隐埋星系核的温室效应与HCN共振振动辐射
The Greenhouse Effect in Buried Galactic Nuclei and the Resonant HCN Vibrational Emission
摘要：
最近的干涉观测表明，明亮的HCN发射从nu 2 =1振动状态中产生的掩埋核区域的星系，表明nu 2 =1状态通过吸收14 $μ$ m连续光子的有效泵浦。我们已经模拟了连续和HCN振动线发射在这些地区，其特点是高柱密度的尘埃和高光度，与球对称的方法，模拟一个中心热源（AGN）和紧凑的核星爆（SB）。我们发现，当H2柱变得非常高时，N_{H2} >~10^{25} cm-2，连续光子在核区域内的捕获显著提高了内部区域的尘埃温度（Tdust），即使从外部看到的预测光谱能量分布变得相对较冷。因此，该模型预测，在毫米波长下，亮度表面亮度（在模型源上的平均值）约为10^{8} Lsun pc^{-2}。这种{ \it温室}效应显著增强了尘埃体积内的平均中红外强度，使nu 2 =1状态达到HCN振动谱线变得光学厚的程度。活动星系核模型在内部区域产生更高的Tdust和更高的峰值（亚）毫米连续亮度比SB模型，但类似的HCN振动J=3-2和4-3的发射，由于光学深度效应和高\tdust \对这些低J线的适度影响。在几个星系中观测到的HCN振动发射可以用HCN丰度~10^{-6}（相对于H2）和光度表面亮度在（0.5-2）x10^{8}$ Lsun pc^{-2}范围内来解释，预测远红外光球的Tdust为~80-150 K --与从远红外分子吸收推断的值一致。
英文摘要：
Recent interferometric observations have shown bright HCN emission from the nu2=1 vibrational state arising in buried nuclear regions of galaxies, indicating an efficient pumping of the nu2=1 state through absorption of 14 $μ$m continuum photons. We have modeled the continuum and HCN vibrational line emission in these regions, characterized by high column densities of dust and high luminosities, with a spherically symmetric approach, simulating both a central heating source (AGN) and a compact nuclear starburst (SB). We find that when the H2 columns become very high, N_{H2}>~10^{25} cm-2, trapping of continuum photons within the nuclear region dramatically enhances the dust temperature (Tdust) in the inner regions, even though the predicted spectral energy distribution as seen from outside becomes relatively cold. The models thus predict bright continuum at millimeter wavelengths for luminosity surface brightness (averaged over the model source) of ~10^{8} Lsun pc^{-2}. This {\it greenhouse} effect significantly enhances the mean mid-infrared intensity within the dusty volume, populating the nu2=1 state to the extent that the HCN vibrational lines become optically thick. AGN models yield higher Tdust in the inner regions and higher peak (sub)millimeter continuum brightness than SB models, but similar HCN vibrational J=3-2 and 4-3 emission owing to both optical depth effects and a moderate impact of high \tdust\ on these low-J lines. The observed HCN vibrational emission in several galaxies can be accounted for with a HCN abundance of ~10^{-6} (relative to H2) and luminosity surface brightness in the range (0.5-2)x10^{8}$ Lsun pc^{-2}, predicting a far-infrared photosphere with Tdust}~80-150 K --in agreement with the values inferred from far-infrared molecular absorption.
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