从z=0-2双色序列中静止星系的探测
Detection of quiescent galaxies in a bicolor sequence from z=0-2
摘要：
我们利用一种新的静止坐标系颜色选择技术，利用纯光度数据研究了静止星系和恒星形成星系在z~2范围内的种群特性。从UKIDSS超深巡天数据Release 1中，匹配的光学和中红外测光分别从斯巴鲁XMM深巡天和斯皮策广域红外河外巡天，我们构建了一个K-选择星系表和计算光度红移。除去恒星、z_phot解不确定的天体、观测区域不好或不完整的天体，以及无法得到可靠的静止坐标系颜色的天体，剩下30108个K<22.4（AB）和z<2.5的星系。这个样本中的星系在静止坐标系的U-V与V-J色空间中占据两个不同的群体：一群红色的静止星系（类似于红色序列）和一条从蓝色延伸到红色U-V色的恒星形成星系的轨道。这种双峰行为被视为高达z~2。由于测量误差和被动演化的结合，色-色图不适合区分z>2的星系双峰性，但我们表明MIPS 24 μ m的数据表明，即使在这些较高的红移下，也存在大量的静止星系。在z=1-2时，样本中最明亮的天体大致平均分为恒星形成星系和静止星系，而在较低的红移时，大多数最明亮的星系都是静止的。此外，处于这些红移的静止星系比那些活跃形成的恒星更强烈地聚集在一起，这表明具有早期淬火恒星形成的星系可能占据更多质量的暗物质晕。这表明恒星形成的结束与晕质量相关的机制有关，也许是由晕质量相关的机制引起的。
英文摘要：
We investigate the properties of quiescent and star-forming galaxy populations to z~2 with purely photometric data, employing a novel rest-frame color selection technique. From the UKIDSS Ultra-Deep Survey Data Release 1, with matched optical and mid-IR photometry taken from the Subaru XMM Deep Survey and Spitzer Wide-Area Infrared Extragalactic Survey respectively, we construct a K-selected galaxy catalog and calculate photometric redshifts. Excluding stars, objects with uncertain z_phot solutions, those that fall in bad or incomplete survey regions, and those for which reliable rest-frame colors could not be derived, 30108 galaxies with K<22.4 (AB) and z<2.5 remain. The galaxies in this sample are found to occupy two distinct populations in the rest-frame U-V vs. V-J color space: a clump of red, quiescent galaxies (analogous to the red sequence) and a track of star-forming galaxies extending from blue to red U-V colors. This bimodal behavior is seen up to z~2. Due to a combination of measurement errors and passive evolution, the color-color diagram is not suitable to distinguish the galaxy bimodality at z>2 for this sample, but we show that MIPS 24um data suggest that a significant population of quiescent galaxies exists even at these higher redshifts. At z=1-2, the most luminous objects in the sample are divided roughly equally between star-forming and quiescent galaxies, while at lower redshifts most of the brightest galaxies are quiescent. Moreover, quiescent galaxies at these redshifts are clustered more strongly than those actively forming stars, indicating that galaxies with early-quenched star formation may occupy more massive host dark matter halos. This suggests that the end of star formation is associated with, and perhaps brought about by, a mechanism related to halo mass.
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