The bimodality of the 10k zCOSMOS-bright galaxies up to z ~ 1: a new statistical and portable classification based on optical galaxy properties
The bimodality of the 10k zCOSMOS-bright galaxies up to z ~ 1: a new statistical and portable classification based on optical galaxy properties
复制标题
高达 z ~ 1 的 10k zCOSMOS 亮星系的双峰性：基于光学星系特性的新统计和便携式分类
DOI：
10.1051/0004-6361/201016130
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发表时间：
2011
影响因子：
6.5
通讯作者：
et al.
中科院分区：
文献类型：
--
作者：
Coppa;Mignoli;Zamorani;...;Tanaka;et al.
目的我们的目标是开发一种新的可靠的统计方法，从大型观测中对星系进行分类。通过使用相同的光谱、光度和形态参数，将该方法与三维分类立方体进行比较，以探讨该方法的可靠性。方法我们对ZCOSMOS红移观测提取的一个星系样本应用了两种不同的分类方法，红移范围为0.5%≲z≲1.3.第一种方法是三种独立分类方案的组合--基于4000°连续谱断裂强度和[O II]发射线的静止帧相当宽度的光谱分类方案，基于观察到的B−z颜色的光度分类方案，以及形态分类方案。第二种方法采用了一种全新的基于统计分析的方法，如主成分分析(PCA)和无监督模糊划分(UFP)聚类法。对红移较小的样本(z≲=0.5)，使用相同的数据集，但用等宽的Hα代替光谱指示器。结果两种方法的比较结果表明，两种方法在早型星系和晚型星系的定义上有很好的一致性。我们的PCA+UFP分类方法是稳健的，灵活的，能够识别两个主要的星系群以及中间的星系群。中间星系群显示了绿谷星系的许多性质，并构成了一个更连贯、更均匀的星系群。所研究的样品的大红移范围使我们能够描述其规模变小的特征：质量为3×1010m⊙的星系主要在0.5岁时从晚期类型向早期类型群过渡，而质量较低的1010m⊙量级的星系则在较晚的时期处于过渡阶段。具有M<；和1010m⊙的星系尚未开始跃迁，而具有非常大质量的星系(M>；和1010m⊙)在Z~1之前大部分已经完成了向早期类型的跃迁。
AimsOur goal is to develop a new and reliable statistical method to classify galaxies from large surveys. We probe the reliability of the method by comparing it with a three-dimensional classification cube, using the same set of spectral, photometric and morphological parameters.MethodsWe applied two different methods of classification to a sample of galaxies extracted from the zCOSMOS redshift survey, in the redshift range 0.5 ≲z≲ 1.3. The first method is a combination of three independent classification schemes – a spectroscopic one based on the strength of the continuum break at 4000 Å and the rest-frame equivalent width of the [O ii] emission line, a photometric one based on the observedB−zcolours, and a morphological one. The second method exploits an entirely new approach based on statistical analyses like principal component analysis (PCA) and unsupervised fuzzy partition (UFP) clustering method. The PCA+UFP method has also been applied to a lower redshift sample (z≲ 0.5), exploiting the same set of data but replacing the spectroscopic indicators with the equivalent width of Hα.ResultsThe comparison between the two methods shows fairly good agreement on the definition on the two main populations, theearly-typeand thelate-typegalaxies. Our PCA+UFP method of classification is robust, flexible and capable of identifying the two main populations of galaxies as well as an intermediate population. The intermediate galaxy population shows many of the properties of “green valley” galaxies, and constitutes a more coherent and homogeneous population. The large redshift range of the studied sample allows us to characterizedownsizing: galaxies with masses of the order of 3 × 1010M⊙are predominantly found in the transition from thelate-typeto theearly-typegroup atz> 0.5, while galaxies with lower masses, of the order of 1010M⊙, are in transition at later epochs. Galaxies withM< 1010M⊙have not yet begun to transition, while galaxies with very large masses (M> 5 × 1010M⊙) have mostly completed their transition to theearly-typeregime beforez~ 1.