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arXiv 1902.09548astro-ph.GA
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早期宇宙中的被动星系:CANDELS GOODS-South场中z~3-5候选星系的ALMA确认

Passive galaxies in the early Universe: ALMA confirmation of z~3-5 candidates in the CANDELS GOODS-South field

P. Santini, E. Merlin, A. Fontana, B. Magnelli, D. Paris, M. Castellano, A. Grazian, L. Pentericci, S. Pilo, M. Torelli

摘要:

在早期宇宙中选择红色的被动星系是非常具有挑战性的,特别是在z~3之后,并且关键是要限制对它们快速组装和突然关闭恒星形成过程负责的理论建模。本文分析了CANDELS-GOODS-South深场中30个星系中的26个星系的ALMA档案观测数据,通过仔细和保守的SED拟合分析,确定了这些星系在z~3-5处为被动星系。ALMA数据用于验证红色、尘埃但恒星形成源的潜在污染,由于类似的光学-近红外颜色,这些源可能进入样品。除了在<3sigma时的少数边缘检测外,我们只能推断出单个源和堆栈的上限。我们翻译成相应的SFR的ALMA连续测量,使用各种远红外模型。这些SFR进行了比较与预测的二次恒星形成的解决方案的光学拟合和预期的位置的恒星形成的主要序列。这一分析证实了9个候选人的被动性质,具有很高的信心,并表明,至少有一半的样本在统计意义上的分类是正确的。对于其余的来源,分析仍然没有结论,因为现有的ALMA数据不够深入,尽管叠加结果证实了它们的被动性质。尽管存在不确定性,这项工作提供了决定性的支持,在z~3以外的被动星系的存在。

英文摘要:

The selection of red, passive galaxies in the early Universe is very challenging, especially beyond z~3, and it is crucial to constrain theoretical modelling of the processes responsible for their rapid assembly and abrupt shut-down of the star formation. We present here the analysis of ALMA archival observations of 26 out of the 30 galaxies in the deep CANDELS GOODS-South field that we identified as passive at z~3-5 by means of a careful and conservative SED fitting analysis. ALMA data are used to verify the potential contamination from red, dusty but star--forming sources that could enter the sample due to similar optical--nearIR colours. With the exception of a few marginal detections at <3sigma, we could only infer upper limits, both on individual sources and on the stacks. We translated the ALMA continuum measurements into corresponding SFRs, using a variety of far-IR models. These SFRs are compared with those predicted by secondary star-forming solutions of the optical fits and with the expected position of the star formation Main Sequence. This analysis confirms the passive nature of 9 candidates with high confidence and suggests that the classification is correct for at least half of the sample in a statistical sense. For the remaining sources the analysis remain inconclusive because available ALMA data is not deep enough, although the stacking results corroborate their passive nature. Despite the uncertainties, this work provides decisive support to the existence of passive galaxies beyond z~3.

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