THE RELATIONSHIP BETWEEN INTERGALACTIC H I/O VI AND NEARBY ( z < 0.017) GALAXIES

Abstract

We analyze intergalactic HI and OVI absorbers with v<5000 km/s in HST and FUSE spectra of 76 AGNs. The baryons traced by HI/OVI absorption are clearly associated with the extended surroundings of galaxies; for impact parameters <400 kpc they are ~5 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 (rho) and velocity difference (Dv), as well as the fraction of galaxies with an absorber closer than a given rho and Dv. We identify possible "void absorbers" (rho>3 Mpc to the nearest L* galaxy), although at v<2500 km/s all absorbers are within 1.5 Mpc of an L>0.1 L* galaxy. The absorber properties depend on rho, but the relations are not simple correlations. For four absorbers with rho=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 rho<350 kpc the covering factor of Ly-alpha (OVI) around L>0.1 L* galaxies is 100% for field galaxies and 65% for group galaxies; 50% of galaxy groups have associated Ly-alpha. All OVI absorbers occur within 550 kpc of an L>0.25 L* galaxy. The properties of three of 14 OVI absorbers are consistent with photoionization, for five the evidence points to collisional ionization; the others are ambiguous. The fraction of broad Ly-alpha 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 can not be clearly excluded.