The Relationship Between Intergalactic HI/OVI and Nearby (z<0.017) Galaxies

TL;DR

This study examines the relationship between intergalactic HI/OVI absorbers and nearby galaxies, revealing their association with galaxy environments and implications for galaxy evolution and gas heating.

Contribution

It provides a detailed analysis of HI/OVI absorbers' distribution around galaxies and introduces new statistical relations between absorbers and galaxy properties.

Findings

Absorbers are more numerous near galaxies than inside galaxies.

OVI absorbers are within 550 kpc of luminous galaxies.

The ionization mechanisms of OVI absorbers vary, with some consistent with photoionization and others with collisional ionization.

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.