Rudnick, GregoryTownsend, Melinda2025-02-102025-02-102023-05-312023http://dissertations.umi.com/ku:18785https://hdl.handle.net/1808/35918Luminous Red Galaxies, or LRGs, are representative of the most massive galaxies and were originally selected in the Sloan Digital Sky Survey as good tracers of large scale struc- ture. They are dominated by by uniformly old stellar populations, have low star formation rates, early type morphologies, and little cold gas. Despite having old stellar populations and little in situ star formation, studies have shown that they have grown their stellar mass since z=1, implying that they grow predominantly via the accretion of satellites. Tests of this picture have been limited because of the lack of deep imaging data sets that both covers a large enough area of the sky to contain substantial numbers of LRGs and that also is deep enough to detect faint satellites. I use the DESI Legacy Imaging Surveys to characterize the satellite galaxy population of LRGs out to z=0.65. The DESI Legacy Imaging Surveys are comprised of grz imaging to 2-2.5 mag deeper than SDSS and with better image quality. I use a new statistical background technique to identify excess populations of putative satel- lite galaxies around over 90,000 LRGs at 0.2 < z < 0.65. In three redshift and luminosity bins I measure the numbers of satellite galaxies and their r − z color distribution down to rest-frame g-band luminosity limits at least 3.6 times fainter than L∗. In addition, I develop a forward modeling technique and apply it to constrain the mean number of satellites in each of our redshift and luminosity bins. Finally, I use these estimates to determine the amount of stellar mass growth in LRGs down to the local Universe.116 pagesenCopyright held by the author.AstrophysicsAstronomyelliptical galaxiesgalaxy evolutionluminous red galaxiessatellite galaxiesDissertation0000-0002-8764-740X