星系的紫外-光学色-色-星等关系
A universal ultraviolet-optical colour-colour-magnitude relation of galaxies
摘要：
虽然星系的光学颜色星等图允许我们选择红色序列天体，但在没有光谱或高分辨率图像等额外观测数据的情况下，它既不能用于星系分类，也不能用于识别红移未知的蓝色星系。我们发现，添加近紫外线的颜色的光学CMD揭示了紧密的关系，在三维的颜色-颜色-幅度空间顺利地继续从“蓝色云”的“红色序列”。我们发现225，000个低红移（Z<0.27）星系中有98%遵循光滑表面g-r=F（M，NUV-r），标准差为0.03-0.07等，使其成为已知最紧密的星系光度关系。形态类型和综合NUV-r颜色之间有很强的相关性。罕见的星系类，如E+A或潮汐剥离系统成为离群值，占据不同的区域在3D参数空间。利用具有不同SFH的星系的恒星星族模型，我们表明：（a）（NUV-r，g-r）分布是由具有常数和指数衰减的SFR的天体在不同的特征时间尺度上形成的：（b）指数衰减模型的颜色演化沿关系式发展，表明其在红移0.9之前的弱演化;（c）具有截断的超星系的跃迁相位偏离关系式很短，从而解释了E+A星系的稀少性。这种关系可以被用来作为一个强大的星系分类工具时，形态仍然没有解决。其数学结果是由3个宽波段测光点的测光红移估计。这种方法比大多数现有的应用于多色数据集的光度红移技术更好。因此，该关系可以作为一种有效的选择技术，在中等红移（0.3<Z<0.8）的星系使用光学成像调查。
英文摘要：
Although the optical colour-magnitude diagram of galaxies allows one to select red sequence objects, neither can it be used for galaxy classification without additional observational data such as spectra or high-resolution images, nor to identify blue galaxies at unknown redshifts. We show that adding the near ultraviolet colour to the optical CMD reveals a tight relation in the three-dimensional colour-colour-magnitude space smoothly continuing from the "blue cloud" to the "red sequence". We found that 98 per cent of 225,000 low-redshift (Z<0.27) galaxies follow a smooth surface g-r=F(M,NUV-r) with a standard deviation of 0.03-0.07 mag making it the tightest known galaxy photometric relation. There is a strong correlation between morphological types and integrated NUV-r colours. Rare galaxy classes such as E+A or tidally stripped systems become outliers that occupy distinct regions in the 3D parameter space. Using stellar population models for galaxies with different SFHs, we show that (a) the (NUV-r, g-r) distribution is formed by objects having constant and exponentially declining SFR with different characteristic timescales; (b) colour evolution for exponentially declining models goes along the relation suggesting its weak evolution up-to a redshift of 0.9; (c) galaxies with truncated SFHs have very short transition phase offset from the relation thus explaining the rareness of E+A galaxies. This relation can be used as a powerful galaxy classification tool when morphology remains unresolved. Its mathematical consequence is the photometric redshift estimates from 3 broad-band photometric points. This approach works better than most existing photometric redshift techniques applied to multi-colour datasets. Therefore, the relation can be used as an efficient selection technique for galaxies at intermediate redshifts (0.3<Z<0.8) using optical imaging surveys.
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