Galaxy Formation Near the Epoch of Reionization

Citation

Santos, Michael Robert (2004) Galaxy Formation Near the Epoch of Reionization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/X9XT-YT35. https://resolver.caltech.edu/CaltechETD:etd-05182004-154315

Abstract

I present five explorations of the formation of early galaxies near the epoch of reionization: observable phenomena that demonstrate the interaction between galaxy formation and the intergalactic medium.

I calculated the contribution of the first stars (Pop III) to the cosmic infrared background (CIRB). Pop III stars produced the observed unexplained component of the NIR CIRB if they were very massive and formed efficiently over a redshift range 25 ≳ z ≳ 7. A small escape fraction of ionizing photons from the nebular gas immediately surrounding the Pop III stars enhances the Pop III CIRB signal.

I calculated the effect of radiative transfer through the intergalactic medium (IGM) on the observed properties of Lyman alpha emission lines from z ≳ 6 galaxies. The detection of a Lyman alpha emitting galaxy at z = 6.5 resulted in claims that the universe was mostly ionized there. With existing information about the source galaxy it is almost impossible to deduce the ionization state of the z = 6.5 IGM, especially if there were galactic-scale super-winds.

I present a method to infer the stellar population responsible for completing reionization. We simulated helium and hydrogen absorption along lines-of-sight toward high-redshift QSOs assuming either Pop II or Pop III stars dominated the UV background at z=5. The final SDSS quasar sample may contain a quasar/line-of-sight combination that constrains the nature of the dominant ionizing sources only 300 Myr after the end of reionization.

I present an observational survey of low-luminosity Lyman alpha emitting galaxies at 4.5 < z < 6.7. This unprecedented survey utilized strong lensing by rich clusters of galaxies at intermediate redshifts to discover six likely Lyman alpha emitting galaxies. The z ~ 5 Lyman alpha luminosity function may be flatter than the mass function of dark matter halos, a sign of suppression of the star-formation efficiency in low-mass halos. However, our data by themselves are consistent with the slope of the halo mass function.

I modeled the formation of metal-poor globular cluster systems (GCSs), invoking reionization to explain the bimodality observed in GCS metallicity distributions. The model reproduces the mass and spatial extent of the Milky Way metal-poor GCS, and also the increasing number of metal-poor globular clusters per unit galaxy mass for galaxies in richer environments, as observed.

Thesis Files