Core Structure of Intracluster Gas: Isothermal Hydrostatic Equilibrium

• Published in: Publications of the Astronomical Society of Japan 2005-06, Vol.57 (3), p.419-427
• Main Authors: Akahori, Takuya, Masai, Kuniaki
• Format: Article
• Language: English
• ISSN: 0004-6264; 2053-051X
• DOI: 10.1093/pasj/57.3.419

We investigated the core structure of intracluster hot gas based on the so-called $\beta$ -model. We found that the virial temperature, $T_{\mathrm{vir}}$ , of a cluster may be represented better by $\beta T_{\mathrm{X}}$ than $T_{\mathrm{X}}$ , where $\beta$ is a parameter obtained from the X-ray surface brightness, and $T_{\mathrm{X}}$ is the emission-weighted mean temperature of the gas. For 121 clusters observed by ROSAT and ASCA, the luminosity-temperature relation, $L_{\mathrm{X}} \hbox{--} \beta T_{\mathrm{X}}$ , is found to be less steep than $L_{\mathrm{X}} \hbox{--} T_{\mathrm{X}}$ . The clusters can be classified into large and small core groups, and the latter exhibits no significant correlation between the core and virial radii. We examined the properties of the small core clusters, and found that they have a shorter cooling time than the Hubble time, while no significant correlation was found with the presence of cD galaxies or asymmetry in the surface brightness. We carried out hydrodynamical calculations to simulate the $\beta$ -model and confirmed the above results: $T_{\mathrm{vir}} \simeq \beta T$ for the gas temperature, $T$ , and the gas core formed due to a central cD galaxy is too small to account for the cores of the smaller core clusters.