Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astronomy

First Advisor

van den Bosch, Frank

Abstract

Most cosmological analyses of galaxy surveys under-utilize the data from the smallest scales. Firstly, analytical calculations become challenging in the fully non-linear regime. Moreover, the small scales are inherently plagued by several systematic uncertainties, such as the effects of baryons. Interestingly, analyses that have delved into the non-linear regimes of structure formation, mostly using galaxy clustering or weak gravitational lensing, often show an ongoing tension with the probes of early Universe physics, such as the cosmic microwave background, about the exact values of some of the cosmological parameters. This begs the following questions: (a) Can we think of a new and alternative probe to constrain the link between galaxies and matter distribution in the Universe using data in the smallest scales of galaxy surveys? And (b) can we develop a new and complementary way to infer cosmology from galaxy survey data, that bypasses the usual systematics? To that end, kinematics of satellite galaxies, although a very old technique, has rarely been utilized. In this dissertation, I develop and improve Basilisk, a novel Bayesian hierarchical way of modelling satellite galaxy kinematics to constrain the galaxy-halo connection. After extensively testing the machinery against realistic mock data, I apply Basilisk to SDSS data to constrain with extreme precision the central and satellite galaxy-halo connections, the satellite radial profile, and their orbital anisotropy. I use Basilisk to further test the standard galaxy-halo connection model itself, and build extensions to construct a more flexible data-driven model. Finally, I develop a technique, using Basilisk, to constrain cosmological parameters in a completely novel way that is free from halo assembly bias, incorporates baryonic effects, and is complementary to standard methods based on clustering and lensing. Using a fiducial model for the baryonic effects, I show that the cosmology inferred using Basilisk is in perfect agreement with the constraints from the cosmic microwave background. Looking ahead, Basilisk is the ideal tool to optimally extract information from the smallest scales of upcoming galaxy redshift surveys, which will map out the Universe in unprecedented detail.

Download

Share

COinS