Now You See It, Now You Don’t: Star Formation Truncation Precedes the Loss of Molecular Gas by ∼100 Myr in Massive Poststarburst Galaxies at z ∼ 0.6
Now You See It, Now You Don’t: Star Formation Truncation Precedes the Loss of Molecular Gas by ∼100 Myr in Massive Poststarburst Galaxies at z ∼ 0.6
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DOI：
10.3847/1538-4357/ac3dfa
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
R. Bezanson;J. Spilker;K. Suess;David J. Setton;R. Feldmann;J. Greene;M. Kriek;D. Narayanan;M. Verrico
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作者：
R. Bezanson;J. Spilker;K. Suess;David J. Setton;R. Feldmann;J. Greene;M. Kriek;D. Narayanan;M. Verrico
我们利用ALMA对13个大质量星系(M*≳1011M⊙)在z∼0.6时CO(2-1)的观测来限制星系在其主要恒星形成幕熄灭后不久的分子气体含量。本研究中的星暴后星系是从斯隆数字巡天的光谱样本(数据发布14)中根据它们的光谱形状挑选出来的，作为研究中等z星系猝灭的一部分：气体，安古L→Ar动量和演化(SQuIGGL⃗E)计划。早期的结果表明，两个星暴后星系拥有大量的氢气储存库，尽管它们的推测恒星形成率(SFR)很低。在这里，我们将这种分析扩展到一个更大的统计样本，包括13个星系。探测到了6个主要目标(45%)，其中MH2≳为109M⊙。考虑到它们的高质量，根据解析的指数递减恒星形成历史得出的较低的恒星质量估计，这个质量极限对应于<FH2≡MH2/M*>∼7%或∼14%的平均气体分数。气体分数与Dn4000光谱指数相关，表明冷气藏自爆发以来随着时间的推移而减少，正如在局部K+A星系中所发现的那样。从灵活的恒星群综合模型得到的恒星形成历史支持这一经验发现：在观测之前猝灭≲150Myr的星系主机可以检测到CO(2-1)发射，而更老的星暴后星系则没有被检测到。样品中大的H2气藏和低的SFR表明，恒星形成的猝灭先于冷气藏的消失。然而，在接下来的100-200Myr期间，SQuigGL⃗E星系需要额外和有效的加热或移除冷气体，以使它们的低SFR符合标准的H2标度关系。
We use ALMA observations of CO(2–1) in 13 massive (M * ≳ 1011 M ⊙) poststarburst galaxies at z ∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, angu L→ar momentum, and Evolution ( SQuIGGL⃗E ) program. Early results showed that two poststarburst galaxies host large H2 reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, with MH2≳109 M ⊙. Given their high stellar masses, this mass limit corresponds to an average gas fraction of 〈fH2≡MH2/M*〉∼7% or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with the D n 4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H2 reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, the SQuIGGL⃗E galaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H2 scaling relations.