ACCESS IV：尘埃S0s星团中恒星形成的猝灭
ACCESS IV: The quenching of star formation in a cluster population of dusty S0s
摘要：
本文利用Spitzer/MIPS 24和70 μ m全景成像技术对沙普利超星系团核心（SSC）中165个70 μ m探测到的星系的中红外（MIR）颜色进行了分析。虽然大部分星系显示出典型的本地恒星形成星系的f70/f24颜色，但我们确定了23个70微米过量星系的重要子群，其MIR颜色（f70/f24>25）要红得多，并且不能被任何标准模型红外SED再现。这些星系被发现强烈地集中在组成SSC的五个星系团的核心，并且在局部场星系中也很少见，这证实了它们是一种特定的星系团现象。它们的光谱和缺乏显着的紫外线辐射意味着很少或没有正在进行的恒星形成，而适合他们的全色SED需要远红外辐射主要来自于一般星际辐射场加热的弥漫尘埃成分，而不是正在进行的恒星形成。这些70微米以上的星系大多数被确认为~L* S 0，具有平滑的轮廓。我们发现，几乎每个星系团在恒星形成淬火过程中已经是一个S 0或Sa，而我们没有发现任何被动星系的Sb类或以后。因此，形成被动的早期型星系在集群核心必须涉及到后期型螺旋到Sa/S 0的形态转换之前，也许通过预处理或集群潮汐场的影响，在随后淬火的恒星形成一旦透镜遇到密集的环境的集群核心。在许多S 0星系团的情况下，恒星形成猝灭阶段的特征是超过70微米的辐射，表明冷尘埃含量的下降速度比恒星形成的速度慢。
英文摘要：
We present an analysis of the mid-infrared (MIR) colours of 165 70um-detected galaxies in the Shapley supercluster core (SSC) at z=0.048 using panoramic Spitzer/MIPS 24 and 70um imaging. While the bulk of galaxies show f70/f24 colours typical of local star-forming galaxies, we identify a significant sub-population of 23 70micron-excess galaxies, whose MIR colours (f70/f24>25) are much redder and cannot be reproduced by any of the standard model infrared SEDs. These galaxies are found to be strongly concentrated towards the cores of the five clusters that make up the SSC, and also appear rare among local field galaxies, confirming them as a cluster-specific phenomenon. Their optical spectra and lack of significant UV emission imply little or no ongoing star formation, while fits to their panchromatic SEDs require the far-IR emission to come mostly from a diffuse dust component heated by the general interstellar radiation field rather than ongoing star formation. Most of these 70micron-excess galaxies are identified as ~L* S0s with smooth profiles. We find that almost every cluster galaxy in the process of star-formation quenching is already either an S0 or Sa, while we find no passive galaxies of class Sb or later. Hence the formation of passive early-type galaxies in cluster cores must involve the prior morphological transformation of late-type spirals into Sa/S0s, perhaps via pre-processing or the impact of cluster tidal fields, before a subsequent quenching of star formation once the lenticular encounters the dense environment of the cluster core. In the cases of many cluster S0s, this phase of star-formation quenching is characterised by an excess of 70um emission, indicating that the cold dust content is declining at a slower rate than star formation.
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