z~2处的新生红序列
The Nascent Red Sequence at z~2
摘要：
我们提出了新的约束早期型星系的颜色-星等关系（CMR）的基础上的星系原星团在z=2.16的深近红外成像的演变使用NICMOS船上的哈勃太空望远镜。这个区域包含了光谱学证实的莱曼α和H α发射星系的空间超密度，它们围绕着强大的射电星系MRC 1138-262。使用这些NICMOS数据，我们确定了一个显着的表面超密度（= 6.2倍）的红色J-H星系的颜色星等图（与深NICMOS图像从HDF-N和UDF相比）。这些红色序列星系的光学近红外颜色表明，在大多数红色星系中存在正在进行的尘埃遮蔽的恒星形成或最近形成的（<~ 1.5 Gyr）恒星星族。我们测量的斜率和内在散射的CMR为三个不同的红色星系样本选择了一个广泛的颜色切割，并使用光度红移有和没有限制的休息帧光学形态。在这三种情况下，静止坐标系的$U-B$斜率和固有的颜色散射都大大高于相应的值较低的红移星系团。这些结果表明，虽然一些相对静止的星系确实存在于这个原星系团的大部分星系人口，因此颜色-星等关系仍在形成的过程中，正如预期的那样。
英文摘要：
We present new constraints on the evolution of the early-type galaxy color-magnitude relation (CMR) based on deep near-infrared imaging of a galaxy protocluster at z=2.16 obtained using NICMOS on-board the Hubble Space Telescope. This field contains a spectroscopically confirmed space-overdensity of Lyman-alpha and H-alpha emitting galaxies which surrounds the powerful radio galaxy MRC 1138-262. Using these NICMOS data we identify a significant surface-overdensity (= 6.2x) of red J-H galaxies in the color-magnitude diagram (when compared with deep NICMOS imaging from the HDF-N and UDF). The optical-NIR colors of these prospective red-sequence galaxies indicate the presence of on-going dust-obscured star-formation or recently formed (<~ 1.5 Gyr)stellar populations in a majority of the red galaxies. We measure the slope and intrinsic scatter of the CMR for three different red galaxy samples selected by a wide color cut, and using photometric redshifts both with and without restrictions on rest-frame optical morphology. In all three cases both the rest-frame $U-B$ slope and intrinsic color scatter are considerably higher than corresponding values for lower redshift galaxy clusters. These results suggest that while some relatively quiescent galaxies do exist in this protocluster both the majority of the galaxy population and hence the color-magnitude relation are still in the process of forming, as expected.
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