早型系统中色矢量的起源及其在高z处的紧性
The Origin of Color Gradients in Early-Type Systems and Their Compactness at High-z
摘要：
在这封信中，我们提出了平均光学+近红外颜色梯度估计的5080早型星系（ETG）的grizYJHK波段的斯隆数字巡天（SDSS）加上UKIRT红外深空巡天（UKIDSS）。颜色梯度被估计为ETG中径向颜色分布的对数斜率。在如此大的样本量下，我们以前所未有的精度研究了平均颜色梯度随波段的变化。我们发现：（i）颜色梯度主要是由于，平均而言，约-0.4dex每十年的星系半径的金属丰度变化;（ii）一个小的，但显着的，积极的年龄梯度是目前，平均而言，在ETG，与内部恒星星族是稍微年轻，约0.1dex每径向十年，比外部的。此外，我们表明，在ETG的存在下，一个积极的平均年龄梯度，在本研究中发现，意味着他们的有效半径要小，在高z，与观察一致。
英文摘要：
In this Letter, we present mean optical+NIR color gradient estimates for 5080 early-type galaxies (ETGs) in the grizYJHK wavebands of the Sloan Digital Sky Survey (SDSS) plus UKIRT Infrared Deep Sky Survey (UKIDSS). The color gradient is estimated as the logarithmic slope of the radial color profile in ETGs. With such a large sample size, we study the variation of the mean color gradient as a function of waveband with unprecedented accuracy. We find that (i) color gradients are mainly due, on average, to a metallicity variation of about -0.4dex per decade in galaxy radius; and (ii) a small, but significant, positive age gradient is present, on average, in ETGs, with the inner stellar population being slightly younger, by ~0.1dex per radial decade, than the outer one. Also, we show that the presence of a positive mean age gradient in ETGs, as found in the present study, implies their effective radius to be smaller at high z, consistent with observations.
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