论文标题
星系中的中央分子区域：密集气体示踪剂HCN，HNC和HCO+的多译本调查
Central molecular zones in galaxies: multitransition survey of dense gas tracers HCN, HNC, and HCO+
论文作者
论文摘要
在覆盖HCN和HCO+（130个星系）和HNC（94个星系）的多运输数据库中，包括46个正常星系的新HCN，HNC和HCO+测量值。近线性的光度关系由距离效应主导，不反映星系物理特性。单个星系在其亮度和线比都显示出显着的分散体。线比与亮度或其他线比的相关性不太相关。仅HCN和HCO+的归一化J-转换梯子以及J = 1-0 12CO/13CO同位素比率与CO和FARRARERARE（FIR）发光呈正相关。 HCN和HCO+分子具有非常相似的强度，并追踪相同的气体。在主动核主导的星系中，HCO+强度相对于HCN强度降低。仅一小部分CO发射与HCN和HCO中的气体直接相关，但即使是该气体的很大一部分似乎是透明的分子气体。在观察到的星系中心中，HCN/CO线强度比不是致密气体分数的代理。同样，FIR/HCN和FIR/CO比率也不是恒星形成效率的代理。观察到的分子线发射与大量机械加热增强的UV-Photon加热完全一致。通过HCN和HCO+采样的分子气体具有低的动力学温度t（kin）= 10-50 K，低密度N（H）= 10^4-10^5 cm^（-3），地面态线中的光学深度较低。 CO采样的大多数气体的密度降低了一到两个数量级。对于0.5的机械加热部分，仅需要G = 300 GO的适度能量输入。对恒星形成的适当理解需要比单个HCN或CO过渡的强度更适当地确定气体质量。
New HCN, HNC, and HCO+ measurements of 46 normal galaxies in transitions up to J=4-3 are included in a multitransition database covering HCN and HCO+ (130 galaxies) and HNC (94 galaxies). The near-linear luminosity relations are dominated by distance effects and do not reflect galaxy physical properties. Individual galaxies show significant dispersion in both their luminosity and line ratio. Line ratios do not correlate well with either luminosities or other line ratios. Only the normalized J-transition ladders of HCN and HCO+ and the J=1-0 12CO/13CO isotopologue ratio are positively correlated with CO and far infrared (FIR) luminosity. The HCN and HCO+ molecules have very similar intensities and trace the same gas. In galaxies dominated by an active nucleus, HCO+ intensities are depressed relative to HCN intensities. Only a small fraction of the CO emission is directly associated with gas emitting in HCN and HCO, yet a significant fraction of even that gas appears to be translucent molecular gas. In the observed galaxy centers, the HCN/CO line intensity ratio is not a proxy for the dense gas fraction. Likewise, the FIR/HCN and FIR/CO ratios are not proxies for the star formation efficiency. The observed molecular line emission is fully consistent with UV-photon heating boosted by significant mechanical heating. The molecular gas sampled by HCN and HCO+ has low kinetic temperatures T(kin)=10-50 K, low densities n(H)=10^4-10^5 cm^(-3), and low optical depths in the ground-state lines. Most of the gas sampled by CO has densities lower by one to two orders of magnitude. For a mechanical heating fraction of 0.5, a modest energy input of only G=300 Go is required. A proper understanding of star formation requires a more appropriate determination of the gas mass than provided by the intensities of individual HCN or CO transitions.
