The specific frequencies of ultra-compact dwarf galaxies
The specific frequencies of ultra-compact dwarf galaxies
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DOI：
10.1051/0004-6361/201117634
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发表时间：
2011-12
影响因子：
6.5
通讯作者：
S. Mieske;M. Hilker;I. Misgeld
中科院分区：
文献类型：
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作者：
S. Mieske;M. Hilker;I. Misgeld
上下文超致密矮星系（UCD）的一个形成通道是大质量星星团，另一个主要的场景是潮汐转变的矮星系。目标。我们的目标是量化的特定频率的UCD在一系列的环境和相关的频率的星星集群和潜在的祖矮星系。UCD的频率与球状星团光度函数（GCLF）的亮尾一致吗？方法.我们提出了UCD的特定频率的定义，S N，UCD = NUCD 10 0.4（MV，host-MV，0）cw。参数MV，0是定义的零点，选择它使得UCD的比频与球状星团的比频相同，S N，GC，i如果UCD遵循GCLF的简单外推。考虑到UCD是MV < −10.25 mag（质量大于102 × 106 M ²）的紧凑恒星系统，它是MV，0 = −20 mag。参数cw是考虑GCLF宽度σ对宿主星系光度依赖性的修正项。我们应用我们的定义S N，UCD光谱UCD搜索结果在天炉座，长蛇座，半人马座星系团，两个希克森紧凑组，和本地组。这包括一个大型数据库，其中包含Fornax中180个已确认的UCD。结果我们发现，UCD的特定频率与GC的频率非常匹配，在10 - 50%以内。天炉座、长蛇座、半人马座和本星系群四个环境的S值为1.00 ± 0.44，具有SN、GC值。这种良好的匹配也适用于天炉座和天炉座团内空间中的单个巨星系。在不同环境中导出的UCD特定频率的误差范围则意味着不超过50%的UCD形成于矮星系。我们发现，这样的情况将需要90%的原始矮星在星系团中心（<100千秒差距）已被剥夺了他们的恒星。结论.我们的结论是，UCD的数量计数与它们作为GC群体的亮尾完全一致。从统计学的角度来看，不需要调用额外的地层通道。
Context. One formation channel discussed for ultra-compact dwarf galaxies (UCDs) is that of massive star clusters, and the other main scenario is that of tidally transformed dwarf galaxies. Aims. We aim at quantifying the specific frequency of UCDs in a range of environments and at relating this to the frequency of star clusters and potential progenitor dwarf galaxies. Are the frequencies of UCDs consistent with being the bright tail of the globular cluster luminosity function (GCLF)? Methods. We propose a definition for the specific frequency of UCDs, S N,UCD = NUCD10 0.4(MV,host −MV,0) cw. The parameter MV,0 is the zero point of the definition, chosen such that the specific frequency of UCDs is the same as those of globular clusters, S N,GC ,i f UCDs follow a simple extrapolation of the GCLF. Considering UCDs as compact stellar systems with MV < −10.25 mag (mass above ∼2 × 10 6 M� ), it is MV,0 = −20 mag. The parameter cw is a correction term to take the dependence of the GCLF width σ on the host galaxy luminosity into account. We apply our definition of S N,UCD to results of spectroscopic UCD searches in the Fornax, Hydra, and Centaurus galaxy clusters, two Hickson compact groups, and the Local Group. This includes a large database of 180 confirmed UCDs in Fornax. Results. We find that the specific frequencies derived for UCDs match those of GCs very well, to within 10‐50%. The ratio S is 1.00 ± 0.44 for the four environments Fornax, Hydra, Centaurus, and Local Group, which have S N,GC values. This good match also holds for individual giant galaxies in Fornax and in the Fornax intracluster-space. The error ranges of the derived UCD specific frequencies in the various environments then imply that not more than ∼50% of UCDs were formed from dwarf galaxies. We show that such a scenario would require 90% of primordial dwarfs in galaxy cluster centers (<100 kpc) to have been stripped of their stars. Conclusions. We conclude that the number counts of UCDs are fully consistent with them being the bright tail of the GC population. From a statistical point of view there is no need to invoke an additional formation channel.