论文标题
螺旋星系NGC中分子气的多线研究2903
Multiple-line study of molecular gas in spiral galaxy NGC 2903
论文作者
论文摘要
具有辐射转移模型的多个分子线是探测星系中星形气体物理的强大工具。我们使用低J CO线，即12CO（1-0），12CO（2-1），12CO（3-2），13CO（1-0）和HCN（1-0）研究了螺旋星系NGC 2903中心的气体性质。我们应用非局部热力学平衡辐射转移代码，以得出束平均分子气体性能。我们使用两种方法（即卡方最小化和可能性）来定义代表观察到的线比最佳的最佳模型。线比诊断表明NGC 2903中心的CO气体比螺旋，星状和早期型星系（ETGS）相似，密集的气体分数相似，而星系中心的气体比ETGS的气体温暖，比Starbursts的气体温暖。 Based on the best-fitting model results, we find that the beam-averaged gas kinetic temperature is T_K = 20 K, H_2 volume number density is log(n(H_2)) = 4.2 cm-3 , and CO column number density is log(N(CO)) = 19.0 cm-2 in the centre of NGC 2903. Both methods, i.e. the line ratio diagnostics and modelling, indicate an ISM in the centre of NGC 2903具有中等温度和恒星形成活性（也由恒星形成速率支撑），具有相似密度气体分数的较薄的CO气体以及H_2体积数密度较高，与螺旋，ETG和Starburst相比。
Multiple molecular lines with radiative transfer modelling are a powerful tool to probe the physics of star-forming gas in galaxies. We investigate the gas properties in the centre of the spiral galaxy NGC 2903 using low-J CO lines, i.e. 12CO(1-0), 12CO(2-1), 12CO(3-2), 13CO(1-0), and HCN(1-0). We apply a nonlocal thermodynamic equilibrium radiative transfer code to derive beam-averaged molecular gas properties. We use two methods (i.e. chi-square minimizations and likelihood) to define the best model representing the observed line ratios best. The line ratio diagnostics suggest that CO gas in the centre of NGC 2903 is thinner and the dense gas fraction is similar compared to that of spirals, starburst, and early-type galaxies (ETGs), while the gas in the centre of the galaxy is warmer than that of ETGs and colder than that of starbursts. Based on the best-fitting model results, we find that the beam-averaged gas kinetic temperature is T_K = 20 K, H_2 volume number density is log(n(H_2)) = 4.2 cm-3 , and CO column number density is log(N(CO)) = 19.0 cm-2 in the centre of NGC 2903. Both methods, i.e. the line ratio diagnostics and modelling, indicate an ISM in the centre of NGC 2903 having intermediate temperature and star formation activity (also supported by star formation rates), thinner CO gas with similar dense gas fraction, and higher H_2 volume number density compared to that of spirals, ETGs, and starbursts.
