CGM2 I: The Extent of the Circumgalactic Medium Traced by Neutral Hydrogen

• Published in: The Astrophysical journal Vol. 912; no. 1
• Main Authors: Wilde, Matthew C., Werk, Jessica K., Burchett, Joseph N., Prochaska, J. Xavier, Tchernyshyov, Kirill, Tripp, Todd M., Tejos, Nicolas, Lehner, Nicolas, Bordoloi, Rongmon, O’Meara, John M., Tumlinson, Jason
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.05.2021; IOP Publishing
• Subjects: Astronomy data analysis; Astronomy databases; Astrophysics; Circumgalactic medium; Extragalactic astronomy; Galaxies; Galaxy structure; Hubble Space Telescope; Hydrogen; Intergalactic medium; Kinematics; Parameters; Polls & surveys; Quasar absorption line spectroscopy; Quasars; Signal to noise ratio; Space telescopes; Stars & galaxies
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/abea14

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, \({R}_{\mathrm{CGM}}^{14}\), as a function of galaxy mass. \({R}_{\mathrm{CGM}}^{14}\) 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 ⋆ > 109.9 M ⊙ galaxies is \({R}_{\mathrm{CGM}}^{14}={346}_{-53}^{+57}\) kpc or \({R}_{\mathrm{CGM}}^{14}\simeq 1.2{R}_{\mathrm{vir}}\). Intermediate-mass galaxies with 109.2 < M ⋆/M ⊙ < 109.9 have an extent of \({R}_{\mathrm{CGM}}^{14}={353}_{-50}^{+64}\) kpc or \({R}_{\mathrm{CGM}}^{14}\simeq 2.4{R}_{\mathrm{vir}}\). Low-mass galaxies, M ⋆ < 109.2 M ⊙, show a smaller physical scale of \({R}_{\mathrm{CGM}}^{14}={177}_{-65}^{+70}\) kpc and extend to \({R}_{\mathrm{CGM}}^{14}\simeq 1.6{R}_{\mathrm{vir}}\). Our analysis suggests that using R vir as a proxy for the characteristic radius of the CGM likely underestimates its extent.