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arXiv 0903.0215astro-ph.GAastro-ph.CO
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Scl-dE1 GC1:低光度矮椭圆星系中的扩展球状星团

Scl-dE1 GC1: An Extended Globular Cluster in a Low-Luminosity Dwarf Elliptical Galaxy

G. S. Da Costa, E. K. Grebel, H. Jerjen, M. Rejkuba, M. E. Sharina

摘要:

本文报道了利用哈勃空间望远镜ACS图像在玉夫座矮椭圆星系Scl-dE 1(Sc22)中发现的一个扩展的球状星团,记作Scl-dE 1 GC 1。在色星等图中,dE距离红巨星分支顶端的I星等为4.3 +/- 0.25 Mpc。在这个距离上,Scl-dE 1 GC 1的半光半径约为22 pc,是已知最大的星团之一,特别是与矮星系有关的球状星团。Scl-dE 1 GC 1的绝对星等为Mv = -6.7,在光度不确定性的范围内,星团的恒星星族似乎与dE无法区分。我们认为在矮星系中可能存在两种球状星团形成模式,一种是半光半径为3 pc的“正常”模式,另一种是半光半径为~10 pc或更大的“扩展”模式。

英文摘要:

We report the discovery from Hubble Space Telescope ACS images of an extended globular cluster, denoted by Scl-dE1 GC1, in the Sculptor Group dwarf Elliptical galaxy Scl-dE1 (Sc22). The distance of the dE is determined as 4.3 +/- 0.25 Mpc from the I magnitude of the tip of the red giant branch in the color-magnitude diagram. At this distance the half-light radius of Scl-dE1 GC1 is ~22 pc, placing it among the largest clusters known, particularly for globular clusters associated with dwarf galaxies. The absolute magnitude of Scl-dE1 GC1 is Mv = -6.7 and, to within the photometric uncertainties of the data, the cluster stellar population appears indistinguishable from that of the dE. We suggest that there may be two modes of globular cluster formation in dwarf galaxies, a "normal" mode with half-light radii of typically 3 pc, and an "extended" mode with half-light radii of ~10 pc or more.

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