First Detection of the Molecular Cloud Population in the Extended Ultraviolet Disk of M83
First Detection of the Molecular Cloud Population in the Extended Ultraviolet Disk of M83
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DOI：
10.3847/1538-4357/ac9dfc
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发表时间：
2022-08
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通讯作者：
J. Koda;L. Watson;F. Combes;M. Rubio;S. Boissier;M. Yagi;D. Thilker;A. Lee;Y. Komiyama;K. Morokuma-Matsui;C. Verdugo
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作者：
J. Koda;L. Watson;F. Combes;M. Rubio;S. Boissier;M. Yagi;D. Thilker;A. Lee;Y. Komiyama;K. Morokuma-Matsui;C. Verdugo
本文报道了利用阿塔卡玛大型毫米/亚毫米波阵列对旋涡星系M83扩展紫外（XUV）盘中23个分子云的CO（J = 3−2）探测。所观察到的1 kpc ~ 2区域约为圆盘光学半径（R 25）的1.24倍，其中CO（J = 2-1）以前未被检测到。检测和未检测，以及该地区的星星形成（SF）活动的水平，可以解释一致，如果云的质量分布常见的银河系云，如猎户座A-与恒星形成密集的团块嵌入在厚层的散装分子气体，但在低金属度制度，他们的外层是CO-缺乏和CO-黑暗。由CO（3−2）估算的云和团的质量范围分别为8.2 × 102 ~ 2.3 × 104 M和2.7 × 102 ~ 7.5 × 103 M。最大质量的云在星星形成活动和质量上看起来与猎户座A相似，如果云的质量结构是常见的，那么就像预期的那样。在XUV盘中的整体低SF活性可能是由于分子相中气体的相对短缺。云的分布像链条一样，长度可达600 pc（或更长），这表明云形成的触发因素是大尺度的。共同的云质量结构也证明了使用高J CO跃迁来追踪云或星系的总气体质量的合理性，即使在高z宇宙中也是如此。这项研究首次证明，即使在低金属含量的环境中，CO（3−2）也是分子云的有效示踪剂。
We report a CO(J = 3−2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with the Atacama Large Millimeter/submillimeter Array. The observed 1 kpc2 region is at about 1.24 times the optical radius (R 25) of the disk, where CO(J = 2–1) was previously not detected. The detection and nondetection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A—with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3−2), range from 8.2 × 102 to 2.3 × 104 M ⊙ and from 2.7 × 102 to 7.5 × 103 M ⊙, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is common. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The common cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3−2) is an efficient tracer of molecular clouds even in low-metallicity environments.