CGM2 I: The extent of the circumgalactic medium traced by neutral hydrogen

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

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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.

Original languageEnglish
Article number9
JournalAstrophysical Journal
Issue number1
StatePublished - 1 May 2021


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