星系中的中心分子带：12 CO与13 CO的比率、碳收支和X因子
Central molecular zones in galaxies: 12CO-to-13CO ratios, carbon budget, and X factors
摘要：
本文介绍了126个邻近星系中心在各种J跃迁中的12 CO和13 CO的地面测量结果。至少在四条线上测量了60多个星系。前四个12 CO跃迁的平均相对强度为1.00：0.92：0.70：0.57。前三次跃迁的平均~（12）CO/~（13）CO比值分别为13.0、11.6和12.8。中心CO浓度的大小在地图上有很好的定义，但多孔径光度测定法却很难确定。使用辐射转移模型（RADEX），我们推导出模型气体参数，其中假设的碳元素丰度和碳气体贫化到灰尘是不确定性的主要原因。新的CO数据和公布的[CI]和[CII]数据表明，CO，Co，和C+分别代表星系中心分子星际介质中气相碳的三分之一。它们的平均束均中心分子氢柱密度为N（H2）=（1.5+/-0.2）× 10^（21）cm^（2）和CO到H2的转换因子通常比“标准”银河系盘值低十倍，平均X（CO）=（1.9+/-0.2）x 10^（19）cm^（2）/K km/s。相应的[CI]-H2因子比X（CO）高5倍，X[CI] =（9+/-2）x 10^（19）cm^（2）/K km/s。无法确定[CII]的唯一转换因子。星系中心的低分子气体含量相对于它们的CO强度被解释为大致相等的部分，由更高的中心气相碳丰度，气体温度升高，和更大的气体速度色散比发现在星系盘。
英文摘要：
This paper presents ground-based 12CO and 13CO measurements of 126 nearby galaxy centers in various J transitions. More than 60 galaxies were measured in at least four lines. The average relative intensities of the first four 12CO transitions are 1.00 : 0.92 : 0.70 : 0.57. The average 12CO-to-13CO ratios are 13.0, 11.6, and 12.8 for the first three transitiions. The sizes of central CO concentrations are well defined in maps, but poorly determined by multi-aperture photometry. Using radiative transfer models (RADEX), we derived model gas parameters, where the assumed carbon elemental abundances and carbon gas depletion onto dust are the main causes of uncertainty. The new CO data and published [CI] and [CII] data imply that CO, Co, and C+ each represent about one-third of the gas-phase carbon in the molecular interstellar medium in galaxy centers Their mean beam-averaged central molecular hydrogen column density is N(H2) = (1.5+/-0.2) x 10^(21) cm^(2) and CO-to-H2 conversion factors are typically ten times lower than the `standard' Milky Way disk value, with a mean X(CO) = (1.9+/-0.2) x 10^(19) cm^(2)/K km/s. The corresponding [CI]-to-H2 factor is five times higher than X(CO), with X[CI] = (9+/-2) x 10^(19) cm^(2)/K km/s. No unique conversion factor can be determined for [CII]. The low molecular gas content of galaxy centers relative to their CO intensities is explained in roughly equal parts by higher central gas-phase carbon abundances, elevated gas temperatures, and larger gas velocity dispersions than found in galaxy disks.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
