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arXiv 1104.2595astro-ph.CO
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0.4 < z < 2.2时恒星形成星系和静止星系的数密度和质量密度

The number density and mass density of star-forming and quiescent galaxies at 0.4 < z < 2.2

Gabriel B. Brammer, Katherine E. Whitaker, Pieter G. van Dokkum, Danilo Marchesini, Marijn Franx, Mariska Kriek, Ivo Labbe, Kyoung-Soo Lee, Adam Muzzin, Ryan F.… 展开作者

Gabriel B. Brammer, Katherine E. Whitaker, Pieter G. van Dokkum, Danilo Marchesini, Marijn Franx, Mariska Kriek, Ivo Labbe, Kyoung-Soo Lee, Adam Muzzin, Ryan F. Quadri, Gregory Rudnick, Rik Williams

摘要:

我们使用NEWFIRM中波段巡天研究了双峰星系群的形成,该巡天提供了约27,000个K<22.8,0.4 < z < 2.2的星系的优异红移和良好采样的光谱能量分布。我们首先表明,恒星形成的星系和静止的星系可以在整个红移范围内用双色标准来分离。然后,我们研究了静止和恒星形成星系的数密度和质量密度的演化,将COMBO-17,DEEP 2和其他调查的结果扩展到z=2.2。从z=2到现在,M > 3 10^11太阳质量的静止星系的质量密度增加了约10倍,而在同一时期,恒星形成星系的质量密度是平坦的或减少的。由于质量函数的指数尾很陡,单个静止星系的质量适度增长2倍,可以解释大约一半的M>10^11太阳质量的强烈密度演化。大质量静止星系的密度演化的其余部分可能是由于大质量恒星形成群体的转变(例如淬火),这一结论与我们观察到的恒星形成星系本身的密度演化一致,这是平坦的或随着宇宙时间而减少。适度的质量增长并不能解释质量较小的静止星系(~10^10.5太阳质量)的演化,它们的数量密度也显示出类似的急剧增加。因此,质量较小的静止星系是由恒星形成群体中的星系不断转化而成的

英文摘要:

We study the build-up of the bimodal galaxy population using the NEWFIRM Medium-Band Survey, which provides excellent redshifts and well-sampled spectral energy distributions of ~27,000 galaxies with K<22.8 at 0.4 < z < 2.2. We first show that star-forming galaxies and quiescent galaxies can be robustly separated with a two-color criterion over this entire redshift range. We then study the evolution of the number density and mass density of quiescent and star-forming galaxies, extending the results of the COMBO-17, DEEP2, and other surveys to z=2.2. The mass density of quiescent galaxies with M > 3 10^11 solar masses increases by a factor of ~10 from z=2 to the present day, whereas the mass density in star-forming galaxies is flat or decreases over the same time period. Modest mass growth by a factor of 2 of individual quiescent galaxies can explain roughly half of the strong density evolution at M>10^11 solar masses, due to the steepness of the exponential tail of the mass function. The rest of the density evolution of massive, quiescent galaxies is likely due to transformation (e.g. quenching) of the massive star-forming population, a conclusion which is consistent with the density evolution we observe for the star-forming galaxies themselves, which is flat or decreasing with cosmic time. Modest mass growth does not explain the evolution of less massive quiescent galaxies (~10^10.5 solar masses), which show a similarly steep increase in their number densities. The less massive quiescent galaxies are therefore continuously formed by transforming galaxies from the star-forming population

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