VLA–ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (VLASPECS): Total Cold Gas Masses and CO Line Ratios for z = 2–3 Main-sequence Galaxies
VLA–ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (VLASPECS): Total Cold Gas Masses and CO Line Ratios for z = 2–3 Main-sequence Galaxies
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DOI：
10.3847/2041-8213/ab9595
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发表时间：
2020-05
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通讯作者：
D. Riechers;L. Boogaard;R. Decarli;J. González-López;I. Smail;F. Walter;M. Aravena;C. Carilli;P. Cortés;P. Cox;T. Díaz-Santos;J. Hodge;H. Inami;R. Ivison;M. Kaasinen;J. Wagg;A. Weiss;P. Werf
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作者：
D. Riechers;L. Boogaard;R. Decarli;J. González-López;I. Smail;F. Walter;M. Aravena;C. Carilli;P. Cortés;P. Cox;T. Díaz-Santos;J. Hodge;H. Inami;R. Ivison;M. Kaasinen;J. Wagg;A. Weiss;P. Werf
利用美国国家科学基金会（NSF）的Karl G. Jansky甚大阵列（VLA），我们报告了在哈勃超深场（ASPECS）的阿塔卡马大型毫米/亚毫米阵列光谱调查中，在z = 2-3个星系中检测到的6个CO（J = 1→0）发射和一个上限。根据CO（J = 1→0）谱线强度，我们测得Mgas的总冷分子气体质量= (2.4 ~ 11.6)× 1010 (αCO/3.6)M⊙。我们还测量到CO（J = 3→2）与CO（J = 1→0）线的中位亮温比为r31 = 0.84±0.26，CO（J = 7→6）与CO（J = 1→0）线的中位亮温比为r71 < 0.05 ~ r71 = 0.17。这些结果表明CO（J = 3→2）选择的星系可能比CO（J = 1→0）选择的星系平均具有更高的CO线激发，基于有限的，目前从ASPECS和VLA高红移（COLDz）调查中获得的CO发光密度样本。这意味着先前基于CO（J = 3→2）测量的星系中冷气体的宇宙密度估计应该平均向下修正一个系数，即仅基于CO激励的假设。这一修正进一步改善了目前从线扫描调查中得到的关于宇宙历史上冷气体密度演化的最佳约束与隐含的特征气体耗尽时间之间的一致性。
Using the NSF’s Karl G. Jansky Very Large Array (VLA), we report six detections of CO(J = 1 → 0) emission and one upper limit in z = 2–3 galaxies originally detected in higher-J CO emission in the Atacama Large Millimeter/submillimeter Array Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). From the CO(J = 1 → 0) line strengths, we measure total cold molecular gas masses of Mgas = (2.4–11.6) × 1010 (αCO/3.6)M⊙. We also measure a median CO(J = 3 → 2) to CO(J = 1 → 0) line brightness temperature ratio of r31 = 0.84 ± 0.26, and a CO(J = 7 → 6) to CO(J = 1 → 0) ratio range of r71 < 0.05 to r71 = 0.17. These results suggest that CO(J = 3 → 2) selected galaxies may have a higher CO line excitation on average than CO(J = 1 → 0) selected galaxies, based on the limited, currently available samples from the ASPECS and VLA CO Luminosity Density at High Redshift (COLDz) surveys. This implies that previous estimates of the cosmic density of cold gas in galaxies based on CO(J = 3 → 2) measurements should be revised down by a factor of ≃2 on average based on assumptions regarding CO excitation alone. This correction further improves the agreement between the best currently existing constraints on the cold gas density evolution across cosmic history from line scan surveys, and the implied characteristic gas depletion times.