Optimal balance of galaxy groups in X-ray property samples

Determine the optimal balance of galaxy groups to include in observational samples used to analyze X-ray properties of galaxy groups, so that the inferred relations and conclusions are not biased by selection effects and large intrinsic scatter revealed by AXES-2MRS and related surveys.

Background

Throughout the paper, the authors show that selection effects and intrinsic diversity in galaxy groups—particularly variations in halo concentration and non-thermal pressure support—lead to large scatter in X-ray scaling relations such as velocity dispersion–X-ray luminosity, velocity dispersion–temperature, and temperature–luminosity. Previous X-ray group catalogues often favored high-concentration, cool-core systems, while AXES-2MRS uncovers many low-concentration groups, expanding the sampled population.

Because different studies report differing slopes and normalizations for key scaling relations, the authors argue that these discrepancies can plausibly stem from how groups are selected for inclusion in X-ray analyses. This motivates an explicit open question about determining the right composition of group samples to ensure representative and unbiased characterization of X-ray properties.