5 microns. This mission was originally conceived in the mid-1990s as an infrared complement and flagship successor to the Hubble Space Telescope. After earning the top recommendation of the 2000 Astrophysics Decadal Survey, this Observatory has had a remarkable development phase that will culminate in a launch later this year! I will provide a brief history of the Webb mission and highlight the technical milestones that were recently achieved. I will then describe the final ground testing activities, the launch segment, commissioning plans, and the Cycle 1 science program.

January 27, 2021

 "The Formation and Growth of Supermassive Black Holes"

Anna-Christina Eilers
NASA Hubble Fellow

 Or iPhone one-tap :
US: +16699006833,,94767960244# or +12133388477,,94767960244#
Or Telephone:
Dial (for higher quality, dial a number based on your current location):
US: +1 669 900 6833 or +1 213 338 8477 or +1 669 219 2599
Webinar ID: 947 6796 0244
International numbers available:

ABSTRACT: Observations of high-redshift quasars show that they host supermassive black holes (SMBHs) already less than ~1 Gyr after the Big Bang. It has been argued that in order to rapidly grow these SMBHs in such short amounts of cosmic time, they need to accrete matter over timescales comparable to the age of the universe, and thus the lifetime of quasars - the integrated time that galaxies shine as active quasars - is expected to be of order ~10^9 yr at z~6, even if they accrete continuously at the Eddington limit.

I will present a new method to obtain model-independent constraints on the lifetime of high-redshift quasars with unprecedented precision, based on measurements of the sizes of ionized regions around quasars, known as proximity zones. The sizes of these proximity zones are sensitive to the lifetime of the quasars, because the intergalactic gas has a finite response time to the quasars’ radiation. Applying this method to quasar spectra at z>6, we discover an unexpected population of very young quasars, indicating lifetimes of only ~10,000 years, which poses significant challenges on current black hole formation models. I will show results from our on-going multi-wavelength survey to detect and characterize young quasars and their environments. Furthermore, I will discuss several modifications to the current SMBH formation paradigm that might explain the results, e.g. super-critical mass accretion rates, massive initial black hole seeds in excess of stellar remnants, or highly obscured quasar growth phases. In the end I will show how we aim to disentangle the various scenarios by means of on-going and future IFU observations with MUSE and the James Webb Space Telescope, in order to shed new light onto the formation and growth of the first SMBHs in the universe.

February 3, 2021

Azalee Bostroem
UC President's Pre-Professoriate Fellow
UC Davis

February 10, 2021

February 17, 2021

February 24, 2021

March 3, 2021

March 10, 2021

March 17, 2021

Kaitlin Kratter
Associate Professor, Department of Astronomy
University of Arizona

Spring 2021

March 24, 2021

March 31, 2021

April 7, 2021

April 14, 2021

April 21, 2021

April 28, 2021

May 5, 2021

Lluis Mas Ribas
Postdoctoral Researcher in Astrophysics & Cosmology

May 12, 2021

Mark Vogelsberger
Associate Professor of Physics

May 19, 2021

May 26, 2021

June 2, 2021

June 9, 2021