z~2处的恒星形成和尘埃遮蔽：缩小黎明时的星系
Star formation and dust obscuration at z~2: galaxies at the dawn of downsizing
摘要：
我们提出的第一个研究结果，旨在限制恒星形成率和尘埃含量的星系在z~2。我们使用从COSMOS调查中提取的BzK选择的恒星形成星系样本，在从样本中去除AGN污染物后，对其1.4 GHz射电连续谱进行叠加分析，作为不同恒星星族属性的函数。尘埃无偏恒星形成率来自无线电通量假设当地的无线电-红外相关。这些工作的主要结果是：（1）比恒星形成率在恒星质量为1dex的范围内和探测到的最大恒星质量范围内是恒定的;（2）尘埃衰减是星系恒星质量的强函数，质量越大的星系比质量较低的天体更容易被遮蔽;（3）单一的紫外消光值适用于所有星系将导致严重低估大质量星系的SFR; iv）根据Calzetti公式对观测到的紫外光度进行尘埃衰减校正，结果与射电导出的结果非常一致; v）我们样品的平均比恒星形成率随着红移从z=2.3到1.4的减小而稳定地减小~4倍，并且在本宇宙中减小~40倍。这些经验的SFR将导致星系的质量急剧过度增长，如果保持所有的方式低红移，我们认为这不会发生，因为恒星的形成是逐步淬火，可能从最大质量的星系开始。
英文摘要：
We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z~2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ~4 with decreasing redshift from z=2.3 to 1.4 and a factor of ~40 down the local Universe. These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.
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