2021ApJ...912....9W

We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM²) survey. The CGM² survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z <= 1 quasars, all with a signal-to-noise ratio of ∼10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 10⁷ M_☉ < M_* < 10¹¹ M_☉ and z <= 0.5, we show that the H I covering fraction above a threshold of N_HI > 10¹⁴cm^–2 is >=0.5 within 1.5 virial radii (R_vir ∼ R_200m). We examine the H I kinematics and find that the majority of absorption lies within ±250 km s^–1 of the galaxy systemic velocity. We examine H I covering fractions over a range of impact parameters to infer a characteristic size of the CGM, R_CGM¹⁴, as a function of galaxy mass. R_CGM¹⁴ is the impact parameter at which the probability of observing an absorber with N_HI >10¹⁴ cm^–2 is >50%. In this framework, the radial extent of the CGM of M_* > 10^9.9 M_☉ galaxies is R_CGM¹⁴=346_–53⁺⁵⁷ kpc or R_CGM¹⁴≃1.2R_vir. Intermediate-mass galaxies with 10^9.2 < M_*/M_☉ < 10^9.9 have an extent of R_CGM¹⁴=353_–50⁺⁶⁴ kpc or R_CGM¹⁴≃2.4R_vir. Low-mass galaxies, M_* < 10^9.2 M_☉, show a smaller physical scale of R_CGM¹⁴=177_–65⁺⁷⁰ kpc and extend to R_CGM¹⁴≃1.6R_vir. Our analysis suggests that using R_vir as a proxy for the characteristic radius of the CGM likely underestimates its extent.