CGM2 + CASBaH: The Mass Dependence of H i Lyα-Galaxy Clustering and the Extent of the CGM

Matthew C. Wilde, Kirill Tchernyshyov, Jessica K. Werk, Todd M. Tripp, Joseph N. Burchett, J. Xavier Prochaska, Nicolas Tejos, Nicolas Lehner, Rongmon Bordoloi, John M. O’Meara, Jason Tumlinson, J. Christopher Howk

Research output: Contribution to journalArticlepeer-review


We combine data sets from the CGM2 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 a 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 108 ≤ M /M ≤ 1010.5, we find that R cross(M ) ≈ 2.0 ± 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 ≈ 104K gas to distances beyond the virial radius.

Original languageEnglish
Article number114
JournalAstrophysical Journal
Issue number2
StatePublished - 1 May 2023


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