Bimodal Galaxies and Bimodality in Globular Cluster Systems
Bimodal Galaxies and Bimodality in Globular Cluster Systems
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双峰星系和球状星团系统中的双峰性
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发表时间：
2005
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通讯作者：
D. Forbes
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作者：
D. Forbes
星系的各种性质在很大的质量范围内并不是连续的，而是在恒星质量为3×10~(10)M☉时显示出显著的跃迁或“双峰”。这些属性包括颜色、恒星数量、X射线发射和质量光比。这一行为被Dekel&Birnboim解释为从热流到冷流的转变。在这里，我们探索球状星团(GC)系统是否也表现出关于这个临界质量尺度的双峰性质。球状星团探测宇宙早期恒星的形成，并在随后的星系合并和吸积中幸存下来。我们使用了来自美国室女座星系团调查(彭及其同事)的新数据，它提供了大约100个处女座早期类型星系的GC系统的均匀样本，覆盖了500个星系质量的范围。他们对GC颜色分布的分类是为了检查一个关键量--单位星系光度的GC数量。在临界质量以下，这个量(称为GC特定频率)的平均值和分布急剧增加。这一增长可能是由于低质量星系中受控制的恒星形成，这反过来又是由于风造成的质量损失以及从热气体吸积流到冷气体吸积流的转变。我们还注意到，在临界质量以上，星系有两个GC亚群(具有蓝色和红色平均颜色)，但在临界质量以下，星系显示出越来越多的单一(蓝色)GC系统。
Various galaxy properties are not continuous over a large range in mass but rather reveal a remarkable transition or "bimodality" at a stellar mass of 3 × 1010 M☉. These properties include colors, stellar populations, X-ray emission, and mass-to-light ratios. This behavior has been interpreted as the transition from hot to cold flows by Dekel & Birnboim. Here we explore whether globular cluster (GC) systems also reveal a bimodal nature with regard to this critical mass scale. Globular clusters probe star formation at early epochs in the universe and survive subsequent galaxy mergers and accretions. We use new data from the ACS Virgo Cluster Survey (Peng and coworkers), which provides a homogeneous sample of the GC systems around 100 Virgo early-type galaxies covering a range of 500 in galaxy mass. Their classification of the GC color distributions is taken to examine a key quantity—the number of GCs per unit galaxy luminosity. Below the critical mass, this quantity (called the GC specific frequency) increases dramatically in its mean value and spread. This increase may be due to regulated star formation in low-mass galaxies, which in turn is due to mass loss via winds and the transition from hot to cold gas accretion flows. We also note that above the critical mass, galaxies possess two GC subpopulations (with blue and red mean colors), but below this mass, galaxies reveal an increasing proportion of single (blue) GC systems.