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arXiv 0901.4919astro-ph.CO
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在半人马座星系团中寻找大规模UCD

A search for massive UCDs in the Centaurus Galaxy Cluster

S. Mieske, M. Hilker, I. Misgeld, A. Jordan, L. Infante, M. Kissler-Patig

备注：
9 pages, 7 figures, accepted as Research Note for A&A
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摘要：

我们最近开始在半人马座星系团中寻找超紧凑矮星系（UCD）（Mieske et al. 2007），结果发现了27个紧凑的天体，其质量为-12.2<M_V<-10.9 mag.我们的总体调查完整性在120 kpc投影的星系团中心距离内为15-20%。为了更好地限制半人马座最亮UCD的光度分布，我们继续我们的搜索，特别是在M_V<-12等（V_0<21.3等）的制度，大大提高了我们的调查完整性。利用VIMOS在VLT上获得了400个位于半人马座星团中心25'的致密天体的低分辨率光谱，这些天体的质量为19.3<V_0<21.3等（在半人马座距离上为-14<MV <-12等），对应的投影半径约为150 kpc。我们的调查产生完整的区域覆盖范围内~120千秒差距。对于掩模中包含的94%的源，我们成功地测量了红移。由于狭缝分配的不完整性，我们在调查区域的最终完整性为52%。在我们的目标中，我们发现了三个新的UCD，其星等范围为-12.2<M_V<-12等，因此处于我们调查的微弱极限。其中一个被存档的HST WFPC 2成像覆盖，产生r_h <= 8-9 pc的大小估计。在95%的置信度下，我们可以拒绝这样的假设，即在所调查的区域中，有两个以上的大规模UCD，M_V<-12.2 mag，r_eff <=70 pc。因此，我们的调查证实了大规模UCD的极端罕见性。我们发现，半人马座和天炉座的UCD相对于其主机集群的中心的径向分布在2 σ水平一致。

英文摘要：

We recently initiated a search for ultra-compact dwarf galaxies (UCDs) in the Centaurus galaxy cluster (Mieske et al. 2007), resulting in the discovery of 27 compact objects with -12.2<M_V<-10.9 mag. Our overall survey completeness was 15-20% within 120 kpc projected clustercentric distance. In order to better constrain the luminosity distribution of the brightest UCDs in Centaurus, we continue our search by substantially improving our survey completeness specifically in the regime M_V<-12 mag (V_0<21.3 mag). Using VIMOS at the VLT, we obtain low-resolution spectra of 400 compact objects with 19.3<V_0<21.3 mag (-14<M_V<-12 mag at the Centaurus distance) in the central 25' of the Centaurus cluster, which corresponds to a projected radius of ~150 kpc. Our survey yields complete area coverage within ~120 kpc. For 94% of the sources included in the masks we successfully measure a redshift. Due to incompleteness in the slit assignment, our final completeness in the area surveyed is 52%. Among our targets we find three new UCDs in the magnitude range -12.2<M_V<-12 mag, hence at the faint limit of our survey. One of them is covered by archival HST WFPC2 imaging, yielding a size estimate of r_h <= 8-9 pc. At 95% confidence we can reject the hypothesis that in the area surveyed there are more than 2 massive UCDs with M_V<-12.2 mag and r_eff <=70 pc. Our survey hence confirms the extreme rareness of massive UCDs. We find that the radial distributions of Centaurus and Fornax UCDs with respect to their host clusters' centers agree within the 2 sigma level.

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