2021 journal article
CGM(2) I: The Extent of the Circumgalactic Medium Traced by Neutral Hydrogen
ASTROPHYSICAL JOURNAL, 912(1).
Abstract We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM ≡ CGM 2 ) survey. The CGM 2 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 10 7 M ⊙ < M ⋆ < 10 11 M ⊙ and z ≲ 0.5, we show that the H i covering fraction above a threshold of N HI > 10 14 cm −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, <?CDATA ${R}_{\mathrm{CGM}}^{14}$?> , as a function of galaxy mass. <?CDATA ${R}_{\mathrm{CGM}}^{14}$?> is the impact parameter at which the probability of observing an absorber with N HI >10 14 cm −2 is >50%. In this framework, the radial extent of the CGM of M ⋆ > 10 9.9 M ⊙ galaxies is <?CDATA ${R}_{\mathrm{CGM}}^{14}={346}_{-53}^{+57}$?> kpc or <?CDATA ${R}_{\mathrm{CGM}}^{14}\simeq 1.2{R}_{\mathrm{vir}}$?> . Intermediate-mass galaxies with 10 9.2 < M ⋆ / M ⊙ < 10 9.9 have an extent of <?CDATA ${R}_{\mathrm{CGM}}^{14}={353}_{-50}^{+64}$?> kpc or <?CDATA ${R}_{\mathrm{CGM}}^{14}\simeq 2.4{R}_{\mathrm{vir}}$?> . Low-mass galaxies, M ⋆ < 10 9.2 M ⊙ , show a smaller physical scale of <?CDATA ${R}_{\mathrm{CGM}}^{14}={177}_{-65}^{+70}$?> kpc and extend to <?CDATA ${R}_{\mathrm{CGM}}^{14}\simeq 1.6{R}_{\mathrm{vir}}$?> . Our analysis suggests that using R vir as a proxy for the characteristic radius of the CGM likely underestimates its extent.