Evolution of dust in the Orion Bar with Herschel I. Radiative transfer modelling
Evolution of dust in the Orion Bar with Herschel I. Radiative transfer modelling
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DOI：
10.1051/0004-6361/201118537
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发表时间：
2012-05-01
影响因子：
6.5
通讯作者：
White, G. J.
中科院分区：
文献类型：
--
作者：
Arab, H.;Abergel, A.;White, G. J.
上下文星际尘埃是我们理解星际介质和星星形成的关键因素。尘埃种群随激发和物理条件的演化方式是理解星际尘埃演化的第一步。在星际尘埃演化的赫歇尔关键计划的框架内，我们已经获得了PACS和SPIRE分光光度观测的各种光解区域，以验证这一演变。本文的目的是跟踪猎户座酒吧的光解离区的尘埃颗粒的演变。我们使用Herschel/PACS（70和160亩米）和SPIRE（250，350和500亩米）与斯皮策/IRAC的意见，映射的空间分布的尘埃种群酒吧。使用DustEM模型结合辐射传输程序模拟亮度分布。多亏了Herschel，我们能够以5.6 "到35.1“的分辨率详细探测猎户座棒致密部分的尘埃排放。这些新的观测结果使我们能够推断出棒中不同位置最大颗粒的温度，这揭示了从70 K到35 K的梯度，以及从电离锋到尘埃区的光谱发射率指数的增加。结合Spitzer/IRAC观测，这对来自表面的尘埃发射敏感，Herschel地图，我们能够测量猎户座棒从3.6到500 μ m的辐射。我们发现在不同的尘埃成分中存在一个分层现象，这种分层现象可以用一个简单的辐射传输模型定量再现，而不需要考虑尘埃的演化（星际介质的扩散丰度和光学性质），但是需要考虑尘埃的演化来解释每个波段的亮度。多环芳烃（PAH）的丰度变化，或PAH丰度变化的组合与混凝引起的最大颗粒发射率的增强给出了良好的结果。另一个假设是考虑电离前沿与非电离部分沿视线沿着的杆的长度不同。
Context. Interstellar dust is a key element in our understanding of the interstellar medium and star formation. The manner in which dust populations evolve with the excitation and the physical conditions is a first step in comprehending the evolution of interstellar dust.Aims. Within the framework of the Evolution of interstellar dust Herschel key programme, we have acquired PACS and SPIRE spectrophotometric observations of various photodissociation regions, to characterise this evolution. The aim of this paper is to trace the evolution of dust grains in the Orion Bar photodissociation region.Methods. We used Herschel/PACS (70 and 160 mu m) and SPIRE (250, 350 and 500 mu m) together with Spitzer/IRAC observations to map the spatial distribution of the dust populations across the Bar. Brightness profiles were modelled using the DustEM model coupled with a radiative transfer code.Results. Thanks to Herschel, we are able to probe in great detail the dust emission of the densest parts of the Orion Bar with a resolution from 5.6 '' to 35.1 ''. These new observations allow us to infer the temperature of the biggest grains at different positions in the Bar, which reveals a gradient from similar to 70 K to 35 K coupled with an increase of the spectral emissivity index from the ionization front to the densest regions.Combining Spitzer/IRAC observations, which are sensitive to the dust emission from the surface, with Herschel maps, we were able to measure the Orion Bar emission from 3.6 to 500 mu m. We find a stratification in the different dust components that can be quantitatively reproduced by a simple radiative transfer model without dust evolution (diffuse interstellar medium abundances and optical properties).However, including dust evolution is needed to explain the brightness in each band. Polycyclic aromatic hydrocarbon (PAH) abundance variations, or a combination of PAH abundance variations with an enhancement of the biggest grain emissivity caused by coagulation give good results. Another hypothesis is to consider a length of the Bar along the line of sight different at the ionization front than in the densest parts.