2014/09/24 by Bruna Vajgel, Christine Jones, Vajgel, Bruna +11
Physics and Astronomy · #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.1409.6822
23 pages, 11 figures
arxiv created 2014/09/24 · arxiv updated 2014/09/25
We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. Our final sample comprises 32 systems at z<1.75, with 14 below z = 0.35. For these 14 systems we estimate velocity dispersions (σgr) and perform a virial analysis to obtain the radii (R200 and R500) and total masses (M200 and M500) for groups with at least five galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (LX). We examine the performance of the group properties σgr, Lopt and LX, as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the LX-M500 relation at approximately M500 = 5×1013 M_\odot (for M500 > 5×1013 M_\odot, M500 ∝ LX0.61±0.02, while for M500 ≤ 5×1013 M_\odot, M500 ∝ LX0.44±0.05). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions and projection effects which reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify ∼1800 groups (LX = 1041-1043 ergs s-1) within a distance of 200 Mpc. Since groups lie in large scale filaments, this group sample will map the large scale structure of the local universe.