Abstract

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 Me < Må < 1011 Me and z ≲ 0.5, we show that the H I covering fraction above a threshold of NHI > 1014cm−2 is ≳0.5 within 1.5 virial radii (Rvir ∼ R200m). 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, RCGM14 , as a function of galaxy mass. RCGM14 is the impact parameter at which the probability of observing an absorber with NHI >1014 cm−2 is >50%. In this framework, the radial extent of the CGM of Må > 109.9 Me galaxies is RCGM14 = 346-+5357 kpc or RCGM14 ~ 1.2Rvir. Intermediate-mass galaxies with 109.2 < Må/Me < 109.9 have an extent of RCGM14 = 353-+5064 kpc or RCGM14 ~ 2.4Rvir. Low-mass galaxies, Må < 109.2 Me, show a smaller physical scale of RCGM14 = 177-+6570 kpc and extend to RCGM14 ~ 1.6Rvir. Our analysis suggests that using Rvir as a proxy for the characteristic radius of the CGM likely underestimates its extent.