CO Excitation in High-z Main-sequence Analogues: Resolved CO(4−3)/CO(3−2) Line Ratios in DYNAMO Galaxies
CO Excitation in High-z Main-sequence Analogues: Resolved CO(4−3)/CO(3−2) Line Ratios in DYNAMO Galaxies
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DOI：
10.3847/1538-4357/acb3b2
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发表时间：
2023-01
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通讯作者：
L. Lenkić;A. Bolatto;D. Fisher;R. Abraham;K. Glazebrook;R. Herrera-Camus;R. C. Levy;D. Obreschkow;C. Volpert
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作者：
L. Lenkić;A. Bolatto;D. Fisher;R. Abraham;K. Glazebrook;R. Herrera-Camus;R. C. Levy;D. Obreschkow;C. Volpert
一氧化碳的谱线能量分布包含了形成恒星的氢分子的物理条件的信息；然而，与局部辐射场性质的关系却没有得到很好的约束。利用~ 1-2 kpc尺度的Atacama大型毫米波阵列对CO（3−2）和CO（4−3）的观测，我们表征了z ~ 1-2处主序星系局部类似物的CO(4−3)/CO（3−2）线比，这些线比来自新组装大质量物体动力学（DYNAMO）样本。我们测量了每个星系圆盘上的CO(4−3)/CO(3−2)，发现样本的中位数线比为r43 = 0.54−0.15+0.16。这比文献中对局部恒星形成星系的估计要高，并且与多个证据线一致，表明DYNAMO星系尽管位于局部宇宙中，但在z ~ 1-2处与主序星系相似。与现有的低分辨率CO（1−0）观测值相比，我们发现r41和r31分别在~ 0.2-0.3和~ 0.4-0.8范围内。我们将千帕秒尺度的分辨线比测量结果与哈勃太空望远镜对Hα的观测结果结合起来，研究了Hα与恒星形成速率表面密度的关系，并将这种关系与模型的预期进行了比较。CO(4−3)/CO（3−2）随恒星形成速率和表面密度的增加而增加；然而，在我们探测的恒星形成速率表面密度范围内，特别是在较低范围内，模型高估了线比。最后，利用高分辨率机载宽带相机和场成像远红外谱仪进行的平流层红外天文观测显示，尘埃温度较低，并且相对于红外总光度没有[Cii]发射缺陷。
The spectral line energy distribution of carbon monoxide contains information about the physical conditions of the star-forming molecular hydrogen gas; however, the relation to local radiation field properties is poorly constrained. Using ∼1–2 kpc scale Atacama Large Millimeter Array observations of CO(3−2) and CO(4−3), we characterize the CO(4−3)/CO(3−2) line ratios of local analogues of main-sequence galaxies at z ∼ 1–2, drawn from the DYnamics of Newly Assembled Massive Objects (DYNAMO) sample. We measure CO(4−3)/CO(3−2) across the disk of each galaxy and find a median line ratio of R 43 = 0.54 −0.15+0.16 for the sample. This is higher than literature estimates of local star-forming galaxies and is consistent with multiple lines of evidence that indicate DYNAMO galaxies, despite residing in the local universe, resemble main-sequence galaxies at z ∼ 1–2. Comparing with existing lower-resolution CO(1−0) observations, we find R 41 and R 31 values in the range ∼0.2–0.3 and ∼0.4–0.8, respectively. We combine our kiloparsec-scale resolved line ratio measurements with Hubble Space Telescope observations of Hα to investigate the relation to the star formation rate surface density and compare this relation to expectations from models. We find increasing CO(4−3)/CO(3−2) with increasing star formation rate surface density; however, models overpredict the line ratios across the range of star formation rate surface densities we probe, in particular at the lower range. Finally, Stratospheric Observatory for Infrared Astronomy observations with the High-resolution Airborne Wideband Camera Plus and Field-Imaging Far-Infrared Line Spectrometer reveal low dust temperatures and no deficit of [Cii] emission with respect to the total infrared luminosity.