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

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, LX ∝ (kT ), in the range of kT =1.5–15 keV is α= 3.17± 0.15, consistent with previous measurements. In the relation, we find two breaks at around ICM temperatures of 1 keV and 4 keV: α= 2.34± 0.29 above 4 keV, 3.74± 0.32 in 1.5–5 keV, and 4.03±1.07 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 R1500 follows the relation of Mgas ∝ T 2.33±0.07 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.