Galaxy Population in a Cluster of Galaxies around the Radio Galaxy 3C 324 at z = 1.2
Galaxy Population in a Cluster of Galaxies around the Radio Galaxy 3C 324 at z = 1.2
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z = 1.2 射电星系 3C 324 周围星系团中的星系群
DOI：
10.1093/pasj/53.6.1139
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发表时间：
2001
影响因子：
2.3
通讯作者：
Naoj Subaru
中科院分区：
文献类型：
--
作者：
F. Nakata;M. Kajisawa;Toru Yamada;T. Kodama;K. Shimasaku;I. Tanaka;M. Doi;H. Furusawa;M. Hamabe;M. Iye;M. Kimura;Y. Komiyama;S. Miyazaki;S. Okamura;M. Ouchi;T. Sasaki;M. Sekiguchi;M. Yagi;N. Y. U. Tokyo;T. Univ.;Naoj;IoA U Tokyo;Jwu;Icrr;Naoj Subaru
我们基于 BV RI K 多波段成像数据讨论了 z =1 .2 处射电星系 3C 324 周围星系的特性。我们对 3C 324 场中的物体应用了光度红移技术，并确定了 35 个物体作为可能的星团成员。我们发现红色和发光成员集中在来自 3C 324 星系的一个半径为 40 �� 的圆（0.33Mpc at z =1.2forΩ0=0.3, λ0=0.7, H0=70kms −1 Mpc −1 宇宙学）包围的小区域中。与本地集群相比，3C 324 集群的大小可能要紧凑得多。我们构建了星团成员的K�带光度函数并拟合了Schechter函数，发现特征星等为K�* AB =2 0.2 ± 0.6。该值与 z <1 簇的纯被动演化的外推一致。我们已经识别出八个明亮的星系，它们形成了红色的颜色-星等序列。序列的斜率与被动演化模型一致，直至 K � AB < 22；我们还发现这些亮红色星系没有明显的年龄变化。然而，相对于被动演化模型，这八个星系中的七个在其余紫外光中表现出明显过量。这可能表明这个高红移星团中的巨大早期型星系在某种程度上仍在形成恒星。我们已经确认了颜色幅度序列在 K � AB ∼ 22 处的截断；在 z ∼ 1.2 的这个星团中可能还不存在微弱的被动演化星系。通过光度红移技术选择的星团成员的整体颜色分布非常广泛。我们根据 Butcher 和 Oemler (1984, AAA 038.160.068) 的定义推导了该星团中蓝色星系的比例，并获得了 fB =0 .39 ±0.28，该值高于 z < 1 星团的值。这表明该星团的恒星形成活动平均高于红移较低的对应星团。
We discuss the properties of galaxies around the radio galaxy 3C 324 at z =1 .2 based on BV RI Kmulti-band imaging data. We have applied a photometric-redshift technique to objects in the 3C 324 field, and identified 35 objects as plausible cluster members. We have found that red and luminous members are concentrated in a small region enclosed by a circle of 40 �� radius (0.33Mpc at z =1.2forΩ0=0.3, λ0=0.7, H0=70kms −1 Mpc −1 cosmology) from the 3C 324 galaxy. The 3C 324 cluster is probably much more compact in size compared with the local clusters. We constructed a K � -band luminosity function of the cluster members and fitted a Schechter function, and found the characteristic magnitude to be K �∗ AB =2 0.2 ± 0.6. This value is consistent with the extrapolation of the pure passive evolution seen for z <1 clusters. We have identified eight bright galaxies which form a red color-magnitude sequence. The slope of the sequence is consistent with the passive evolution model down to K � AB < 22; we also found that there is no clear age variation in these bright red galaxies. However, seven out of these eight galaxies exhibit a significant excess in the rest UV light with respect to the passive evolution model. This may suggest that the massive early-type galaxies in this high-redshift cluster are still forming stars to some extent. We have confirmed a truncation of the color-magnitude sequence at K � AB ∼ 22; faint passively-evolving galaxies may not yet be present in this cluster at z ∼ 1.2. The overall color distribution of the cluster members, selected by the photometric redshift technique, is found to be very broad. We derived the fraction of blue galaxies in this cluster following a definition of Butcher and Oemler (1984, AAA 038.160.068), and obtained fB =0 .39 ±0.28, which is higher than that for z < 1 clusters. This indicates that the star-formation activity of this cluster is, on the average, higher than that of lower redshift counterparts.