致密星系群SCGG223的ASCA观测

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１１０６ｋｍ／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 ０．５～１０ ｋｅＶ波段 上的光度分别为ｋＴ＝１．４_（－０．４）~（＋．６）： ｋｅＶ和９．８５_（－２．０４）~（６．１１）× １０３６Ｊ 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 ０．５～１０ 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．

ASCA Observation of the Compact Group of Galaxies SCGG 223

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 is inferred that the gravitational mass in SCGG223 may be comparable with that of a typical galaxy cluster, and that the intra-group gas might be extremely hot. In order to investigate these unusual implications, we observed SCGG223 in X-rays with ASCA satellite in Februarys 1999. The gas temperature and the 0.5 ~ 10keV luminosity turned out to be kT = 1.4_(0.4)~(0.6) keV and 9.85_(2.04)~(6.11) x 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-my observations with satellites such as XMM is desirable.