Compact groups in theory and practice – I. The spatial properties of compact groups
Compact groups in theory and practice – I. The spatial properties of compact groups
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DOI：
10.1111/j.1365-2966.2008.13328.x
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发表时间：
2008-04
影响因子：
4.8
通讯作者：
A. McConnachie;S. Ellison;D. Patton
中科院分区：
文献类型：
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作者：
A. McConnachie;S. Ellison;D. Patton
我们使用一个基于千禧年模拟的模拟星系表来研究致密星系群的内在空间属性。我们发现，在我们的模拟星表中确认的星系组合中，大约30%是由四个或更多没有入侵者的星系组成的物理致密系统，大约一半是由两个、三个或四个星系与一个或多个入侵者组成的密切关联，其余的星系不是物理致密的(较松散的星系群和物理上不相关的星系的投影)。因此，星系交错的影响是显著的。然而，我们发现真正的致密群比那些有入侵者的更明亮和更孤立；通过将一个群所需的最小表面亮度从μe=26的正规值增加到22 mag arcsec-2，我们可以将没有入侵者的真正紧凑系统的比例从29%提高到75%。在已确定的真正的致密星系群中，超过一半由一个暗物质光环组成，所有成员星系都深深地嵌入其中。在某些情况下，还有其他星系共享相同的光晕(通常质量为∼10 13h-1 M⊙)，但没有被识别为致密群的成员。这意味着紧凑组与组环境相关联，组环境的部分或全部成员都在紧凑组中。对于那些所有星系都在同一个晕中的致密星系群，致密星系群的三维速度色散与暗物质晕的维里速度广泛相关。然而，该群的规模大小--以及该群采样的晕质量的比例--与暗物质晕的性质完全无关。这意味着，在维里平衡的简单假设下，利用观测到的速度色散和致密群的大小得出的质量，给出了对暗物质底层真实质量的错误估计。
We use a mock galaxy catalogue based on the Millennium Run simulation to investigate the intrinsic spatial properties of compact groups of galaxies. We find that approximately 30 per cent of galaxy associations identified in our mock catalogue are physically dense systems of four or more galaxies with no interlopers, approximately half are close associations of two, three or four galaxies with one or more interlopers, and the remainder are not physically dense (projections of looser groups and physically unassociated galaxies). Thus, the effect of interloping galaxies is significant. However, we find that genuine compact groups are preferentially brighter and more isolated than those with interlopers; by increasing the required minimum surface brightness of a group from the canonical value of μ e = 26 to 22 mag arcsec -2 , we can increase the proportion of genuinely compact systems identified with no interlopers from 29 to 75 per cent. Of the genuine compact groups identified, more than half consist of a single dark matter halo with all the member galaxies deeply embedded within it. In some cases, there are other galaxies which share the same halo (typically with mass ∼10 13 h -1 M ⊙ ) but which are not identified as being members of the compact group. This implies that compact groups are associated with group environments, some or all members of which are in the compact group. For those compact groups where all galaxies are in the same halo, the three-dimensional velocity dispersion of the compact group correlates broadly with the virial velocity of the dark matter halo. However, the scale-size of the group - and hence the fraction of the halo mass which the group samples - is completely uncorrelated with the properties of the dark matter halo. This means that masses derived under the simple assumption of virial equilibrium using the observed velocity dispersions and sizes of compact groups give incorrect estimates of the true mass of the underlying dark matter.