CGM$^2$ $+$ CASBaH: The Mass Dependence of H~I Ly$α$-Galaxy Clustering and the Extent of the CGM

Abstract

We combine datasets from the CGM 2 and CASBaH surveys to model a transition point, R cross , between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies at z < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01 − 20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H I Lyα. Our best-fitting model is an exclusionary two-component model that combines a 3D absorber-galaxy cross correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of R cross as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 10 8 ≤ M /M ≤ 10 10.5 , we find that R cross (M ) ≈ 2 ± 0.6R vir . Additionally, we find excellent agreement between R cross (M ) and the theoretically-determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at z < 0.5 that distribute T ≈ 10 4 K gas to distances beyond the virial radius.