Galaxies and Cosmology Seminar

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Galaxies and Cosmology Seminar - Two Talks

Monday, September 13, 2021, 12:00pm - 01:00pm

This repeat is an exception to the normal repeat pattern

Joohyun Lee, The University of Texas at Austin
Dark Matter Deficient Galaxies and Their Member Star Clusters Form Simultaneously during High-velocity Galaxy Collisions in 1.25 pc Resolution Simulations

Abstract

How diffuse dwarf galaxies that are deficient in dark matter—such as NGC1052-DF2 and NGC1052-DF4—formed remains a mystery. Along with their luminous member globular clusters (GCs), the so-called dark matter deficient galaxies (DMDGs) have challenged observers and theorists alike. Here we report a suite of galaxy collision simulations using the adaptive mesh refinement code ENZO with 1.25 pc resolution, which demonstrates that high-velocity galaxy collisions induce the formation of DMDGs and their star clusters (SCs) simultaneously. With a numerical resolution that is significantly better than our previous study, we resolve the dynamical structure of the produced DMDGs and the detailed formation history of their SCs, which are possible progenitors of the DMDG’s member GCs. In particular, we show that a galaxy collision with a high relative velocity of ∼300 km/s, invoking severe shock compression, spawns multiple massive SCs (Mstar < 10^6 Msun) in < 150 Myr after the collision. At the end of the ∼800 Myr evolution in our fiducial run, the resulting DMDG of Mstar ~ 3.5×10^8 Msun hosts 10 luminous Mv < −8.5 mag, gravitationally bound SCs with a line-of-sight velocity dispersion 11.2 km/s. Our study suggests that DMDGs and their luminous member SCs could form simultaneously in high-velocity galaxy collisions while being in line with the key observed properties of NGC1052-DF2 and NGC1052-DF4.

Grace Olivier, The Ohio State University
Evolution of Stellar Feedback from Reionization to The Milky Way: A Diverse Toolset of Imaging, Spectroscopy, and Modelling for Understanding the Impact of Massive Stars

Abstract

Massive stars contribute incredible amounts of energy to their surroundings across a variety of environments in the universe. Before their exciting deaths, massive stars produce feedback through a number of mechanisms that are frequently used in subgrid physics models in galaxy simulations to create realistic galaxies. Observations are a key to anchoring these simulations in reality, but there has been limited work on this front, especially for the youngest, embedded HII regions. I explore the effects of direct radiation pressure, dust-processed radiation pressure, photoionization heating and shock-heating from stellar winds in a sample of young HII regions (sources with radii < 0.5 pc) and determine which is the most important for very young stars. This analysis suggests radiative feedback on dust drives the earliest stages of HII region expansion. Additionally, I study the effects of radiative feedback in an exciting population of extremely low-metallicity star-forming galaxies that have been discovered in the local universe which are analogues to Reionization Era galaxies. During the Epoch of Reionization radiative feedback played a significant role in shaping the universe, and such analogues give us a detailed laboratory to explore the effects from feedback. I present deep FUV and optical spectra of two of these extreme emission line galaxies that have strong very-high-ionization optical and FUV emission lines (e.g., CIV, HeII, [FeV], [ArIV]). I demonstrate that canonical photoionization models, using typical stellar population models, catastrophically fail to reproduce the high-ionization emission lines. I constrain the stellar population properties using the FUV spectral features and explore the deficiencies of current stellar models. By simultaneously fitting the stellar and nebular emission within these extremely high-ionization emission line galaxies, I provide new observational benchmarks of radiative feedback for the next generation of stellar models at very low metallicity. By studying the effects of stellar feedback from single stars in the Milky Way to entire stellar populations in analogues to the first galaxies we can begin to build a coherent picture of stellar feedback as it impacts the vast scales of the universe.

Location: Online