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 Ly$\alpha$. 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 $10^8 M_\star/M_ødot łeq
10^10.5$, we find that $R_cross(M_\star) 2 0.6 R_\rm
vir$. Additionally, we find excellent agreement between $R_\rm
cross(M_\star)$ 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.
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