From x-ray clusters to galactic spheroids: Semi-analytic modeling of the origin of structure in the universe

In this thesis, we use semi-analytic techniques to examine the origin of structure in the universe.; In the first part of this thesis, we compare how two competing theories, adiabatic Gaussian CDM and textures+CDM, perform in explaining observations of X-ray clusters and of the rms level of mass fluctuations as measured by large-scale flows. Because clusters are rare events, comparing the level of rms fluctuations with the X-ray cluster abundances directly probes the shape of the probability distribution function (PDF) of the initial density field. We conclude that texture models, which have exponential PDFs, are disfavored relative to Gaussian models. We also find evidence for the presence of systematic errors in the measurements of the rms. A second test uses the shape of the temperature distribution of X-ray clusters to probe both the PDF and the power spectrum of density perturbations. From this test, we conclude that high values of the density parameter {dollar}Omegasb0{dollar} are strongly disfavored in both Gaussian and texture models. Thus only models with a Gaussian PDF and values of {dollar}Omegasb0 approx 0.3{dollar} are consistent with all of the observational tests we have performed.; The second part of this thesis develops a model for the recent thermal and ionization history of the universe. After checking the results against numerical simulations, we analyze the evolution of the universe assuming different models for the initial density field. We find that the thermal and ionization history of the universe is sensitive to the power spectrum at scales of {dollar}sim{dollar}0.01-0.1{dollar}hsp{lcub}-1{rcub}{dollar}Mpc. Reheating begins significantly later in adiabatic Gaussian CDM models than in texture CDM or non-Gaussian isocurvature CDM models. Because of clumping, reionization occurs in all cases at a redshift {dollar}z sim 10.{dollar} We consider the effect of reionization on the cosmic microwave background radiation, as well as on the composition of the intergalactic medium. We calculate the evolution of the clustering bias of baryonic and luminous objects, finding that feedback from star formation appears to play an important role. Finally, we use the results of our analysis to speculate on the evolution and formation of galactic spheroids.