The Formation of Galaxies from Gas

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

ABSTRACT AST 0098492 Rauch How do galaxies form? Studies show that the Quasars (QSOs) have many high redshift absorption lines from elements heavier than Helium in their spectra. Most current theories indicate that the chemical elements which give rise to these absorption lines must have been made in stars formed after the Big Bang (the so called Pop III stars). Yet when observed in quasar spectra, these absorption lines show that the metal enriched gas must be in clouds which lie between us and the QSOs. The goal of this project is to try and understand the role of this gas in galaxy formation in the early universe, at high redshift. This program is designed to complement traditional studies of galaxy formation where the emphasis has been more on the formation and fate of the stars in galaxies during the early merger or clustering process. Over the past decade, cosmological hydrodynamic computer simulations have shown that most of the early stages of galaxy formation (in particular the "dark" ones, before stars started to shine) can be observed using the absorption lines which they form in the spectra of background QSOs. The velocity structure of these lines shows infall of gas and protogalactic fragments, from the turnaround of perturbations in the intergalactic medium, as well as stellar feedback into the gas and the gasdynamics of the high redshift interstellar medium itself. The aim of this program is to use the observed properties of these low density, high ionization absorption lines to understand the relation between galaxies and gaseous inflows and outflows at high redshift. The statistics of the observed absorption systems (to be obtained from several large telescopes) will be interpreted with the help of state-of-the-art cosmological hydrodynamic -simulations. The clustering properties of metal lines on large scales will be used to trace the high redshift large scale structure at densities much lower than those probed by bright high redshift sources (e.g. radio galaxies, QSOs, Lyman-break galaxies). Absorption line profiles will be examined to determine the kinematics of the gas, and attempts will be made to identify the precise origin of the gas phases revealed by various metal absorption lines and to directly observe the infall of matter into forming galaxies. Observations of absorption systems in very close multiple lines of sight to lensed QSOs will help to quantify the density and velocity structure of the metal enriched gas near the potential wells of young galaxies. Measures of the turbulence of the gas will decide to what degree the surprisingly widespread metal enrichment of the intergalactic medium is a recent process or the result of an ancient Population III phase of starformation. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC). ***