标题： z=5.2处靠近射电星系的形成星系团 显示英文标题

标题： Clustering of Star-forming Galaxies Near a Radio Galaxy at z=5.2

摘要： 我们展示了哈勃太空望远镜宽视场相机（HST/ACS）对已知最遥远射电星系TN J0924-2201（红移z=5.2）的观测。 这个射电星系有6个通过光谱确认的发射Lya的伴星系，并且似乎位于一个密度过高的区域。 在i_775和z_850波段，射电星系在一定程度上被解析，显示出与射电轴对齐的连续辐射，这与较低红移射电星系的观测结果相似。 半光子半径和紫外恒星形成率都与在z~4-5时发现的典型Lyman断层星系的值相当。 Lya发射器是次级L*星系，推算出的恒星形成率为1-10倍太阳质量每年。 其中一个Lya发射器仅在Lya波段被探测到。 根据从Lya计算得出的约3倍太阳质量每年的恒星形成率，如果该星系年龄小于约2百万年并且正在形成第一批恒星，则可能解释了连续辐射的缺乏。 使用V_606、i_775和z_850波段的观测来识别与这一结构相关的额外Lyman断层星系。 除了射电星系外，还有22个V断层（z~5）星系，z_850<26.5（5sigma），其中两个也在光谱样本中。 我们将表面密度2/平方角分与从GOODS和UDF平行场中提取的类似选择的V断层星系进行了比较。 基于控制场的单元计数分析，我们发现了非常高的置信度（>99%）的过密证据。 过剩表明V断层对象可能与围绕射电星系形成的星团有关。 显示英文摘要

摘要： We present HST/ACS observations of the most distant radio galaxy known, TN J0924-2201 at z=5.2. This radio galaxy has 6 spectroscopically confirmed Lya emitting companion galaxies, and appears to lie within an overdense region. The radio galaxy is marginally resolved in i_775 and z_850 showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z~4-5. The Lya emitters are sub-L* galaxies, with deduced star formation rates of 1-10 Msun/yr. One of the Lya emitters is only detected in Lya. Based on the star formation rate of ~3 Msun/yr calculated from Lya, the lack of continuum emission could be explained if the galaxy is younger than ~2 Myr and is producing its first stars. Observations in V_606, i_775, and z_850 were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V-break (z~5) galaxies with z_850<26.5 (5sigma), two of which are also in the spectroscopic sample. We compare the surface density of 2/arcmin^2 to that of similarly selected V-dropouts extracted from GOODS and the UDF Parallel fields. We find evidence for an overdensity to very high confidence (>99%), based on a counts-in-cells analysis applied to the control field. The excess is suggestive of the V-break objects being associated with a forming cluster around the radio galaxy.