zCOSMOS红移调查：群体环境如何改变全球裁员趋势
The zCOSMOS Redshift Survey: How group environment alters global downsizing trends
摘要：
我们利用zCOSMOS明亮巡天的前约10000个星系及其星系群目录提供的丰富信息来研究星系群环境和星系性质之间复杂的相互作用。经典的指标F_blue（蓝色星系的分数）被证明是一个简单而强大的诊断工具。我们选取不同光度和质量的星系样本，研究了它的变化。使用静止标架B波段选择样本，集团星系人口表现出显着的蓝移的红移增加，但保持较低的F_blue相对于全球和孤立的星系人口。然而，移动到质量选择的样本中，很明显，这种差异主要是由于B波段光度选择所造成的偏见，由较低质量，明亮的蓝色星系的人口驱动，我们错过了更红，同样低质量，对应物。通过将分析集中在窄质量箱上，使得质量分离变得可忽略不计，我们发现仅对于探索的最低质量箱（logMass <= 10.6），颜色的显著残余差异作为环境的函数保持，而这种差异在更高质量时变得可忽略不计。我们的研究结果表明，logMass >= 10.8的红星系已经在z ~ 1的地方，并没有表现出任何强烈的环境依赖性，可能源于所谓的“自然”/内部机制。相比之下，对于较低的星系质量和红移低于z ~ 1，我们观察到的人口的“养育”的红色星系群体的出现：稍微偏离缩小的趋势，其次是全球星系人口，更是如此与宇宙时间。这些星系表现出直接影响星系演化的与星系群相关的长期物理机制的特征。
英文摘要：
We took advantage of the wealth of information provided by the first ~10000 galaxies of the zCOSMOS-bright survey and its group catalogue to study the complex interplay between group environment and galaxy properties. The classical indicator F_blue (fraction of blue galaxies) proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples. Using rest-frame B-band selected samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a lower F_blue with respect both to the global and the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored (logMass <= 10.6) does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses. Our results indicate that red galaxies of logMass >= 10.8 are already in place at z ~ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called 'nature'/internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z ~ 1, we observe the emergence in groups of a population of 'nurture' red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution.
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