Measuring the Average Molecular Gas Content of Star-forming Galaxies at z = 3–4
Measuring the Average Molecular Gas Content of Star-forming Galaxies at z = 3–4
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DOI：
10.3847/1538-4357/ac01d7
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发表时间：
2021-05
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通讯作者：
L. Boogaard;R. Bouwens;D. Riechers;P. P. van der Werf-P.;R. Bacon;J. Matthee;M. Stefanon;A. Feltre;M. Maseda;H. Inami;M. Aravena;J. Brinchmann;C. Carilli;T. Contini;R. Decarli;J. Gonz'alez-L'opez;T. Nanayakkara;F. Walter
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作者：
L. Boogaard;R. Bouwens;D. Riechers;P. P. van der Werf-P.;R. Bacon;J. Matthee;M. Stefanon;A. Feltre;M. Maseda;H. Inami;M. Aravena;J. Brinchmann;C. Carilli;T. Contini;R. Decarli;J. Gonz'alez-L'opez;T. Nanayakkara;F. Walter
我们研究了MUSE哈勃超深场（HUDF）巡天中z = 3-4的24个恒星形成星系的分子气体含量，恒星质量中位数为109.1 M ⊙。根据它们的Lyα λ1216发射和HF 160 W波段星等选择，这些星系的平均EWLyα0 = 20 λ，低于Lyα发射体的典型选择阈值（EWLyα0>25 λ），并且具有类似于Lyman-break星系的静止帧紫外光谱。我们使用KMOS和MOSFIRE的静止框架光谱学，以及MUSE观测到的紫外特征，来确定系统红移，它与Lyα的偏移量为<$Δv（Lyα）<$= 346 km s−1，范围为100至600 km s−1。叠加来自HUDF的阿尔马光谱巡天的12 CO J = 4 → 3和[Ci] 3 P1 → 3 P0（以及更高J的CO线），我们确定了线亮度的3σ上限分别为4.0 × 108 K km s− 1 pc 2和5.6 × 108 K km s− 1 pc 2（线宽为300 km s−1）。将1.2 mm和3 mm尘埃连续通量密度叠加，得到3σ上限分别为9 μJy和1.2 μJy。推断的气体分数，假设的“银河系”的CO-到-H2的转换因子和气体-尘埃比，与先前确定的比例关系的紧张局势。这意味着更高的α CO ≥ 10和δ GDR ≥ 1200，与这些星系的太阳下金属丰度估计值（12+log（O/H）<$7.8 ±0.2）一致。z ≥ 3恒星形成星系的低金属丰度可能因此使通过CO或尘埃排放揭示其冷气体非常具有挑战性，从而阻碍了对替代示踪剂的进一步探索，例如[C ii]。
We study the molecular gas content of 24 star-forming galaxies at z = 3–4, with a median stellar mass of 109.1 M ⊙, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyα λ1216 emission and H F160W-band magnitude, the galaxies show an average 〈EWLyα0〉≈20 Å, below the typical selection threshold for Lyα emitters ( EWLyα0>25 Å), and a rest-frame UV spectrum similar to Lyman-break galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyα by 〈Δv(Lyα)〉 = 346 km s−1, with a 100 to 600 km s−1 range. Stacking 12CO J = 4 → 3 and [C i]3P1 → 3P0 (and higher-J CO lines) from the ALMA Spectroscopic Survey of the HUDF, we determine 3σ upper limits on the line luminosities of 4.0 × 108 K km s−1pc2 and 5.6 × 108 K km s−1pc2, respectively (for a 300 km s−1 line width). Stacking the 1.2 mm and 3 mm dust-continuum flux densities, we find a 3σ upper limits of 9 μJy and 1.2 μJy, respectively. The inferred gas fractions, under the assumption of a “Galactic” CO-to-H2 conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher α CO ≥ 10 and δ GDR ≥ 1200, consistent with the subsolar metallicity estimated for these galaxies ( 12+log(O/H)≈7.8±0.2 ). The low metallicity of z ≥ 3 star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [C ii].