Dark Matter and Gas Concentrations in the NGC 4532/DDO 137 System
Dark Matter and Gas Concentrations in the NGC 4532/DDO 137 System
复制标题
NGC 4532/DDO 137 系统中的暗物质和气体浓度
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
Bryan M. Connell
中科院分区：
文献类型：
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作者：
G. L. Hoffman;N. Lu;E. Salpeter;Bryan M. Connell
NGC 4532和DDO 137是室室座星系团边缘的一对Sm星系，它们的H I合成图被用来确定每个星系的旋转曲线，并解决了在早期阿雷西博系统研究中发现的弥散H I扩展包络中嵌入的三种不同的H I浓度的结构和运动学。三种浓度的氢离子质量似乎不足以使它们自引力；然而，它们的H I质量和动力质量与室女座星系团中微弱的I星系非常相似。每个云的峰值H I柱密度接近恒星形成阈值，但B和R中的CCD图像没有显示恒星或恒星形成的痕迹。如果该系统受到引力约束并处于维里平衡状态，我们发现它的总质量是单个星系和星云最外层的H I等高线内质量的10倍。根据VLA的测绘，总H I的37%位于单个星系的边界之外；28%不能归因于星系或离散的浓度。解释速度场和大量弥漫气体的一种可能的方法是假设DDO 137、气体浓度和其他明显的潮汐特征是由于气体落入该星系群的暗物质势内的团块，并且在相互作用之前，该星系群由一个不规则星系（NGC 4532）和一个像H I 1225+01这样的大型恒星稀少的H I云组成。
H I synthesis mapping of NGC 4532 and DDO 137, a pair of Sm galaxies on the edge of the Virgo Cluster, is used to determine rotation curves for each of the galaxies and to resolve the structure and kinematics of three distinct H I concentrations embedded in an extended envelope of diffuse H I discovered in earlier Arecibo studies of the system. The H I masses of the three concentrations do not appear to be sufficient for them to be self-gravitating; however, their H I masses and dynamical masses are very similar to those of faint Im galaxies in the Virgo Cluster. The peak H I column density of each of the clouds is close to the star formation threshold, but CCD images in B and R reveal no trace of stars or star formation. If the system is gravitationally bound and in virial equilibrium, we find its total mass to be 10 times that within the outermost H I contours of the individual galaxies and clouds. Thirty-seven percent of the total H I lies outside the boundaries of the individual galaxies as determined by the VLA mapping; 28% cannot be ascribed to either galaxy or to the discrete concentrations. One possible way to account for the velocity field and the large quantity of diffuse gas is to assume that DDO 137, the gas concentrations, and other apparent tidal features are due to gas infall into clumps within the dark matter potential of the group, and that prior to the interaction the group consisted of an irregular galaxy (NGC 4532) and a large, star-poor H I cloud like H I 1225+01.