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[Abridged] We study the interface between galaxies and the intergalacticmedium by measuring the absorption by neutral hydrogen in the vicinity ofstar-forming galaxies at z~2.4. Our sample consists of 679 rest-frame-UVselected galaxies with spectroscopic redshifts that have impact parameters < 2(proper) Mpc to the line of sight of one of 15 bright, background QSOs. Wepresent the first 2-D maps of the absorption around galaxies, plotting themedian Ly-a pixel optical depth as a function of transverse and line of sight,LOS, separation from galaxies. The median optical depth, and hence the mediandensity of atomic hydrogen, drops by more than an order of magnitude around 100kpc, which is similar to the virial radius of the halos thought to host thegalaxies. The median remains enhanced (>3 sigma level) out to at least 2.8 Mpc(i.e. > 9 comoving Mpc). Within 100 (200) kpc, and over \pm 165 km/s, thecovering fraction of gas with Ly-a optical depth greater than unity is100(+0)(-32)% (86(+14)(-18)%). Absorbers with tau(Ly-a)> 0.1 are typicallycloser to galaxies than random. The mean galaxy overdensity around absorbersincreases with the optical depth and also as the length scale over which thegalaxy overdensity is evaluated is decreased. Absorbers with tau(Ly-a)~1 residein regions where the galaxy number density is close to the cosmic mean onscales > 0.25 Mpc. We detect two types of redshift space anisotropies. Onscales < 200 km/s, or < 1 Mpc, the absorption is stronger along the LOS than inthe transverse direction. This "finger of God" effect may be partly due toredshift errors, but is probably dominated by gas motions within or very closeto the halos. On the other hand, on scales of 1.4 - 2.0 Mpc the absorption iscompressed along the LOS (>3 sigma significance), which we attribute tolarge-scale infall (i.e. the Kaiser effect).

Neutral hydrogen optical depth near star-forming galaxies at z~2.4 in the Keck Baryonic Structure Survey