The Galaxy Environment of OviAbsorption Systems

Abstract

We combine a FUSE sample of O VI absorbers (z < 0.15) with a database of 1.07 million galaxy redshifts to explore the relationship between absorbers and galaxy environments. All 37 absorbers with N OVI ≥ 10 13.2 cm −2 lie within 800 h −1 70 kpc of the nearest galaxy, with no compelling evidence for O VI absorbers in voids. The O VI absorbers often appear to be associated with environments of individual galaxies. Gas with 10 ± 5% solar metallicity (O VI and C III) has a median spread in distance of 350-500 h −1 70 kpc around L ⋆ galaxies and 200-270 h −1 70 kpc around 0.1L ⋆ galaxies (ranges reflect uncertain metallicities of gas undetected in Lyα absorption). In order to match the O VI line frequency, (dN /dz) ≈ 20 for N OVI ≥ 10 13.2 cm −2 , galaxies with L ≤ 0.1L ⋆ must contribute to the cross section. Lyman-α absorbers with N HI ≥ 10 13.2 cm −2 cover ∼ 50% of the surface area of typical galaxy filaments. Two-thirds of these show O VI and/or C III absorption, corresponding to a 33-50% covering factor at 0.1Z ⊙ and suggesting that metals are spread to a maximum distance of 800 h −1 70 kpc, within typical galaxy supercluster filaments. Approximately 50% of the O VI absorbers have associated Lyα line pairs with separations (∆v) Lyα = 50 − 200 km s −1. These pairs could represent shocks at the speeds necessary to create copious O VI, located within 100 h −1 70 kpc of the nearest galaxy and accounting for much of the two-point correlation function of low-z Lyα forest absorbers.

The Warm Circumgalactic Medium: 105−6 K Gas Associated with a Single Galaxy Halo or with an Entire Group of Galaxies?

“…Absorbers at larger impact parameters often (∼ 1/3 of cases) have ambiguous galaxy associations or are plausibly associated with entire small groups of galaxies (see also Paper 2). Additionally, low-ion metal-bearing absorbers are found at ρ R vir excepting H I+O VI-only absorbers which are found out to impact parameters of nearly 1 Mpc from the nearest bright galaxy (Stocke et al 2006(Stocke et al , 2013Keeney et al 2017), many of which likely are associated with entire groups of galaxies (Paper 2). But there is no indication that the virial radius (R vir , or R sub in the group context) is a firm boundary for the CGM of an individual galaxy so we use it here only as an indicator that the absorber might or might not be associated with the CGM of an individual galaxy.…”

“…This leaves broad, shallow O VI and Lyα UV absorption lines as the best current method for discovering hot gas in galaxy groups. Statistical studies (Stocke et al 2006;Finn et al 2016) on the extent to which O VI absorbers are found away from galaxies suggest that metal enriched gas is spread ≈ 1 Mpc from its source. This distance is about the diameter of a small galaxy group.…”

THE GAS–GALAXY CONNECTION ATzabs= 0.35: O VI AND H I ABSORPTION TOWARD J 0943+0531

“…O vi can be found in a diverse range of environments, from galaxies to groups, filaments, and the IGM (Savage et al 1998;Tripp & Savage 2000;Tripp et al 2001;Prochaska et al 2006Prochaska et al , 2011Stocke et al 2006;Lehner et al 2009). Several studies have shown a correlation with galaxies on large spatial scales (e.g., Stocke et al 2006;Prochaska et al 2011), and there appears to be a correlation with emission-linedominated galaxies (Chen & Mulchaey 2009).…”

“…O vi can be found in a diverse range of environments, from galaxies to groups, filaments, and the IGM (Savage et al 1998;Tripp & Savage 2000;Tripp et al 2001;Prochaska et al 2006Prochaska et al , 2011Stocke et al 2006;Lehner et al 2009). Several studies have shown a correlation with galaxies on large spatial scales (e.g., Stocke et al 2006;Prochaska et al 2011), and there appears to be a correlation with emission-linedominated galaxies (Chen & Mulchaey 2009). Several recent statistical surveys (Tripp et al 2008;Danforth & Shull 2008;Thom & Chen 2008a) have studied O vi in the low-z IGM with the Space Telescope Imaging Spectrograph (STIS), but while some of the gas can be shown to be cool (Tripp et al 2006;Thom & Chen 2008b), much of it is multi-phase gas or its ionization state cannot be determined (e.g., Tripp et al 2008;Thom & Chen 2008b).…”

Dim Baryons in the Cosmic Web

“…There is often a Lyman-α absorber a small projected separation from a bright galaxy, but not every absorber has a bright galaxy nearby (Bowen, Pettini, & Blades 2002). The environment of the high ionization WHIM absorbers is beginning to be explored (Stocke et al 2006).…”