The Morphology of Distant Cluster Galaxies. II. HST Observations of Four Rich Clusters at z ≃ 0.4
The Morphology of Distant Cluster Galaxies. II. HST Observations of Four Rich Clusters at z ≃ 0.4
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遥远星系团的形态 II. 四个丰富星系团的 HST 观测
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发表时间：
1997
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通讯作者：
H. Butcher
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作者：
Augustus Oemler, Jr.;A. Dressler;H. Butcher
本文介绍了哈勃空间望远镜（HST）WF/PC和WFPC 2对红移z ~ 0.4的四个富星系团CL 1447+2619、CL 0939+4713、CL 0024+1654和阿贝尔370的观测结果。广泛的地面观测表明，所有这些星系都有大量的蓝色星系、恒星形成星系和（在某些情况下）恒星爆发星系。我们发现这些星系团中的星系群是近似正常的，因为大多数星系可以容纳在z = 0哈勃序列中，并且具有哈勃类型所预期的星系团内的亮度，颜色和分布。然而，在每一个星系团的环境中，星系群中晚型星系的比例都比今天在类似环境中发现的要高。重新计算以前的地面和HST观测，我们发现了一个非常大的部分扰动系统。其中许多的出现暗示着合并和潮汐相互作用的物体，但一些困难表明，新描述的“星系骚扰”过程可能是一个更可能的解释。这些物体显然是负责大多数的恒星暴光谱检测到的地面观测的集群。然而，它们不能解释大部分的蓝色星系。这种扰动星系的比例随星系团的不同而变化，与蓝色星系和螺旋星系的数量一致。所有这些变化都与星系团的结构和密度有很好的相关性，但与星系团的丰富度无关。对“正常”螺旋的仔细检查表明，相当一部分有非常不正常的星星形成模式：星星形成的环比双臂螺旋更常见。这种类型的星系在附近的族群中非常罕见，但在HST观测高红移场族群时也发现过。我们推测，这些形式可能是集群环境的产物，或者可能只是代表在这个红移观察到的盘演化的早期阶段的规范。
We present Hubble Space Telescope (HST) WF/PC and WFPC2 observations of four rich clusters of galaxies at redshifts z ~ 0.4: CL 1447+2619, CL 0939+4713, CL 0024+1654, and Abell 370. Extensive ground-based observations have shown that all have substantial populations of blue, star-forming, and (in some cases) starbursting galaxies. We find the galaxy populations in these clusters to be approximately normal, in that most galaxies can be accommodated in the z = 0 Hubble sequence and have the luminosities, colors, and distributions within the clusters that are expected for their Hubble types. However, in every cluster environment the galaxy populations contain a uniformly higher proportion of late-type galaxies than is found in similar environments today. Confirming previous ground-based and HST observations, we find a remarkably large fraction of disturbed systems. The appearance of many of these is suggestive of merging and tidally interacting objects, but several difficulties with this suggest that the newly described process of “galaxy harassment” may be a more likely explanation. These objects are clearly responsible for the majority of the starburst spectra detected in ground-based observations of the clusters. They cannot, however, account for most of the large population of blue galaxies. The fraction of such disturbed galaxies varies from cluster to cluster in concert with the number of blue and of spiral galaxies. All these variations are well correlated with the structure and density of the clusters, but not with cluster richness. Close examination of the population of “normal” spirals shows that a significant fraction have very abnormal patterns of star formation: Rings of star formation are much more common than two-armed spirals. Galaxies of this type are very rare in nearby populations but also have been found in HST observations of high-redshift field populations. We speculate that these forms might be products of the cluster environment or may simply represent the norm for the earlier stage of disk evolution observed at this redshift.