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Yasushi Fukazawa, Kazuo Makishima, Takaya Ohashi, ASCA Compilation of X-Ray Properties of Hot Gas in Elliptical Galaxies and Galaxy Clusters: Two Breaks in the Temperature Dependences, Publications of the Astronomical Society of Japan, Volume 56, Issue 6, 25 December 2004, Pages 965–1009, https://doi.org/10.1093/pasj/56.6.965
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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, |$L_\mathrm{X} \propto (kT)^{\alpha}$|, in the range of |$kT \sim 1.5 \hbox{--} 15 \,\mathrm{keV}$| is |$\alpha = 3.17 \pm 0.15$|, consistent with previous measurements. In the relation, we find two breaks at around ICM temperatures of 1 keV and 4 keV: |$\alpha = 2.34 \pm 0.29$| above 4 keV, |$3.74 \pm 0.32$| in 1.5–5 keV, and |$4.03 \pm 1.07$| below 1.5 keV. Such two breaks are also evident in the temperature and size relation. The steepness in the LT relation at |$kT \gt 4 \,\mathrm{keV} kT \gt 4 \,\mathrm{keV}$| 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 |$M_\mathrm{gas} \propto T^{2.33\pm0.07}$| 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.
