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arXiv 0809.1426astro-ph
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E-CDFS中大质量星系比恒星形成率到z ~ 1.8的演化

The evolution of the specific star formation rate of massive galaxies to z ~ 1.8 in the E-CDFS

Maaike Damen, Ivo Labbe, Marijn Franx, Pieter G. van Dokkum, Edward N. Taylor, Eric J. Gawiser

摘要:

在扩展的Chandra深场南(E-CDFS)中研究了中红外(IR)选择星系的恒星形成率(SFR)的演化。我们使用U-K GaBoDS和MUSYC数据,来自SIMPLE的深IRAC观测和来自FIDEL的深MIPS数据的组合。这个独特的多波长数据集使我们能够研究大质量星系的SFR历史,红移z ~ 1.8。我们确定恒星形成率使用的静止帧紫外光度从年轻的,热的恒星和总的红外光度遮蔽恒星形成从MIPS 24微米通量。我们发现,在所有的红移的星系具有较高的质量有实质上较低的特定的恒星形成率比低质量的星系。平均特定恒星形成率随着红移而增加,并且所有星系的倾斜率都相似(大致为(1+z)^{n},n = 5.0 +/- 0.4)。它似乎不是星系质量的强函数。利用质量M_*> 10^11 M_sun的星系子样本,我们测量了恒星形成被淬灭的星系的比例。我们认为当一个星系的比恒星形成率不超过1/(3 x t_H)时,该星系处于静止状态,其中t_H是哈勃时间。被定义为静止星系的比例随着红移到z ~ 1.8而减少。我们发现,根据我们的标准,在该红移处,19 +/-9%的M_* > 10^11 M_太阳源将被认为是静止的。

英文摘要:

We study the evolution of the star formation rate (SFR) of mid-infrared (IR) selected galaxies in the extended Chandra Deep Field South (E-CDFS). We use a combination of U-K GaBoDS and MUSYC data, deep IRAC observations from SIMPLE, and deep MIPS data from FIDEL. This unique multi-wavelength data set allows us to investigate the SFR history of massive galaxies out to redshift z ~ 1.8. We determine star formation rates using both the rest-frame ultraviolet luminosity from young, hot stars and the total IR luminosity of obscured star formation obtained from the MIPS 24 um flux. We find that at all redshifts the galaxies with higher masses have substantially lower specific star formation rates than lower mass galaxies. The average specific star formation rates increase with redshift, and the rate of incline is similar for all galaxies (roughly (1+z)^{n}, n = 5.0 +/- 0.4). It does not seem to be a strong function of galaxy mass. Using a subsample of galaxies with masses M_*> 10^11 M_sun, we measured the fraction of galaxies whose star formation is quenched. We consider a galaxy to be in quiescent mode when its specific star formation rate does not exceed 1/(3 x t_H), where t_H is the Hubble time. The fraction of quiescent galaxies defined as such decreases with redshift out to z ~ 1.8. We find that, at that redshift, 19 +/-9 % of the M_* > 10^11 M_sun sources would be considered quiescent according to our criterion.

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