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arXiv 1502.01256astro-ph.GA
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晕集合时间的观测代用指标及其与星系性质的关系

An observational proxy of halo assembly time and its correlation with galaxy properties

Seunghwan Lim, Houjun Mo, Huiyuan Wang, Xiaohu Yang

备注：
13 pages, 13 figures, accepted for publication in MNRAS
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摘要：

我们发现，中央星系的恒星质量与其宿主晕的质量之比，$f_c \equiv M_{*,c}/M_{\rm h}$，可以被用来作为一个可观察的代理晕组装时间，即具有较高的$f_c$星系团组装他们的质量早。使用Yang等人的SDSS组，我们研究了$f_c$如何与星系的性质，如颜色、恒星形成率、金属丰度、球盘比和大小相关。在具有$f_c>0.02$的星系群中，具有一定恒星质量的中央星系，随着$f_c$的增加，颜色会变得更红，在恒星形成过程中会变得更冷，体积会变得更小，并且会变得更突出。颜色和恒星形成的趋势似乎在$f_c<0.02$发生逆转，反映了一种缩小效应，即大质量晕中的星系形成恒星的时间更早，尽管宿主晕本身组装的时间更晚（较低的$f_c$）。在椭圆星系的大小中没有看到这样的逆转，这表明它们的组装比它们的恒星形成更接近于晕的生长。当$f_c$增加时，在给定晕质量的星系群中，具有给定恒星质量的卫星星系的颜色往往更红，在恒星形成时更淬灭，尺寸也更小。对于一个给定的恒星质量，卫星也往往比中心小。低质量群体的趋势更强。对于质量大于$\sim 10^{13}{\rm M}_\odot$的星系群，在颜色和恒星形成方面可以看到一个微弱的反向趋势。所观察到的恒星形成的趋势是定性再现的经验模型的基础上晕年龄丰度匹配，但不是由半分析模型在这里测试。

英文摘要：

We show that the ratio between the stellar mass of central galaxy and the mass of its host halo, $f_c \equiv M_{*,c}/M_{\rm h}$, can be used as an observable proxy of halo assembly time, in that galaxy groups with higher $f_c$ assembled their masses earlier. Using SDSS groups of Yang et al., we study how $f_c$ correlates with galaxy properties such as color, star formation rate, metallicity, bulge to disk ratio, and size. Central galaxies of a given stellar mass in groups with $f_c>0.02$ tend to be redder in color, more quenched in star formation, smaller in size, and more bulge dominated, as $f_c$ increases. The trends in color and star formation appear to reverse at $f_c<0.02$, reflecting a down-sizing effect that galaxies in massive halos formed their stars earlier although the host halos themselves assembled later (lower $f_c$). No such reversal is seen in the size of elliptical galaxies, suggesting that their assembly follows halo growth more closely than their star formation. Satellite galaxies of a given stellar mass in groups of a given halo mass tend to be redder in color, more quenched in star formation and smaller in size as $f_c$ increases. For a given stellar mass, satellites also tend to be smaller than centrals. The trends are stronger for lower mass groups. For groups more massive than $\sim 10^{13}{\rm M}_\odot$, a weak reversed trend is seen in color and star formation. The observed trends in star formation are qualitatively reproduced by an empirical model based on halo age abundance matching, but not by a semi-analytical model tested here.

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