arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0903.2540astro-ph.CO
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用XMM-Newton和Chandra观测早型星系的引力势和X射线光度

Gravitational potential and X-ray luminosities of early-type galaxies observed with XMM-Newton and Chandra

Ryo Nagino, Kyoko Matsushita

摘要:

我们研究了早型星系中的暗物质含量,并探讨了早型星系的X射线光度是否由周围的引力势决定。利用XMM-Newton和Chandra观测数据,计算了22个早型星系的引力质量分布。16个星系的径向温度分布不变或下降,它们的X射线光度与恒星质量损失的运动学能量输入是一致的。其他6个星系的温度分布随半径的增加而增加,它们的X射线光度明显较高。每个星系的积分质光比在0.5-1 r_e范围内保持不变,并随半径的增大而增大,其中r_e是星系的有效半径。星系中心质光比在K波段的散射较小。在3r_e处,具有平坦或降低温度分布的星系的积分质光比是0.5r_e处的值的两倍,其中恒星质量占主导地位,在6r_e处,这些值增加到0.5r_e处的三倍。这一特征应该反映了早期星系中常见的暗物质和恒星质量分布:在3r_e内,暗物质的质量与恒星质量相似,而在6r_e内,前者比后者大两倍。相比之下,X射线发光星系在外部区域的引力质量比X射线暗淡星系高。我们将这些X射线发光星系描述为具有大势能结构的中心天体;这种势能的存在或不存在是X射线光度中大散射的主要来源。

英文摘要:

We study dark matter content in early-type galaxies and investigate whether X-ray luminosities of early-type galaxies are determined by the surrounding gravitational potential. We derived gravitational mass profiles of 22 early-type galaxies observed with XMM-Newton and Chandra. Sixteen galaxies show constant or decreasing radial temperature profiles, and their X-ray luminosities are consistent with kinematical energy input from stellar mass loss. The temperature profiles of the other 6 galaxies increase with radius, and their X-ray luminosities are significantly higher. The integrated mass-to-light ratio of each galaxy is constant at that of stars within 0.5-1 r_e, and increases with radius, where r_e is the effective radius of a galaxy. The scatter of the central mass-to-light ratio of galaxies was less in K-band light. At 3r_e, the integrated mass-to-light ratios of galaxies with flat or decreasing temperature profiles are twice the value at 0.5r_e, where the stellar mass dominates, and at 6r_e, these increase to three times the value at 0.5r_e. This feature should reflect common dark and stellar mass distributions in early-type galaxies: Within 3r_e, the mass of dark matter is similar to the stellar mass, while within 6r_e, the former is larger than the latter by a factor of two. By contrast, X-ray luminous galaxies have higher gravitational mass in the outer regions than X-ray faint galaxies. We describe these X-ray luminous galaxies as the central objects of large potential structures; the presence or absence of this potential is the main source of the large scatter in the X-ray luminosity.

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