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

We present initial results from the Cosmic Origins Spectrograph (COS) and Gemini Mapping the Circumgalactic Medium (CGMCGM equivalent to CGM(2)) survey. The CGM(2) survey consists of 1689 galaxies, all with high-quality Gemini-GMOS spectra, within 1 Mpc of 22 z less than or similar to 1 quasars, all with a signal-to-noise ratio of similar to 10 Hubble Space Telescope/COS G130M+G160M spectra. For 572 of these galaxies with stellar masses 10(7) M-circle dot < M-star < 10(11) M-circle dot and z less than or similar to 0.5, we show that the H I covering fraction above a threshold of N-HI > 10(14)cm(-2) is greater than or similar to 0.5 within 1.5 virial radii (R-vir similar to 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-CGM(14), as a function of galaxy mass. R-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-star > 10(9.9) M-circle dot galaxies is R-CGM(14) = 346(-53)(+57) kpc or R-CGM(14) similar or equal to 1.2R(vir). Intermediate-mass galaxies with 10(9.2) < M-star/M-circle dot < 10(9.9) have an extent of R-CGM(14) = 353(-50)(+64) kpc or R-CGM(14) similar or equal to 2.4R(vir). Low-mass galaxies, M-star < 10(9.2) M-circle dot, show a smaller physical scale of R-CGM(14) = 177(-65)(+70) kpc and extend to R-CGM(14) similar or equal to 1.6R(vir). Our analysis suggests that using Rvir as a proxy for the characteristic radius of the CGM likely underestimates its extent.

Automated summary

This study presents initial findings from the COS and CGMCGM (or CGM(2)) survey on the circumgalactic medium (CGM) surrounding galaxies. The research reveals that the characteristic size of the CGM varies for galaxies of different mass ranges, with lower mass galaxies having smaller CGM radii and higher mass galaxies having larger CGM radii. The use of Rvir as a proxy for the CGM's characteristic radius is suggested to underestimate its overall extent.