The Connection between Galaxies and Intergalactic Absorption Lines at Redshift 2 ≲ z ≲ 3

Abstract

Absorption-line spectroscopy of 23 background QSOs and numerous background galaxies has let us measure the spatial distribution of metals and neutral hydrogen around 1044 UV-selected galaxies at redshifts 1.8 ≲ z ≲ 3.3. The typical galaxy is surrounded to radii r ~ 40 proper kpc by gas that has a large velocity spread (Δv > 260 km s-1) and produces very strong absorption lines (N ≫ 1014 cm-2) in the spectra of background objects. These absorption lines are almost as strong as those produced by a typical galaxy's own interstellar gas. Absorption with an average column density of N ≃ 1014 cm-2 extends out to ~80 kpc, a radius large enough to imply that most strong intergalactic C IV absorption is associated with star-forming galaxies like those in our sample. Our measurement of the galaxy-C IV spatial correlation function shows that even the weakest detectable C IV systems are found in the same regions as galaxies; we find that the cross-correlation length increases with C IV column density and is similar to the galaxy autocorrelation length (r0 ~ 4 h-1 Mpc) for N ≳ 1012.5 cm-2. Distortions in the redshift-space galaxy-C IV correlation function on small scales may imply that some of the C IV systems have large peculiar velocities. Four of the five detected O VI absorption systems in our sample lie within 400 proper kpc of a known galaxy. Strong Lyα absorption is produced by the intergalactic gas within 1 h-1 comoving Mpc of most galaxies, but for a significant minority (~) the absorption is weak or absent. This is not observed in smooth-particle hydrodynamic simulations that omit the effects of "feedback" from galaxy formation. We were unable to identify any statistically significant differences in age, dust reddening, environment, or kinematics between galaxies with weak nearby H I absorption and the rest, although galaxies with weak absorption may have higher star formation rates. Galaxies near intergalactic C IV systems appear to reside in relatively dense environments and to have distinctive spectral energy distributions that are characterized by blue colors and young ages.