Galaxies and their Circumgalactic Media at the Edge of Reionization

New Mexico State University, Las Cruces NM

Investigators

Abstract

During the first billion years, stars, galaxies, and quasars ionized and heated the hydrogen gas located between galaxies; most of the Universe has remained in a plasma state ever since. Finlator and collaborators will investigate whether elusive, faint galaxies dominated this process. The team will compare observations of galaxies and their circumgalactic media (CGM) to a series of theoretical "Technicolor Dawn" simulations to quantify the abundance of faint galaxies and learn about their stars. Coordinators from the New Mexico Alliance for Minority Participation (AMP) program will assist in recruiting an undergraduate student to participate in a hands-on research experience. Finlator and colleagues will simulate the galaxies, their CGM, the ultraviolet background, and the progress of reionization using cosmological simulations incorporating a spatially-resolved, multifrequency radiation transport solver. The team will determine how many galaxies (not just the nearest galaxy) are required to provide the metals for each high-ionization absorber. This will include an analysis of the galaxy masses and luminosities to investigate which galaxy populations are traced by metal absorbers and how this varies with ion and absorber strength. A Bayesian Information Criterion analysis using ensemble statistics of absorbers will probe the galaxy mass function. This will resolve the inconsistency between older simulations, which required high numbers of faint galaxies, and observations of absorbers’ environments indicating that faint galaxies are rare. The team will also apply observational constraints to the reionization-epoch Initial Mass Function (IMF). For example, strong high-ionization absorbers that trace galaxy-poor environments may indicate a hard ionizing background, but a tail of even stronger absorbers could indicate a "top-heavy" IMF rich in massive stars. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.