Quantifying the Bimodal Color-Magnitude Distribution of Galaxies
Quantifying the Bimodal Color-Magnitude Distribution of Galaxies
复制标题
DOI：
10.1086/380092
复制
发表时间：
2003-09
期刊：
影响因子：
--
通讯作者：
I. Baldry;K. Glazebrook;J. Brinkmann;Ž. Ivezić;R. Lupton;R. Nichol;A. Szalay
中科院分区：
文献类型：
--
作者：
I. Baldry;K. Glazebrook;J. Brinkmann;Ž. Ivezić;R. Lupton;R. Nichol;A. Szalay
我们分析了来自斯隆数字巡天（2400平方度，0.004 < z < 0.08， -23.5 < Mr < -15.5）的一个低红移星系样本在颜色与绝对星等（u - r与Mr）方面的二元分布。我们通过对按绝对星等区间划分的颜色函数拟合双高斯分布，追踪了从亮星系到暗星系分布的双峰性。在不使用任何形态学截断的情况下，获得了红色和蓝色分布（早型和晚型，主要是场星系）的颜色 - 星等（CM）关系。相反，该分析基于颜色呈正态高斯分布的假设。我们发现CM关系可以很好地用一条直线加上一个双曲正切函数来拟合。这两种关系都可以用一个较浅的CM趋势（斜率约为 -0.04， -0.05）加上在大约2个星等范围内平均星系性质的一个更陡的转变来描述。在将光度转换为恒星质量后，转变的中点（红色和蓝色分布分别为Mr = -19.8和 -20.8）出现在约2×10¹⁰太阳质量处。分别获得了两种分布的光度函数。与蓝色分布（α≈ -1.3，取决于参数化）相比，红色分布具有更亮的特征星等和更浅的暗端斜率（M* = -21.5，α = -0.8）。这些大致被转换为星系恒星质量函数。对于质量大于约3×10¹⁰太阳质量的情况，红色分布星系每星等的数密度更高。利用一个简单的合并模型，我们表明这两个函数之间的差异与红色分布由主要的星系合并形成是一致的。
We analyze the bivariate distribution, in color versus absolute magnitude (u-r vs. Mr), of a low-redshift sample of galaxies from the Sloan Digital Sky Survey (2400 deg2, 0.004 < z < 0.08, -23.5 < Mr < -15.5). We trace the bimodality of the distribution from luminous to faint galaxies by fitting double Gaussians to the color functions separated in absolute magnitude bins. Color-magnitude (CM) relations are obtained for red and blue distributions (early- and late-type, predominantly field, galaxies) without using any cut in morphology. Instead, the analysis is based on the assumption of normal Gaussian distributions in color. We find that the CM relations are well fitted by a straight line plus a tanh function. Both relations can be described by a shallow CM trend (slopes of about -0.04, -0.05) plus a steeper transition in the average galaxy properties over about 2 mag. The midpoints of the transitions (Mr = -19.8 and -20.8 for the red and blue distributions, respectively) occur around 2 × 1010 ℳ☉ after converting luminosities to stellar mass. Separate luminosity functions are obtained for the two distributions. The red distribution has a more luminous characteristic magnitude and a shallower faint-end slope (M* = -21.5, α = -0.8) compared to the blue distribution (α ≈ -1.3, depending on the parameterization). These are approximately converted to galaxy stellar mass functions. The red distribution galaxies have a higher number density per magnitude for masses greater than about 3 × 1010 ℳ☉. Using a simple merger model, we show that the differences between the two functions are consistent with the red distribution being formed from major galaxy mergers.