ASCA Compilation of X-Ray Properties of Hot Gas in Elliptical Galaxies and Galaxy Clusters: Two Breaks in the Temperature Dependences

Abstract

Utilizing ASCA archival data of about 300 objects of elliptical galaxies, groups, and clusters of galaxies, we performed systematic measurements of the X-ray properties of hot gas in their systems, and compiled them in this paper. The steepness of the luminosity--temperature (LT) relation, $L_{\rm X}\propto(kT)^{\alpha}$, in the range of $kT=$1.5--15 keV is $\alpha=3.17\pm0.15$, consistent with previous measurements. In the relation, we find two breaks at around ICM temperatures of 1 keV and 4 keV: $\alpha=2.34\pm0.29$ above 4 keV, $3.74\pm0.32$ in 1.5--5 keV, and $4.03\pm1.07$ below 1.5 keV. Such two breaks are also evident in the temperature and size relation. The steepness in the LT relation at $kT>4$ keV is consistent with the scale-relation derived from the CDM model, indicating that the gravitational effect is dominant in richer clusters, while poorer clusters suffer non-gravity effects. The steep LT relation below 1 keV is almost attributed to X-ray faint systems of elliptical galaxies and galaxy groups. We found that the ICM mass within the scaling radius $R_{1500}$ follows the relation of $M_{\rm gas}\propto T^{2.33\pm0.07}$ from X-ray faint galaxies to rich clusters. Therefore, we speculate that even such X-ray faint systems contain a large-scale hot gas, which is too faint to detect.