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arXiv 0910.3209astro-ph.CO
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第一代室女星系团矮椭圆星系？

The First Generation of Virgo Cluster Dwarf Elliptical Galaxies?

T. Lisker, J. Janz, G. Hensler, S. Kim, S. -C. Rey, S. Weinmann, C. Mastropietro, O. Hielscher, S. Paudel, R. Kotulla

备注：
Accepted by ApJL, 6 pages, 4 figures. The astro-ph version includes the galaxy images as Fig. A1 for illustration purposes
发表信息：
Astrophys.J.706:L124-L128,2009
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摘要：

在光的问题是否大多数早期型矮（dE）星系团形成的晚型祖先的下降和改造，我们寻找这样的下降历史的印记，在最古老的，最集中的dE子类的室女星系团：有核dE，没有迹象表明磁盘或中央残留恒星形成。我们选择在一个（投影）区域的中心椭圆星系，并细分他们的视线速度为快速移动和缓慢移动的。这些子样本的形状有很大的不同：快速的dE是相对平坦的物体，而慢速的dE几乎是圆形的。同样，当将中心dEs按其投影轴比细分为平坦和圆形时，它们的视线速度分布显著不同：平坦dEs具有宽的，可能是双峰分布，而圆形dEs显示窄的单峰。我们的结论是，圆的dEs可能是圆形的轨道，而平坦的dEs仍然是在更偏心或径向轨道典型的人口下降。在这幅图中，圆形的dE可能已经在星团中居住了很长时间，甚至可能是一个星团诞生的物种，这解释了它们近乎圆形的轨道。因此，它们将是第一代室女星系团dE。它们的形状可能是由重复的潮汐相互作用的动力加热造成的。通过恒星星族测量和模拟星系团的研究进行进一步的调查是可取的，以获得关于其起源的明确结论。

英文摘要：

In the light of the question whether most early-type dwarf (dE) galaxies in clusters formed through infall and transformation of late-type progenitors, we search for an imprint of such an infall history in the oldest, most centrally concentrated dE subclass of the Virgo cluster: the nucleated dEs that show no signatures of disks or central residual star formation. We select dEs in a (projected) region around the central elliptical galaxies, and subdivide them by their line-of-sight velocity into fast-moving and slow-moving ones. These subsamples turn out to have significantly different shapes: while the fast dEs are relatively flat objects, the slow dEs are nearly round. Likewise, when subdividing the central dEs by their projected axial ratio into flat and round ones, their distributions of line-of-sight velocities differ significantly: the flat dEs have a broad, possibly two-peaked distribution, whereas the round dEs show a narrow single peak. We conclude that the round dEs probably are on circularized orbits, while the flat dEs are still on more eccentric or radial orbits typical for an infalling population. In this picture, the round dEs would have resided in the cluster already for a long time, or would even be a cluster-born species, explaining their nearly circular orbits. They would thus be the first generation of Virgo cluster dEs. Their shape could be caused by dynamical heating through repeated tidal interactions. Further investigations through stellar population measurements and studies of simulated galaxy clusters would be desirable to obtain definite conclusions on their origin.

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