标题： JKCS041星系团红移的红色序列确定：z~2.2 显示英文标题

标题： Red sequence determination of the redshift of the cluster of galaxies JKCS041: z~2.2

摘要： 本文旨在稳健地确定星系团JKCS041的红移，并对两个非常高红移星系团中的颜色-星等序列的形成时期施加限制。 新的深度z'-J数据显示出一个清晰的狭窄红色序列，该序列与星系团JKCS041的扩展X射线辐射中心一致，并且同样集中于该区域。 JKCS041的红色序列在z'-J上比zspec=1.62的IRC0218A星系团的红色序列更红0.32+/-0.06 mag，这将JKCS041置于z>>1.62，排除了z<~1.49的可能，后者是最近一篇论文所声称的。 两个红色序列的颜色差异为JKCS041提供了基于红色序列的红移z=2.20+/-0.11，其中不确定性考虑了恒星合成星族模型的不确定性、光度校准的不确定性，以及JKCS041和IRC0218A星系团的红色序列颜色的不确定性。 我们没有观察到两个星系团的红色序列有任何截断的迹象，直至J=23 mag（1.0e+11太阳质量），这表明在这些高红移下，足够丰富和大质量的星系团已经形成了红色序列，并能够加热和保留热气体。 显示英文摘要

摘要： This paper aims at robustly determining the redshift of the cluster of galaxies JKCS041 and at putting constraints on the formation epoch of the color-magnitude sequence in two very high redshift clusters. New deep z'-J data show a clear narrow red sequence that is co-centered with, and similarly concentrated on, the extended X-ray emission of the cluster of galaxies JKCS041. The JKCS041 red sequence is 0.32+/-0.06 mag redder in z'-J than the red sequence of the zspec=1.62 IRC0218A cluster, putting JKCS041 at z>>1.62 and ruling out z<~1.49 the latter claimed by a recent paper. The color difference of the two red sequences gives a red-sequence-based redshift of z=2.20+/-0.11 for JKCS041, where the uncertainty accounts for uncertainties in stellar synthesis population models, in photometric calibration, and in the red sequence color of both JKCS041 and IRC0218A clusters. We do not observe any sign of truncation of the red sequence for both clusters down to J=23 mag (1.0e+11 solar masses), which suggests that it is already in place in clusters rich and massive enough to heat and retain hot gas at these high redshifts.