Scaling Properties of a Complete X-ray Selected Galaxy Group Sample

TL;DR

This study analyzes X-ray selected galaxy groups to refine scaling relations between observable properties and mass, accounting for selection effects and non-gravitational physics, with implications for cosmological surveys.

Contribution

It provides the first robust, bias-corrected scaling relations for galaxy groups and compares observational data with hydrodynamical simulations to understand feedback effects.

Findings

The corrected L-M relation is steeper than observed and previous estimates.

Feedback processes significantly influence galaxy group formation.

Gas mass fraction varies by nearly a factor of two between groups and clusters.

Abstract

Upcoming X-ray surveys like eROSITA require precise calibration between X-ray observables and mass down to the low mass regime to set tight constraints on the fundamental cosmological parameters. Since an individual mass measurement is only possible for a relatively small number of objects it is crucial to have robust and well understood scaling relations that relate the total mass to easily observable quantities. The main goal of this work is to constrain the galaxy group scaling relations corrected for selection effects, and to quantify the influence of non-gravitational physics at the low-mass regime. We analyzed XMM-Newton observations for a complete sample of galaxy groups selected from the ROSAT All-Sky Survey and we compared the derived scaling properties with a galaxy cluster sample. To investigate the role played by the different non-gravitational processes we then compared the observational data with the predictions of hydrodynamical simulations. After applying the correction for selection effects (e.g. Malmquist bias) the L-M relation is steeper than the observed one. Its slope is also steeper than the value obtained by using the more massive systems of the HIFLUGCS sample. This behaviour can be explained by a gradual change of the true L-M relation which should be taken into account when converting the observational parameters into masses. The other observed scaling relations (not corrected for selection biases) do not show any break although the comparison with the simulations suggests that feedback processes play an important role in the formation and evolution of galaxy groups. Thanks to our master sample of 82 objects spanning two order of magnitude in mass we tightly constrain the dependence of the gas mass fraction on the total mass, finding almost a factor of two difference between groups and clusters.