  Luminous 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 structure. 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. We use the 25 square degree Early Data Release (EDR) of 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. We use a new
statistical background technique to identify excess populations of putative
satellite galaxies around 1823 LRGs at 0.2<z<0.65. In three redshift and
luminosity bins we measure the numbers of satellite galaxies and their r- color
distribution down to rest-frame $g$-band luminosity limits at least 3.6 times
fainter than L*. In addition, we develop a forward modeling technique and apply
it to constrain the mean number of satellites in each of our redshift and
luminosity bins. Finally, we use these estimates to determine the amount of
stellar mass growth in LRGs down to the local Universe.
