AXES-2MRS: A new all-sky catalogue of extended X-ray galaxy groups

Abstract

We present a new all-sky catalogue of X-ray detected groups (AXES-2MRS), based on the identification of large X-ray sources found in the ROSAT All-Sky Survey (RASS) with the Two Micron Redshift Survey (2MRS) Bayesian Group Catalogue. We study the basic properties of these galaxy groups to gain insights into the effect of different group selections on the properties. In addition to X-ray luminosity coming from shallow survey data of RASS, we have obtained detailed X-ray properties of the groups by matching the AXES-2MRS catalogue to archival X-ray observations by XMM-Newton and complemented this by adding the published XMM-Newton results on galaxy clusters in our catalogue. We analyse temperature and density to the lowest overdensity accessible by the data, obtaining hydrostatic mass estimates and comparing them to the velocity dispersions of the groups. We find a large spread in the central mass to virial mass ratios for galaxy groups in the XMM-Newton subsample. This can either indicate large non-thermal pressure of galaxy groups affecting our X-ray mass measurements, or the effect of a diversity of halo concentrations on X-ray properties of galaxy groups. Previous catalogues, based on detecting the peak of the X-ray emission preferentially sample the high-concentration groups, while our new catalogue includes many low-concentration groups. Abridged.