论文标题
追踪星系中的总分子气体：[CII]和涂层气体
Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas
论文作者
论文摘要
尽管CO（1-0）过渡通常用于推断星系中的总分子氢，但尽管发生了恒星形成，但在低金属度星系中检测到挑战。相反，[CII] 158微米线相对较明亮，突出了H2的潜在重要储层，该储层不是由CO（1-0）所追踪的，而是位于C+ - 发射区域。我们探索了一种量化星系中总H2质量（MH2）的方法，并了解哪些参数控制着涂层气体储层。我们以观察到的数量（例如[OI]，[CI]，CO（1-0），[CII]，总红外发光度和总MH2的含量而言，我们介绍了密度，辐射场和金属性的云网格，并提供基于这些模型的食谱，以得出从观测值中得出总MH2质量估计。这些模型应用于Herschel Dwarf Galaxy调查，将每个星系的总MH2提取与根据观察到的CO（1-0）线确定的H2进行比较。尽管CO（1-0）追踪的H2可以忽略不计，但[CII] 158微米线可以追踪总H2。在矮星系中，CO（1-0）未追踪总H2质量的70％至100％，而是由[CII] 158微米线路良好的。共黑气体质量分数与观察到的L [CII]/LCO（1-0）比相关。提出了[CII]发光度到总H2的转化因子，并提出了新的CO到总-MH2转换因子作为金属性的函数。考虑到CO和[CII]观测值，提供了一个配方来量化星系中H2的总质量。考虑到这种涂层H2气体，我们发现形成矮星系的恒星现在属于Schmidt-Kennicutt的关系。它们的恒星形成效率相当正常，因为在引入总H2的[CII]量度时，它们形成恒星的储层现在更加巨大，而共同发射区域中H2的量很小。
While the CO(1-0) transition is often used to deduce the total molecular hydrogen in galaxies, it is challenging to detect in low metallicity galaxies, in spite of the star formation taking place. In contrast, the [CII] 158 micron line is relatively bright, highlighting a potentially important reservoir of H2 that is not traced by CO(1-0), but residing in the C+ - emitting regions. We explore a method to quantify the total H2 mass (MH2) in galaxies and learn what parameters control the CO-dark gas reservoir. We present Cloudy grids of density, radiation field and metallicity in terms of observed quantities, such as [OI], [CI], CO(1-0), [CII], total infrared luminosity and the total MH2 and provide recipes based on these models to derive total MH2 mass estimates from observations. The models are applied to the Herschel Dwarf Galaxy Survey, extracting the total MH2 for each galaxy which is compared to the H2 determined from the observed CO(1-0) line. While the H2 traced by CO(1-0) can be negligible, the [CII] 158 micron line can trace the total H2. 70% to 100% of the total H2 mass is not traced by CO(1-0) in the dwarf galaxies, but is well-traced by [CII] 158 micron line. The CO-dark gas mass fraction correlates with the observed L[CII]/LCO(1-0) ratio. A conversion factor for [CII] luminosity to total H2 and a new CO-to-total-MH2 conversion factor, as a function of metallicity, is presented. A recipe is provided to quantify the total mass of H2 in galaxies, taking into account the CO and [CII] observations. Accounting for this CO-dark H2 gas, we find that the star forming dwarf galaxies now fall on the Schmidt-Kennicutt relation. Their star-forming efficiency is rather normal, since the reservoir from which they form stars is now more massive when introducing the [CII] measures of the total H2, compared to the little amount of H2 in the CO-emitting region.
