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arXiv 0712.1202astro-ph
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模拟ULIRGs II的光谱能量分布：高能环境和稠密的星际介质

Modelling the spectral energy distribution of ULIRGs II: The energetic environment and the dense interstellar medium

O. Vega, M. S. Clemens, A. Bressan, G. L. Granato, L. Silva, P. Panuzzo, --

备注：
Re-submitted to A&A
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摘要：

我们适合近红外无线电光谱的能量分布的30个发光和超亮红外星系与纯星爆模型或模型，包括星爆和活动星系核组件，以确定重要的物理参数，这个人口的对象。特别是，我们约束的光学深度对光度源，恒星形成率，恒星形成效率和活动星系核的分数。我们发现，虽然我们的样本中约有一半的最佳拟合模型，包括AGN组件，只有30%的AGN占红外光度的10%以上，而所有的积极占主导地位的星暴。我们推导出的活动星系核分数一般在很好的协议，其他测量的基础上，中红外线比测量斯皮策IRS，但低于PAH等效宽度或中红外光谱斜率。我们的模型通过重现SED所需的消光来确定致密分子气体的质量。假设这个质量是HCN示踪的质量，我们再现了高和所罗门发现的HCN和红外光度之间的线性关系。我们还发现，恒星形成效率，定义为当前的恒星形成率每单位的致密分子气体质量，是增强的ULIRGs阶段。如果ULIRGs的演化包括一个活动星系核对红外光度贡献很大的阶段，那么这个阶段的持续时间应该比星暴阶段短一个数量级。由于我们推导出的致密分子气体的质量与HCN分子的观测结果一致，因此当分子线数据不可用时，应该可以估计这些物体中致密的恒星形成分子气体的质量。

英文摘要：

We fit the near-infrared to radio spectral energy distributions of 30 luminous and ultra-luminous infrared galaxies with pure starburst models or models that include both starburst and AGN components to determine important physical parameters for this population of objects. In particular we constrain the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and the AGN fraction. We find that although about half of our sample have best-fit models that include an AGN component, only 30% have an AGN which accounts for more than 10% of the infrared luminosity, whereas all have an energetically dominant starburst. Our derived AGN fractions are generally in good agreement other measurements based in the mid-infrared line ratios measured by Spitzer IRS, but lower than those derived from PAH equivalent widths or the mid-infrared spectral slope. Our models determine the mass of dense molecular gas via the extinction required to reproduce the SED. Assuming that this mass is that traced by HCN, we reproduce the observed linear relation between HCN and infrared luminosities found by Gao & Solomon. We also find that the star formation efficiency, defined as the current star formation rate per unit of dense molecular gas mass, is enhanced in the ULIRGs phase. If the evolution of ULIRGs includes a phase in which an AGN contributes an important fraction to the infrared luminosity, this phase should last an order of magnitude less time than the starburst phase. Because the mass of dense molecular gas which we derive is consistent with observations of the HCN molecule,it should be possible to estimate the mass of dense, star-forming molecular gas in such objects when molecular line data are not available.

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