Detection of a Multiphase Intragroup Medium: Results from the COS-IGrM Survey

TL;DR

This study uses the Hubble Space Telescope to observe the intragroup medium in galaxy groups, revealing a patchy, multiphase environment with O VI as a key but not universal tracer of hot gas.

Contribution

First comprehensive UV spectroscopic survey of the intragroup medium, demonstrating its multiphase nature and the limitations of O VI as a universal tracer.

Findings

O VI detected in 8 of 18 groups, indicating patchy hot gas presence.

The IGrM exhibits a wide range of ionization states, confirming its multiphase structure.

O VI correlates with radiatively cooling gas at temperatures around 10^6 K.

Abstract

We present the results of the COS Intragroup Medium (COS-IGrM) Survey that used the Cosmic Origins Spectrograph on the Hubble Space Telescope to observe a sample of 18 UV bright quasars, each probing the intragroup medium (IGrM) of a galaxy group. We detect Ly$\alpha$, C II, N V, Si II, Si III, and O VI in multiple sightlines. The highest ionization species detected in our data is O VI, which was detected in 8 out of 18 quasar sightlines. The wide range of ionization states observed provide evidence that the IGrM is patchy and multiphase. We find that the O VI detections generally align with radiatively cooling gas between $10^{5.8}$ and $10^6$ K. The lack of O VI detections in 10 of the 18 groups illustrates that O VI may not be the ideal tracer of the volume filling component of the IGrM. Instead, it either exists at trace levels in a hot IGrM or is generated in the boundary between the hotter IGrM and cooler gas.