Exploring the Diversity of Groups at 0.1<z<0.8 with X-ray and Optically Selected Samples

TL;DR

This study compares galaxy groups selected via X-ray and optical methods at redshifts 0.12 to 0.79, analyzing their properties, scaling relations, and the effects of different radial cuts on group characterization.

Contribution

It provides a detailed comparison of X-ray and optically selected galaxy groups, introducing an X-ray based radius for more accurate virialization assessment and analyzing the impact of selection methods on group properties.

Findings

X-ray based r200 reduces scatter in scaling relations.

X-ray and optical selected groups show similar Lx-sigma and Mstellar-Lx relations.

X-ray underluminous groups have lower stellar mass fractions and less contribution from the most massive galaxy.

Abstract

We present the global group properties of two samples of galaxy groups containing 39 high quality X-ray selected systems and 38 optically (spectroscopically) selected systems in coincident spatial regions at 0.12<z<0.79. Only nine optical systems are associable with X-ray systems. We discuss the confusion inherent in the matching of both galaxies to extended X-ray emission and of X-ray emission to already identified optical systems. Extensive spectroscopy has been obtained and the resultant redshift catalog and group membership are provided here. X-ray, dynamical, and total stellar masses of the groups are also derived and presented. We explore the effects of applying three different kinds of radial cut to our systems: a constant cut of 1 Mpc and two r200 cuts, one based on the velocity dispersion of the system and the other on the X-ray emission. We find that an X-ray based r200 results in less scatter in scaling relations and less dynamical complexity as evidenced by results of the Anderson-Darling and Dressler-Schectman tests, indicating that this radius tends to isolate the virialized part of the system. The constant and velocity dispersion based cuts can overestimate membership and can work to inflate velocity dispersion and dynamical and stellar mass. We find Lx-sigma and Mstellar-Lx scaling relations for X-ray and optically selected systems are not dissimilar. The mean fraction of mass found in stars for our systems is approximately 0.014 with a logarithmic standard deviation of 0.398 dex. We also define and investigate a sample of groups which are X-ray underluminous given the total group stellar mass. For these systems the fraction of stellar mass contributed by the most massive galaxy is typically lower than that found for the total population of groups implying that there may be less IGM contributed from the most massive member in these systems. (Abridged)