Molecular Star Formation Rate Indicators in Galaxies
Molecular Star Formation Rate Indicators in Galaxies
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DOI：
10.1086/588720
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发表时间：
2007-11
期刊：
影响因子：
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通讯作者：
D. Narayanan;T. J. Cox;Y. Shirley;R. Davé;L. Hernquist;C. Walker
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文献类型：
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作者：
D. Narayanan;T. J. Cox;Y. Shirley;R. Davé;L. Hernquist;C. Walker
我们推导出一个物理模型观测到的星星形成率（SFR）和分子线（CO和HCN）的星系发射之间的关系，并显示这些观测到的关系是如何反映的基本星星形成规律。我们这样做，通过结合3D非LTE辐射传输计算与孤立的盘星系和星系合并的流体动力学模拟。我们表明，所观察到的SFR分子线的关系是由分子线发射和气体密度之间的关系和锚定的指数的基本施密特定律控制的SFR在星系中。具有低临界密度的线（例如，CO J = 1-0）通常被热化并忠实地跟踪气体密度。在这些情况下，SFR将与具有类似于施密特定律指数的指数的线光度相关。具有高临界密度的线，其密度大于星系中大多数发射云的平均密度（例如，CO J = 3-2，HCN J = 1-0）将只有少量的热化气体，因此分子线光度（Lmol）与平均气体密度（）呈超线性关系。这导致SFR线光度指数小于高临界密度示踪剂的施密特指数。一个观测结果是，光从致密的小袋，热化气体的显着重新分布，扩散气体沿着视线，和巨大的发射从亚热激发气体。在最高的星星形成率，SFR-Lmol斜率倾向于施密特指数，无论分子的过渡。基本关系是Kennicutt-Schmidt定律，而不是SFR与分子线光度之间的关系。我们的模型为SFR分子线关系定量再现的斜率所观察到的SFR CO（J = 1-0），CO（J = 3-2），HCN（J = 1-0）的关系时，施密特定律与指数为1.5描述的SFR。我们使用这些结果，使迫在眉睫的可测试的预测SFR分子线关系的未观察到的过渡。
We derive a physical model for the observed relations between star formation rate (SFR) and molecular line (CO and HCN) emission in galaxies and show how these observed relations are reflective of the underlying star formation law. We do this by combining 3D non-LTE radiative transfer calculations with hydrodynamic simulations of isolated disk galaxies and galaxy mergers. We demonstrate that the observed SFR-molecular line relations are driven by the relationship between molecular line emission and gas density and anchored by the index of the underlying Schmidt law controlling the SFR in the galaxy. Lines with low critical densities (e.g., CO J = 1–0) are typically thermalized and trace the gas density faithfully. In these cases, the SFR will be related to line luminosity with an index similar to the Schmidt law index. Lines with high critical densities greater than the mean density of most of the emitting clouds in a galaxy (e.g., CO J = 3–2, HCN J = 1–0) will have only a small amount of thermalized gas and consequently a superlinear relationship between molecular line luminosity (Lmol) and mean gas density (). This results in an SFR-line luminosity index less than the Schmidt index for high critical density tracers. One observational consequence of this is a significant redistribution of light from the small pockets of dense, thermalized gas to diffuse gas along the line of sight, and prodigious emission from subthermally excited gas. At the highest star formation rates, the SFR-Lmol slope tends to the Schmidt index, regardless of the molecular transition. The fundamental relation is the Kennicutt-Schmidt law, rather than the relation between SFR and molecular line luminosity. Our model for SFR-molecular line relations quantitatively reproduces the slopes of the observed SFR-CO (J = 1–0), CO (J = 3–2), and HCN (J = 1–0) relations when a Schmidt law with index of ~1.5 describes the SFR. We use these results to make imminently testable predictions for the SFR-molecular line relations of unobserved transitions.