Non-star-forming molecular gas in the Abell 1367 intra-cluster multiphase orphan cloud

TL;DR

This study reports the first detection of CO emission in an isolated, non-star-forming intra-cluster gas cloud in Abell 1367, revealing complex multi-phase gas interactions and suggesting a ram pressure stripping origin.

Contribution

It provides the first CO detection in an intra-cluster orphan cloud, demonstrating the presence of molecular gas in a non-star-forming, isolated environment within a galaxy cluster.

Findings

Detected about 2.2×10^8 M_sun of H₂ in the cloud.

Molecular gas is offset in velocity from Hα emission by over 100 km/s.

The cloud's molecular component likely accounts for about 10% of its total mass.

Abstract

We report the detection of CO emission in the recently discovered multiphase isolated gas cloud in the nearby galaxy cluster Abell 1367. The cloud is located about 800 kpc in projection from the center of the cluster and at a projected distance of > 80 kpc from any galaxy. It is the first and the only known isolated intra-cluster cloud detected in X-ray, H$\alpha$, and CO emission. We found a total of about $2.2\times 10^8 M_\odot$ of H$_2$ with the IRAM 30-m telescope in two regions, one associated with the peak of H$\alpha$ emission and another with the peak of X-ray emission surrounded by weak H$\alpha$ filaments. The velocity of the molecular gas is offset from the underlying H$\alpha$ emission by > 100 km s$^{-1}$ in the region where the X-ray peaks. The molecular gas may account for about 10% of the total cloud's mass, which is dominated by the hot X-ray component. The previously measured upper limit on the star formation rate in the cloud indicates that the molecular component is in a non-star-forming state, possibly due to a combination of low density of the gas and the observed level of velocity dispersion. The presence of the three gas phases associated with the cloud suggests that gas phase mixing with the surrounding intra-cluster medium is taking place. The possible origin of the orphan cloud is a late evolutionary stage of a ram pressure stripping event. In contrast, the nearby ram pressure stripped galaxy 2MASX J11443212+2006238 is in an early phase of stripping and we detected about $2.4\times 10^9 M_\odot$ of H$_2$ in its main body.