| Monday, November 04, 2024 |
12:00pm |
Two Talks |
Mahan Mirza Khanlari, The University of Texas at Austin
Probing Neutral Hydrogen in the Circumgalactic Medium of LAEs in HETDEX
Abstract
The circumgalactic medium (CGM) is a critical yet elusive component in our understanding of galaxy evolution, acting as the interface between galaxies and large-scale structures in the universe. Traditional studies of the CGM rely on quasar sightlines, which, while informative, are limited by alignment constraints and offer only narrow lines of sight into these vast regions. In this talk, I will introduce a method to probe neutral hydrogen (H I) in the CGM of high-redshift Lyman-alpha emitters (LAEs) through spectral stacking without relying on quasar sightlines. Utilizing data from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)—a blind integral field unit (IFU) survey—we harness the integrated light from background galaxies to detect Lyman-alpha absorption signatures in the CGM of over 55,000 LAEs at z ~ 2.5. By measuring the strength and variability of this absorption as a function of impact parameter and local density, we can infer an empirical H I density profile for the CGM of LAEs.
Hector Cruz, Johns Hopkins University
The First Billion Years in Seconds: An Effective Model for the 21-cm Signal with Population III Stars
Abstract
In the next few years, observations of the 21-cm signal will open a window to the cosmic dawn epoch, when the first stars formed. It is conventional to interpret these observations through semi-numerical or hydrodynamical simulations, which are often computationally intensive and inflexible to exotic cosmological or astrophysical effects. I will present a new approach to predict the 21-cm global signal and fluctuations in the presence of PopIII stars in seconds. PopIII stars, residing in low-mass molecular-cooling halos, are highly sensitive to feedback, especially from H2-dissociating Lyman-Werner radiation and dark matter-baryon relative velocities. To bypass expensive numerical simulations, we develop an effective prescription of the star formation rate density in the presence of PopIII stars. Our method recovers the full nonlinear distributions of radiative fields that determine the 21-cm signal including anisotropic feedback. I will show how PopIII stars impact the 21-cm global signal and power spectrum across cosmic time and at different distance scales. I will also highlight how the spatial modulation of the relative velocities induces Velocity Acoustic Oscillations in 21-cm power spectra, providing us with a new and robust cosmological standard ruler. Our public code, Zeus21, can predict 21-cm observables in seconds, presenting a meaningful first step towards rapid precision astrophysics and cosmology in the first billion years.
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| Monday, November 11, 2024 |
12:00pm |
Two Talks |
Alexa Morales, The University of Texas at Austin
Rescheduled to Spring 2025 semester
Laurel Weiss, The University of Texas at Austin
Using Lyman Alpha Absorption to Measure the Intensity and Variability of z ∼ 2.4 Ultraviolet Background Light
Abstract
We present measurements of z ∼ 2.4 ultraviolet background light using Lyα absorption from galaxies at z ∼ 2−3 in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) database. Due to the wide area of this survey, we also measure the variability of this light across the sky. The data suggest an asymmetric geometry where integrated ultraviolet light from background galaxies is absorbed by H I within the halo of a foreground galaxy, in a configuration similar to damped Lyα systems. Using over 400,000 high quality LAE spectra available in HETDEX, this weak absorption signal is detectable via spectral stacking and becomes negative due to the experiment’s sky subtraction procedure. The amount that the absorption is over-subtracted is representative of the z ∼ 2.4 UV contribution to the overall extragalactic background light (EBL) at Lyα. Using this method, we determine an average intensity of 12.9 ± 3.7 nW m−2 sr−1 at a median observed wavelength of 4134 ˚A, or a rest-frame UV background intensity of 508 ± 145 nW m−2 sr−1 at z ∼ 2.4. We find that this flux varies significantly depending on the density of galaxies in the field of observation. Our estimates are consistent with direct measurements of the overall EBL.
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| Monday, November 18, 2024 |
12:00pm |
Two Talks |
Joohyun Lee, The University of Texas at Austin
The Inhomogeneous Rise of Metallicity During the Epoch of Reionization in the Cosmic Dawn III simulation
Abstract
When galaxies and stars began to form, they released ionizing radiation into the intergalactic medium which resulted in its reionization over the course of the first billion years. This ionizing radiation was dominated by massive stars. The same massive stars that released this ionizing radiation responsible for reionization also formed and released heavy elements when they exploded as supernovae, enriching the metal-free primordial gas both inside galaxies and outside them, by driving winds into the surrounding IGM. Just as reionization was inhomogeneous, so must the rise of metallicity during the EoR have been. The theory of this inhomogeneous rise of metallicity is, therefore, inseparable from the theory of reionization, and predicting its observable consequences requires us to model both processes, together, self-consistently. We have analyzed the results of the latest state-of-the-art radiation-hydro simulation of fully-coupled galaxy formation and reionization by The Cosmic Dawn (“CoDa”) Project, CoDa III, including its self-consistent tracking of the inhomogeneous rise of metallicity through the end of the EoR and beyond. We will present these CoDa III results for the inhomogeneous evolution of metallicity in the universe and its observable consequences.
Oscar Chavez Ortiz, The University of Texas at Austin
The T.E.S.L.A. Survey: Connecting Lyman-alpha Emission to Galaxy Properties
Abstract
The epoch of reionization (EoR) is the last major phase change that the universe has undergone and many unanswered questions remain pertaining to the reionization history. To accurately constrain the reionization history requires precise measurements of the neutral hydrogen fraction during the EoR. Lyman-alpha is a great tracer of neutral Hydrogen due to its large interaction cross section and has been used to measure the neutral fraction above redshift 6. To do this analysis requires accurate measurement of the emergent Lyman-alpha flux of galaxies during the EoR. However, at these redshifts it becomes increasingly difficult to measure how much Lyman-alpha a galaxy is emitting due to Lyman-alpha interacting with neutral hydrogen in the surrounding IGM. In this talk, I will show work done on the T.E.S.L.A. survey which is studying a sample of tens of thousands of Lyman-alpha emitting galaxies (LAEs) across the CEERS, COSMOS-UDS, COSMOS-PRIMER, SHELA and the NEP field to tie the physical properties of LAEs to emergent Lyman-alpha emission.
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| Monday, November 25, 2024 |
12:00pm |
Fall Break - no talk scheduled |
Fall Break - no talk scheduled
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| Monday, December 02, 2024 |
12:00pm |
No talk scheduled |
No talk scheduled
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| Monday, December 09, 2024 |
12:00pm |
Two Talks |
Hollis Akins, The University of Texas at Austin
Title: TBA
Ansh Gupta, The University of Texas at Austin
Title: TBA
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