极红和大质量星系在极高红移时的年龄
The age of extremely red and massive galaxies at very high redshift
摘要：
目标。我们提出了一个确定的内在颜色和年龄的星系在非常高的红移，特别是老星系（OG）内的极红天体（EROS）。迄今为止，ERO的定义仅限于z<2.5的天体，然而，这里考虑具有相同性质但红移更高（z>2.5）的天体。因此，我们将这些天体称为甚高红移EROS（Z-EROS）。方法.我们分析了在XMM-LSS场中选择的63，550个星系。为了获得合理规模的地球观测目标样本，必须考虑进行大面积的调查。我们确定的目标范围内的0.77平方度的光学中红外数据可从SUBARU，UKIDSS和斯皮策。我们根据颜色选择Z-ERO，然后只选择OG。我们的创新之一是将基于滤波器I和K的ERO选择的传统方法适应于更高的红移。使用我们的方法，我们确定了20个对象，满足所需的条件是Z-ERO/OG在红移2.5<z<3.8在光度红移的误差的一些保守的约束。对于这些物体中的每一个，我们计算相应的静止颜色（B-V），并通过将该颜色与合成模型进行比较来估计它们的平均恒星质量和年龄。结果我们选择的星系具有高恒星质量（~10^{11} M_sun）并且年龄大于1 Gyr，因此它们的恒星星族形成于z>~4.7处。在包括了之前论文中分析的z<2.5的星系之后，我们发现形成时代明显取决于观测到的红移和恒星质量：恒星质量越高，宇宙形成时的年龄就越低。这一结果似乎与Lambda-CDM模型相冲突，该模型声称最大质量的星系在较低质量之后形成。
英文摘要：
Aims. We present a determination of the intrinsic colors and ages of galaxies at very high redshift, in particular old galaxies (OGs) within extremely red objects (EROs). To date, the definition of EROs has been restricted to objects with z<2.5, however, here consider objects with the same properties but shifted to higher redshifts (z>2.5). We therefore, refer to these objects as very high-redshift EROs (Z-EROS, herein). Methods. We analyze 63,550 galaxies selected in the XMM-LSS field. To obtain a reasonably sized sample of EROs, it is essential to consider a very wide area surveys. We identify targets within an area of 0.77 square degrees for which optical to mid-infrared data are available from SUBARU, UKIDSS, and Spitzer. We select Z-EROs based on their colors, and then perform a selection of only OGs. One of our novel innovations is to adapt the traditional method of EROs selection based on the filters I and K, to higher redshifts. Using our method, we identify 20 objects that satisfy the conditions required to be Z-EROs/OGs at redshifts 2.5<z<3.8 within some conservative constraints of errors in the photometric redshifts. For each of these objects, we calculate the corresponding color at rest (B-V), and estimate their average stellar mass and age by comparing this color with a synthesis model. Results. Our selected galaxies have high stellar masses (~10^{11} M_sun) and are older than 1 Gyr, hence their stellar populations were formed at z>~4.7. After including additional galaxies with z<2.5 analyzed in a previous paper, we find that the formation epoch depends significantly on the observed redshift and stellar mass: the higher the stellar mass, the lower the age of the Universe at which it was formed. This result appears to conflict with Lambda-CDM models that claim that the most massive galaxies formed after lower mass.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
