卫星生态学：环境依赖的终结
Satellite Ecology: The Dearth of Environment Dependence
摘要：
利用Yang et al.（2007）的Sloan Digital Sky Survey（SDSS）星系群星表，我们研究了卫星星系的平均颜色和平均浓度随（i）恒星质量、（ii）星系群质量和（iii）星系群中心半径的变化。我们发现，卫星星系的颜色和浓度（几乎）完全取决于它们的恒星质量。特别是，在固定的恒星质量，卫星星系的平均颜色和浓度是独立的晕质量或晕中心半径。我们发现明确的证据，卫星星系的质量分离晕的所有质量，并认为这解释了为什么卫星在较小的晕中心半径有点红，有点更集中。此外，卫星星系的颜色和浓度对晕质量的依赖性很弱，这仅仅反映了这样一个事实，即平均而言，更大质量的晕拥有更多质量的卫星。将这些结果与卫星星系平均比相同恒星质量的中心星系更红和更集中的事实相结合，出现了以下图片：星系变得更红，一旦它们落入更大的晕中（即，一旦它们成为卫星星系）。这是对环境依赖的一种明显表现。然而，没有迹象表明转变的幅度（或其时间尺度）取决于环境;星系在成为卫星时会经历转变，但它是否成为小（银河系大小）晕的卫星或大质量星团并不重要。我们讨论的影响，这种“缺乏”的环境依赖的物理过程负责改造卫星星系。
英文摘要：
Using the Sloan Digital Sky Survey (SDSS) galaxy group catalogue of Yang et al. (2007), we study the average colour and average concentration of satellite galaxies as function of (i) their stellar mass, (ii) their group mass, and (iii) their group-centric radius. We find that the colours and concentrations of satellite galaxies are (almost) completely determined by their stellar mass. In particular, at fixed stellar mass, the average colours and concentrations of satellite galaxies are independent of either halo mass or halo-centric radius. We find clear evidence for mass segregation of satellite galaxies in haloes of all masses, and argue that this explains why satellites at smaller halo-centric radii are somewhat redder and somewhat more concentrated. In addition, the weak colour and concentration dependence of satellite galaxies on halo mass is simply a reflection of the fact that more massive haloes host, on average, more massive satellites. Combining these results with the fact that satellite galaxies are, on average, redder and somewhat more concentrated than central galaxies of the same stellar mass, the following picture emerges: galaxies become redder and somewhat more concentrated once they fall into a bigger halo (i.e., once they become a satellite galaxy). This is a clear manifestation of environment dependence. However, there is no indication that the magnitude of the transformation (or its timescale) depends on environment; a galaxy undergoes a transition when it becomes a satellite, but it does not matter whether it becomes a satellite of a small (Milky Way sized) halo, or of a massive cluster. We discuss the implication of this `dearth' of environment dependence for the physical processes responsible for transforming satellite galaxies.
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