The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Multiband Constraints on Line-luminosity Functions and the Cosmic Density of Molecular Gas
The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Multiband Constraints on Line-luminosity Functions and the Cosmic Density of Molecular Gas
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DOI：
10.3847/1538-4357/abaa3b
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发表时间：
2020-09
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通讯作者：
R. Decarli;M. Aravena;L. Boogaard;C. Carilli;J. Gonz'alez-L'opez;F. Walter;P. Cortés;P. Cox;E. D. Cunha;E. Daddi;T. Díaz-Santos;J. Hodge;H. Inami;M. Neeleman;M. Novak;P. Oesch;G. Popping;D. Riechers;I. Smail;B. Uzgil;P. Werf;J. Wagg;A. Weiss
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作者：
R. Decarli;M. Aravena;L. Boogaard;C. Carilli;J. Gonz'alez-L'opez;F. Walter;P. Cortés;P. Cox;E. D. Cunha;E. Daddi;T. Díaz-Santos;J. Hodge;H. Inami;M. Neeleman;M. Novak;P. Oesch;G. Popping;D. Riechers;I. Smail;B. Uzgil;P. Werf;J. Wagg;A. Weiss
我们介绍了利用ALMA光谱测量(ASPECS)在哈勃超深场中进行的CO和原子精细结构谱线光度函数分析。ASPECS由两个空间重叠的马赛克组成，覆盖整个ALMA 3 mm和1.2 mm频段。我们将1.2 mm数据立方体的线候选搜索结果与先前从3 mm立方体获得的结果相结合。我们的分析表明，在3 mm处观测到的线通量中，∼的80%来自z=1-3(“宇宙正午”)的CO(2-1)或CO(3-2)发射体。在1.2 mm处，超过一半的线通量来自中间-J CO跃迁(JUP=3-6)；∼12%来自中性碳线；-lt；1%来自单一电离碳，[C2]。这意味着，在再电离时代，未来的[C II]强度图调查将需要考虑一个非常重要的CO前景。在1.2 mm处探测的CO光度函数表明，在给定线光度(单位为L)下，数密度随JUP和红移的增加而减小。通过比较固定红移下不同CO跃迁的CO光度函数，揭示了直到z∼4的星系平均处于亚热状态。此外，不同红移下同一跃迁的CO光度函数的比较表明，演化不是由激发驱动的。星系中分子气体的宇宙密度ρH2呈现红移演化，从高红移到z∼1.5，然后是因子∼6下降到现在。这与宇宙恒星形成率密度的演化定性一致，表明在对恒星形成星系群进行平均后，分子气体耗尽时间随红移而近似不变。
We present a CO and atomic fine-structure line-luminosity function analysis using the ALMA Spectroscopic Survey (ASPECS) in the Hubble Ultra Deep Field. ASPECS consists of two spatially overlapping mosaics that cover the entire ALMA 3 mm and 1.2 mm bands. We combine the results of a line-candidate search of the 1.2 mm data cube with those previously obtained from the 3 mm cube. Our analysis shows that ∼80% of the line flux observed at 3 mm arises from CO(2–1) or CO(3–2) emitters at z = 1–3 (“cosmic noon”). At 1.2 mm, more than half of the line flux arises from intermediate-J CO transitions (Jup = 3–6); ∼12% from neutral carbon lines; and <1% from singly ionized carbon, [C ii]. This implies that future [C ii] intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2 mm show a decrease in the number density at a given line luminosity (in units of L′) at increasing Jup and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal subthermal conditions on average in galaxies up to z ∼ 4. In addition, the comparison of the CO luminosity functions for the same transition at different redshifts reveals that the evolution is not driven by excitation. The cosmic density of molecular gas in galaxies, ρH2, shows a redshift evolution with an increase from high redshift up to z ∼ 1.5 followed by a factor ∼6 drop down to the present day. This is in qualitative agreement with the evolution of the cosmic star formation rate density, suggesting that the molecular gas depletion time is approximately constant with redshift, after averaging over the star-forming galaxy population.