The relationship between intergalactic H I/O VI and nearby (z < 0.017) galaxies

Abstract

We analyze intergalactic H I and O VI absorbers with v < 5000 kms -1 in Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer spectra of 76 active galactic nuclei. The baryons traced by H I/O VI absorption are clearly associated with the extended surroundings of galaxies; for impact parameters <400 kpc they are 2-4 times more numerous as those inside the galaxies. This large reservoir of matter likely plays a major role in galaxy evolution. We tabulate the fraction of absorbers having a galaxy of a given luminosity within a given impact parameter (ρ) and velocity difference (Δv), as well as the fraction of galaxies with an absorber closer than a given ρ and Δv. We identify possible "void absorbers" (ρ > 3 Mpc to the nearest L * galaxy), although at v < 2500 kms-1 all absorbers are within 1.5 Mpc of an L>0.1L * galaxy. The absorber properties depend on ρ, but the relations are not simple correlations. For four absorbers with ρ = 50-350 kpc from an edge-on galaxy with known orientation of its rotation, we find no clear relation between absorber velocities and the rotation curve of the underlying galaxy. For ρ < 350 kpc, the covering factor of Lyα (O VI) around L>0.1 L * galaxies is 100% (70%) for field galaxies and 65% (10%) for group galaxies; 50% of galaxy groups have associated Lyα. All O VI absorbers occur within 550 kpc of an L>0.25L * galaxy. The properties of three of 14 O VI absorbers are consistent with photoionization, for five the evidence points to collisional ionization; the others are ambiguous. The fraction of broad Lyα lines increases from z = 3 to z = 0 and with decreasing impact parameter, consistent with the idea that gas inside 500 kpc from galaxies is heating up, although alternative explanations cannot be clearly excluded. © 2009. The American Astronomical Society. All rights reserved.