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Astrophysics Seminars


The UCSD-SDSU 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. Seminars take place on Wednesdays from 3:30 - 4:30 p.m. via Zoom until further notice. The seminar organizer is Prof. Karin Sandstrom.

Upcoming Seminars

Spring 2021

May 5, 2021

 "LIMFAST: a Semi-numerical Tool for Line Intensity Mapping"

Lluis Mas Ribas
Postdoctoral Researcher in Astrophysics & Cosmology

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ABSTRACT: Intensity Mapping is emerging as a new technique to study galaxy formation and evolution over cosmic time, and this creates a pressing need for multi-scale and multi-frequency simulation tools. LIMFAST is a simulation code designed for such a purpose, with emphasis on the epoch of cosmic reionization (z>5). LIMFAST builds on top of the 21cmFAST cosmological code, and it takes advantage of a semi-numerical scheme to enable multiple realizations of different galaxy models and reionization histories, over large cosmic volumes, and in a short time. We have implemented a flexible/customizable star-formation formalism into LIMFAST, accounting for Pop II and Pop III stellar components, as well as the metal enrichment of the galactic environment. LIMFAST then takes into account the properties of these simulated media and derives the emissivity for many emission lines via tabulated results from external photoionization computations. This approach will allow a variety of self-consistent multi-line studies of the high-redshift universe. I will discuss the details of the code and a set of initial results, as well as the variations and extensions that can be easily implemented into LIMFAST when released publicly to the community.

May 12, 2021

 "Simulating Structure and Galaxy Formation"

Mark Vogelsberger
Associate Professor of Physics

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ABSTRACT: Cosmological simulations of galaxy formation have evolved significantly over the last years.

In my talk I will describe recent efforts to model the large-scale distribution of galaxies with cosmological hydrodynamics simulations. I will focus on large-scale simulations like IllustrisTNG. After demonstrating the success of these simulations in terms of reproducing an enormous amount of observational data, I will also talk about their limitations and directions for further improvements over the next couple of years. Furthermore, I will also talk briefly about our new simulation campaign, the THESAN project, to study the epoch of re-ionization and the early Universe.

May 19, 2021

 "Characterizing the Atmospheres of Low-Metallicity Brown Dwarfs"

Eileen Gonzales
51 Pegasi b Postdoctoral Fellow
Cornell University

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ABSTRACT: Ultracool Subdwarfs, objects that have metallicities significantly lower than that of the Sun and ages > 5Gyr, provide insight into understanding how metallicity affects observable features of low-mass stars and brown dwarfs. Currently, substellar subdwarfs are thought to have cloudless atmospheres due to reduced condensate opacities from their low metallicities. In this talk, I aim to explore the nature of clouds in subdwarfs using both observational and theoretical approaches I ask: (1) Are subdwarfs cloudless? and (2) How does their thermal profile compare to objects of similar effective temperature (Teff) or spectral type? By creating distance-calibrated spectral energy distributions (SEDs), I will compare one of the bluest known subdwarfs, SDSS J1256, to various aged sources of similar Teff and/or bolometric luminosity to examine the overall SED shape and features in the NIR bands, as well as compare fundamental parameters and place SDSS J1256 in context with the larger subdwarf population. To explore the nature of clouds in subdwarfs, I use the Brewster retrieval framework to examine a sample of subdwarfs and comparative sources to explore what may be causing the differences seen in the SEDs of these sources. In this talk, I will discuss the results for the widely separated co-moving low-mass d/sdL7+T7.5p pair SDSS J1416+1348AB to determine if the pair formed and evolved together and their cloud properties. Additionally, I will discuss preliminary results from a comparative sample of field sources of similar temperature or spectral type to SDSS J1416A to determine how the PT profile of these objects compares and what may drive the differences we see in their spectra.

May 26, 2021

Aaron J. Rosengren
Assistant Professor, Mechanical & Aerospace Engineering

June 2, 2021

June 9, 2021