Is the galactic submillimeter dust emissivity underestimated
Is the galactic submillimeter dust emissivity underestimated
复制标题
银河亚毫米尘埃发射率是否被低估
DOI：
10.1051/0004-6361:20042442
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发表时间：
2005
影响因子：
6.5
通讯作者：
N. Kylafis
中科院分区：
文献类型：
--
作者：
K. Dasyra;E. Xilouris;A. Misiriotis;N. Kylafis
我们提出了详细的光谱能量分布（SED）的旋涡星系NGC 891，NGC 4013和NGC 5907在远红外（FIR）和亚毫米（submm）波长的模型。该模型考虑到了辐射的扩散尘埃成分，这是由恒星产生的紫外线和光辐射场加热，以及发射本地产生的星星形成HII复合物。在光学波段的辐射传输模拟被用来约束恒星和尘埃的几何参数和尘埃质量。我们发现，我们的模型预测的submm发射不能解释在这些波长处观察到的通量。两种情况下，可以占“失踪”submm通量进行检查。在第一种情况下，除了来自光学波长的尘埃之外，尘埃以薄盘的形式嵌入星系中。这个额外的尘埃盘，这是无法检测到的光学和这是与年轻的恒星人口，引起额外的submm的排放，并使总流量与观测值相匹配。另一种情况是，在漫射成分和密度较高的环境（例如分子气体云）中发现的尘埃颗粒在亚毫米波长处的平均发射率高于银河系环境中广泛使用的值。这种增强的发射率再现所观察到的FIR和submm通量与尘埃质量等于来自光学观测。在第二种情况下，我们把submm发射率作为一个自由参数，并计算其标称值拟合我们的模型所观察到的SED。我们发现尘埃的发射率是我们银河系常用值的3倍。这两种情况都可以同样好地再现所有三个星系观测到的850 μ m表面亮度。然而，我们认为，有更多的尘埃嵌入在第二个磁盘的情况是不支持的近红外观测。在2.16 μ m处，带有第二个尘埃盘的模型图像显示了一个在观测中不存在的突出的尘埃带。因此，在亚毫米波段的发射率增强是一个真实的可能性和银河系的亚毫米尘埃发射率可能被低估。
We present detailed modeling of the spectral energy distribution (SED) of the spiral galaxies NGC 891, NGC 4013 and NGC 5907 in the far-infrared (FIR) and sub-millimeter (submm) wavelengths. The model takes into account the emission of the diffuse dust component, which is heated by the UV and optical radiation field produced by the stars, as well as the emission produced locally in star forming HII complexes. Radiative transfer simulations in the optical bands are used to constrain the stellar and dust geometrical parameters and the dust mass. We find that the submm emission predicted by our model cannot account for the observed fluxes at these wavelengths. Two scenarios that could account for the “missing” submm flux are examined. In the first scenario dust additional to that derived from the optical wavelengths is embedded in the galaxy in the form of a thin disk. This additional dust disk, which is not detectable in the optical and which is associated with the young stellar population, gives rise to additional submm emission, and makes the total flux match the observed values. The other scenario examines the possibility that the average emissivity at submm wavelengths of the dust grains found both in a diffuse component and in denser environments (e.g. molecular gas clouds) is higher than the values widely used in Galactic environments. This enhanced emissivity reproduces the observed FIR and submm fluxes with the dust mass equal to that derived from the optical observations. In the second scenario, we treat the submm emissivity as a free parameter and calculate its nominal value by fitting our model to the observed SED. We find a dust emissivity which is ~$ 3$ times the often-used values for our Galaxy. Both scenarios can equally well reproduce the observed 850 μ m surface brightness for all three galaxies. However, we argue that the scenario of having more dust embedded in a second disk is not supported by the near infrared observations. At 2.16 μ m, the model images with a second dust disk reveal a prominent dust lane which is not present in the observations. Thus, the enhanced emissivity at submm wavelengths is a real possibility and the Galactic submillimeter dust emissivity may be underestimated.