Molecular Gas in the Early Universe
Abstract
The manner by which gas in the early universe formed the stars and galaxies at the current epoch is poorly understood. To understand better the processes involved, we have studied high-redshift molecular gas reservoirs out of which stars and galaxies are expected to eventually form. In this dissertation we present both observations of molecular species at high redshift and theoretical models which calculate the evolution of molecular abundances. These studies address fundamental questions such as the mass, size, structure, and composition of protogalactic systems. For a sample of 22 northern damped Ly alpha systems at redshifts z > 2.4, we detect CO emission in one source, 1643 + 4631A. The inferred molecular gas mass for 1643 + 4631A is ~1012M_ ⊙. We also detect CO emission associated with the 21-cm absorption line system at z = 0.437 toward 3C 196. The molecular gas mass detected in this system is ~10^ {11}Modot. Hence, the radio observations for these two QSO absorption line systems imply a large molecular gas mass of M_ {gas}~10^{11 -12}Modot and suggest that these systems represent a protogroup of galaxies spread over _sp{~}> 200 kpc. In addition to providing several observational results pertaining to molecular gas at high redshift, we also present theoretical models predicting the molecular composition in young galactic systems. Unlike galaxies at the current epoch where M_{stars } >> Mgas, nascent galactic systems are expected to be gas rich ( Mstars~ M_{gas }). The peak of gaseous metals is predicted to occur when approximately one half of the total baryonic mass is stars and the other half is gas, which, depending on cosmology and the adopted star formation parameters, corresponds to redshifts of z ~ 2-3. Since the oxygen abundance is expected to be much greater than the carbon abundance in the young galactic systems, oxygen bearing molecules, such as O_2, could be prevalent at early cosmological epochs. However, the predicted molecular abundances in young galactic systems depend sensitively on several unknown factors including the effects of metallicity, photodissociation, turbulent mixing, and grain processes. Future observations of molecular and atomic species at millimeter and submillimeter wavelengths should constrain the theoretical models of chemical evolution and nucleosynthesis within the earliest generations of stars and provide insight into the structure and composition of protogalactic systems.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- January 1996
- Bibcode:
- 1996PhDT.........2F
- Keywords:
-
- REDSHIFTS;
- GALAXIES;
- Physics: Astronomy and Astrophysics