CO Multi-line Imaging of Nearby Galaxies (COMING). IX. 12CO(J=2-1)/12CO(J=1-0) line ratio on kiloparsec scales
CO Multi-line Imaging of Nearby Galaxies (COMING). IX. 12CO(J=2-1)/12CO(J=1-0) line ratio on kiloparsec scales
复制标题
附近星系的 CO 多线成像（即将推出）。
DOI：
10.1093/pasj/psaa119
复制
发表时间：
2021
影响因子：
2.3
通讯作者：
Kobayashi Masato I N
中科院分区：
文献类型：
--
作者：
Yajima Yoshiyuki;Sorai Kazuo;Miyamoto Yusuke;Muraoka Kazuyuki;Kuno Nario;Kaneko Hiroyuki;Takeuchi Tsutomu T;Yasuda Atsushi;Tanaka Takahiro;Morokuma-Matsui Kana;Kobayashi Masato I N
虽然分子气体质量通常是从12 CO（J= 1-0）--探测分子气体的最基本的谱线--推导出来的，但它通常是从12 CO（J = 2-1）推导出来的，假设12 CO（J= 2-1）12 CO（J= 1-0）谱线比（R2/1）是恒定的。利用野边山45米射电望远镜和IRAM 30米望远镜获得的12 CO观测资料，给出了24个邻近星系的R2/1的变化以及R2/1为常数的假设的影响。所有星系的R ~（2/1）的中位数为0.61，~（12）CO（J= 1-0）积分强度对R ~（2/1）的加权平均值为0.66，标准差为0.19。R2/1的径向变化表明，在所有星系的汇编中，它在2001 kpc的内部很高（0.80），而在盘中的中值几乎恒定在0.60。在常数R ~（2 - 1）为0.7的情况下，我们发现由~（12）CO（J= 2-1）导出的总分子气体质量被低估/高估了约20%，最多高估35%。每个星系内分子气体面密度的离散度增大了30%，最多增大了120%。在24个星系中，有17个星系的12 CO（J= 2-1）空间分辨Kennicutt-Schmidt关系指数被低估了10%-20%，最多39%; R2/1与恒星形成率和红外颜色有很好的正相关，与分子气体耗尽时间有很好的负相关。R2/1随动力学温度（Tkin）的升高有明显的增加趋势。此外，我们发现，不仅Tkin，而且分子气体的压力是重要的，在理解的变化R2/1。当讨论由12 CO（J= 2-1）而不是12 CO（J= 1-0）推断的分子气体质量和分子气体性质时，应特别注意。
While molecular gas mass is usually derived from12CO(J= 1–0)—the most fundamental line for exploring molecular gas—it is often derived from12CO(J= 2–1) assuming a constant12CO(J= 2–1)12CO(J= 1–0) line ratio (R2/1). We present variations ofR2/1and effects of the assumption thatR2/1is a constant in 24 nearby galaxies using12CO data obtained with the Nobeyama 45 m radio telescope and IRAM 30 m telescope. The median ofR2/1for all galaxies is 0.61, and the weighted mean ofR2/1by12CO(J= 1–0) integrated intensity is 0.66 with a standard deviation of 0.19. The radial variation ofR2/1shows that it is high (∼0.8) in the inner ∼1 kpc while its median in disks is nearly constant at 0.60 when all galaxies are compiled. In the case that the constantR2/1of 0.7 is adopted, we found that the total molecular gas mass derived from12CO(J= 2–1) is underestimated/overestimated by ∼20%, and at most by 35%. The scatter of molecular gas surface density within each galaxy becomes larger by ∼30%, and at most by 120%. Indices of the spatially resolved Kennicutt–Schmidt relation by12CO(J= 2–1) are underestimated by 10%–20%, at most 39%, in 17 out of 24 galaxies.R2/1has good positive correlations with star-formation rate and infrared color, and a negative correlation with molecular gas depletion time. There is a clear tendency of increasingR2/1with increasing kinetic temperature (Tkin). Further, we found that not onlyTkinbut also pressure of molecular gas is important in understanding variations ofR2/1. Special considerations should be made when discussing molecular gas mass and molecular gas properties inferred from12CO(J= 2–1) instead of12CO(J= 1–0).