The DEEP Groth Strip Survey X: Number Density and Luminosity Function of Field E/S0 Galaxies at z < 1

We present the luminosity function and color-redshift relation of a magnitude-limited sample of 145 mostly red field E/S0 galaxies at z 1.5. Constructing a luminosity function of the full sample of 145 E/S0s, we find that there is about 1.1--1.9 magnitude brightening in rest-frame B band luminosity back to z = 0.8 from z=0, consistent with other studies. Together with the red colors, this brightening favors models in which the bulk of stars in red field E/S0s formed before z_{for} > 1.5 and have been evolving rather quiescently with few large starbursts since then. Evolution in the number density of field E/S0 galaxies is harder to measure, and uncertainties in the raw counts and their ratio to local samples might amount to as much as a factor of two. Within that uncertainty, the number density of red E/S0s to z = 0.8 seems relatively static, being comparable to or perhaps moderately less than that of local E/S0s depending on the assumed cosmology. A doubling of E/S0 number density since z = 1 can be ruled out with high confidence (97%) if \Omega_{m}=1. Taken together, our results are consistent with the hypothesis that the majority of luminous field E/S0s were already in place by z = 1, that the bulk of their stars were already fairly old, and that their number density has not changed by large amounts since then.

我们给出了在红移$z\approx1.5$处145个大多为红色的场椭圆星系/透镜状星系（E/S0）的一个星等限制样本的光度函数以及颜色 - 红移关系。构建145个E/S0星系完整样本的光度函数后，我们发现从$z = 0$到$z = 0.8$，在静止帧B波段光度大约增亮了1.1 - 1.9个星等，这与其他研究结果一致。 结合其红色，这种增亮现象支持这样的模型：红色场E/S0星系中的大部分恒星在$z_{for}>1.5$之前形成，并且从那时起一直相当平静地演化，很少有大的星暴。 场E/S0星系的数密度演化更难测量，原始计数及其与本地样本的比率的不确定性可能高达两倍。 在该不确定性范围内，到$z = 0.8$的红色E/S0星系的数密度似乎相对稳定，与本地E/S0星系的数密度相当，或者可能略低于本地的，这取决于所假定的宇宙学模型。如果$\Omega_{m}=1$，则可以非常有把握（97%）地排除自$z = 1$以来E/S0数密度翻倍的情况。 综上所述，我们的结果与以下假设一致：大多数发光的场E/S0星系在$z = 1$时已经存在，它们的大部分恒星已经相当古老，并且从那时起它们的数密度没有发生很大变化。