# The Warm Circum-Galactic Medium: 10^5-6 K Gas Associated with a Single Galaxy Halo or with an Entire Group of Galaxies?

## TL;DR

This study investigates the origin of warm, 10^5-6 K gas detected via OVI absorption near galaxies and groups, emphasizing the need for high-quality data and comprehensive galaxy surveys to determine whether such gas is associated with individual galaxies or entire groups.

## Contribution

The paper presents a case study of OVI absorption near a galaxy group, highlighting the importance of high-S/N COS data and deep galaxy surveys to distinguish between galaxy and group origins of warm gas.

## Key findings

- Detected OVI absorption near a galaxy group at z=0.11326.
- Analysis favors association of warm gas with a single galaxy rather than the entire group.
- Emphasizes the need for high-quality data and extensive galaxy surveys for accurate interpretation.

## Abstract

In preparation for a Hubble Space Telescope (HST) observing project using the Cosmic Origins Spectrograph (COS), the positions of all AGN targets having high-S/N far-UV G130M spectra were cross-correlated with a large catalog of low-redshift galaxy groups homogeneously selected from the spectroscopic sample of the Sloan Digital Sky Survey (SDSS). Searching for targets behind only those groups at z = 0.1-0.2 (which places the OVI doublet in the wavelength region of peak COS sensitivity) we identified only one potential S/N = 15-20 target, FBQS 1010+3003. An OVI-only absorber was found in its G130M spectrum at z = 0.11326, close to the redshift of a foreground small group of luminous galaxies at z = 0.11685. Because there is no associated Lyalpha absorption, any characterization of this absorber is necessarily minimal; however, the OVI detection likely traces "warm" gas in collisional ionization equilibrium at T ~ 300,000 K. While this discovery is consistent with being interface gas between cooler, photoionized clouds and a hotter intra-group medium, it could also be warm, interface gas associated with the circum-galactic medium (CGM) of the single closest galaxy. In this case a detailed analysis of the galaxy distribution (complete to 0.2 L*) strongly favors the individual galaxy association. This analysis highlights the necessity of both high-S/N > 20 COS data and a deep galaxy redshift survey of the region in order to test more rigorously the association of OVI-absorbing gas with a galaxy group. A Cycle 23 HST/COS program currently is targeting 10 UV-bright AGN behind 12 low-redshift galaxy groups to test the warm, group gas hypothesis.