致密星系群SCGG223的ASCA观测

摘要

光学观测表明，致密星系群SCGG 223中成员星系的速度弥散高达1106 km/s，并且整个星系群处于平衡状态. 星系群的数值模拟也显示，SCGG 223是维里化的. 这些光学波段上的研究结果暗示，SCGG 223可能具有星系团量级的大引力质量, 其星系际气体则很可能处在极高温的状态. 为了证实这些推测, 作者在1999年2月利用ASCA卫星对SCGG 223进行了X射线观测. 通过光谱分析，获得了它的气体温度和0.510 keV波段上的光度分别为kT=1.4+0.6-0.4 keV和9.85+6.11-2.041036 J s-1. 与光学观测所作出的预计相反，这些数值显示SCGG 223是一个正常的低温星系群. 由于SCGG 223在0.510 keV波段上很暗，无法从ASCA获得的X射线表面亮度分布推算其总引力质量, 因此，尚不能直接判断它的质量是否真的像光学维里质量那样大.%Optical observations of the compact group of galaxies SCGG223 show that the velocity dispersion in it is as high as 1106 km s-1, and the group itself seems to be relaxed. Numerical simulations also suggest that SCGG223 is virialized. Therefore, it isinferred that the gravitational mass in SCGG223 may be comparable with that ofa typical galaxy cluster, and that the intra-group gas might be extremely hot. In order to investigate these unusual implications, we observed SCGG223in X-rays with ASCA satellite in February, 1999. Thegas temperature and the 0.5 10 keV luminosity turned out to bekT=1.4+0.6-0.4 keVand9.85+6.11-2.04 1036 J s-1,which show that SCGG223 is a usual galaxy group. Due to the lack of enough photon counts, we are not able to make an X-ray spectroscopical imaging to deduce the radial distribution of the gravitating mass to compare with that of the optical virial mass. Thus, for a more complete understanding of SCGG223, further X-ray observations with satellites such as XMM is desirable.