📝 SummarXiv

Abstract

We present new results on the spatial structure and kinematics of the circumgalactic medium (CGM) of z ~ 2 star-forming galaxies drawn from the Keck Baryonic Structure Survey, using Lya and metallic ion absorption recorded in spectra of background galaxies whose sightlines are projected within ~ 30" (physical distances D_tran < 250 kpc) of the foreground galaxy. The sample of 1033 foreground galaxies (<z_fg> = 2.03; 8 < log(M_star/M_sun) < 11) is probed by the spectra of 736 background galaxies obtained using Keck/KCWI (R ~ 1800) and Keck/LRIS (R ~ 1200). Using the galaxy pair ensemble, we present measurements of absorption strength (W_lambda) and line-of-sight velocity dispersion (sigma) as a function of D_tran, which together with "down-the-barrel" spectra of the foreground galaxies provide unprecedented maps of neutral hydrogen and ionized metals throughout the CGM of star-forming galaxies at "cosmic noon". A 2D map of Lya absorption depth (vs. line-of-sight velocity and D_tran) for the full ensemble shows a distinct transition near D_tran ~ 80 kpc (close to the virial radius of the average foreground galaxy) where the line-of-sight velocity dispersion reaches a minimum and beyond which the Lya absorption depth flattens. Splitting the sample into subsets based on foreground galaxy properties, we find a strong and monotonic correlation of both W_lambda(C IV) and sigma(C IV) with stellar mass (M_star) at all D_tran including DTB (i.e., D_tran ~ 0 - 250 kpc). Taken together, our results suggest that the kinematics, covering fraction, and spatial extent of CGM gas traced by Lya and (especially) CIV are modulated primarily by halo mass, and that a significant fraction of the CGM gas may be unbound.