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arXiv 1503.06107astro-ph.GA
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z~1.7最大质量星系的恒星形成和猝灭

Star formation and quenching among the most massive galaxies at z~1.7

Chiara Mancini, Alvio Renzini, Emanuele Daddi, Giulia Rodighiero, Stefano Berta, Norman Grogin, Dale Kocevski, Anton Koekemoer

摘要:

我们对GOODS-South场中56个星系在1.4 < z < 2处的完整质量(M*>10^11 M_sun)样本进行了详细的逐对象研究,表明MIPS/24 um图像中的精确去混合对于正确分配每个星系的恒星形成率(SFR)至关重要,而自动程序通常会失败。这尤其适用于SFR低于主序列(MS)值的星系,这可能是在他们的淬火阶段。在那之后,样本在形成恒星的星系之间均匀分裂,形成的恒星比例为MS的4倍(约45%),而SFR小10-1000倍的亚MS星系(约55%)。我们没有发现一个定义明确的中间类,MS以下的瞬态对象,这表明一个大质量MS星系转化为淬灭的残骸可能需要相对较短的时间(<1 Gyr),尽管应该以同样的方式分析更大的样本,以确定淬灭时间尺度的精确限制。X射线探测到的活动星系核占样本的30%,在恒星形成和淬灭星系中都有发现。形态学分析显示,我们的大质量天体中约有50%是以凸起为主的,几乎所有具有相关凸起成分的MS星系都拥有AGN。我们还发现,在许多膨胀主导的系统中,亚MS SFR,提供支持的概念,即膨胀的增长,活动星系核活动和恒星形成的淬火是密切相关的。

英文摘要:

We have conducted a detailed object-by-object study of a mass-complete (M*>10^11 M_sun) sample of 56 galaxies at 1.4 < z < 2 in the GOODS-South field, showing that an accurate de-blending in MIPS/24um images is essential to properly assign to each galaxy its own star formation rate (SFR), whereas an automatic procedure often fails. This applies especially to galaxies with SFRs below the Main Sequence (MS) value, which may be in their quenching phase. After that, the sample splits evenly between galaxies forming stars within a factor of 4 of the MS rate (~45%), and sub-MS galaxies with SFRs ~10-1000 times smaller (~55%). We did not find a well defined class of intermediate, transient objects below the MS, suggesting that the conversion of a massive MS galaxy into a quenched remnant may take a relatively short time (<1 Gyr), though a larger sample should be analyzed in the same way to set precise limits on the quenching timescale. X-ray detected AGNs represent a ~30% fraction of the sample, and are found among both star-forming and quenched galaxies. The morphological analysis revealed that ~50% of our massive objects are bulge-dominated, and almost all MS galaxies with a relevant bulge component host an AGN. We also found sub-MS SFRs in many bulge-dominated systems, providing support to the notion that bulge growth, AGN activity and quenching of star formation are closely related to each other.

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