Constraining the Galaxy-Halo Connection Through Accurate Modeling of Small-Scale Galaxy Clustering
Szewciw, Adam Orest
The Universe consists of structures of a wide variety of physical sizes. Over the last few decades, astronomers have succeeded in extensively cataloging this structure, both at the (relatively) small scales of stars within our galaxy and at the large scales of clusters and super-clusters of galaxies. Cosmology is the branch of astronomy concerned with how the large-scale observable structure of the Universe formed and evolved into what we see today. The dominant cosmological model, LCDM, posits that stars, gas, and all other directly observable matter in the Universe only comprise ~1/6 of the total mass in the Universe. The majority of the mass (~5/6) is dark matter, which only interacts through gravity and thus cannot be directly observed. At the largest physical scales, the formation of structure is dominated by gravitational interactions between massive bodies. Because dark matter makes up the majority of the mass, it is primarily responsible for the formation of large-scale structures we observe today. In LCDM, dark matter effectively serves as the skeleton of the Universe, with galaxies forming and evolving in high density, gravitationally bound regions of dark matter called "halos." Understanding the precise way in which galaxies occupy dark matter halos, or the "galaxy-halo connection," is an important area of research at the intersection of cosmology and galaxy theory. In this dissertation, I discuss efforts to better understand the galaxy-halo connection through use of a statistical model applied to cosmological N-body simulations. Employing this model, I constrain a particular form of the galaxy-halo connection when fit to observational data of the clustering of galaxies from the Sloan Digital Sky Survey. Compared to previous work using fewer clustering statistics, we find significant improvement in the constraints on all parameters of our model for two different luminosity-threshold galaxy samples. However, our best-fit model results in significant tension for both samples, indicating the need to add second-order features to our model. This work elucidates important features of the galaxy-halo connection and serves as a significant statistical advancement in studies which attempt to constrain the galaxy-halo connection through measurements of galaxy clustering.