Dust emissivity variations in the Milky Way
Dust emissivity variations in the Milky Way
复制标题
银河系中尘埃发射率的变化
DOI：
10.1051/0004-6361/200811246
复制
发表时间：
2009
影响因子：
6.5
通讯作者：
C. Meny
中科院分区：
文献类型：
--
作者：
D. Paradis;J. Bernard;C. Meny
目标。尘埃的性质似乎因尘埃形成的环境而异。以前的观测表明，这些变化在远红外（FIR）和亚毫米（submm）光谱范围是稀缺的，并限于特定区域的天空。为了确定这些结果是否可以推广到更大的尺度，我们研究了尘埃发射率的演变，从FIR到毫米（mm）波长，在原子和分子星际介质（ISM），沿着银河系平面朝向外星系。
方法.我们关联的尘埃FIR毫米发射与HI和CO发射，这是采取跟踪原子和分子相，分别。利用DIRBE 100 ~ 240 μm、Archeops 550 ~ 2.1mm和WMAP 3.2mm（W波段）的数据，在银河系纬度范围内进行了研究|B| ≤ 30°，在Archeops观测到的银河经度范围内（75° < l < 198°）。我们估计在每个阶段的平均尘埃温度，并划分的发射光谱能量分布（SED）的黑体在这个温度下推导出的发射率分布。提供了隐含简化影响的详细验证，例如沿视线沿着的温度混合。
结果在所研究的所有区域中，原子和分子相的发射率谱在FIR（β = 2.4）中比在submm和mm（β = 1.5）中更陡。我们发现显着的变化，作为一个函数的尘埃温度在分子阶段的尘埃发射率的光谱形状。在分子和原子气体中，尘埃温度相似的区域表现出相似的发射率光谱。尘埃在分子阶段温度明显较低的区域，在100-550 μm范围内的发射率显着增加。我们排除了这种效应是我们温度测定或假设的人为产物的可能性。这一结果支持了在这些地区的颗粒凝结的假设，证实了在以前的研究中获得的结果，并允许我们将这些结果扩展到外部MW的一般冷分子环境。所观察到的发射率增加的分子阶段，消失在毫米范围内的可能原因进行了讨论，通过比较与灰尘模型，涉及灰尘聚集和固态物理过程特定的非晶材料。我们注意到，这是第一次，这些影响已经证明了直接测量的发射率，而以前的研究仅基于热参数。
Aims. Dust properties appear to vary according to the environment in which the dust evolves. Previous observational indications of these variations in the far-infrared (FIR) and submillimeter (submm) spectral range are scarce and limited to specific regions of the sky. To determine whether these results can be generalised to larger scales, we study the evolution in dust emissivities from the FIR to millimeter (mm) wavelengths, in the atomic and molecular interstellar medium (ISM), along the Galactic plane towards the outer Galaxy.
Methods. We correlate the dust FIR to mm emission with the HI and CO emission, which are taken to trace the atomic and molecular phases, respectively. The study is carried out using the DIRBE data from 100 to 240 μm, the Archeops data from 550 μm to 2.1 mm, and the WMAP data at 3.2 mm (W band), in regions with Galactic latitude |b| ≤ 30°, over the Galactic longitude range (75° < l < 198°) observed with Archeops. We estimate the average dust temperature in each phase and divide the emission spectral energy distribution (SED) by a black body at this temperature to derive the emissivity profile. A detailed verification of the impact of the implied simplification, such as temperature mixing along the line of sight, is provided.
Results. In all regions studied, the emissivity spectra in both the atomic and molecular phases are steeper in the FIR (β = 2.4) than in the submm and mm (β = 1.5). We find significant variations in the spectral shape of the dust emissivity as a function of the dust temperature in the molecular phase. Regions of similar dust temperature in the molecular and atomic gas exhibit similar emissivity spectra. Regions where the dust is significantly colder in the molecular phase show a significant increase in emissivity for the range 100–550 μm. We exclude the possibility of this effect being an artifact of our temperature determination or the assumptions made. This result supports the hypothesis of grain coagulation in these regions, confirming results obtained over small fractions of the sky in previous studies and allowing us to expand these results to the cold molecular environments in general of the outer MW. Possible reasons for the observed emissivity increase in the molecular phase that vanishes in the mm range are discussed by comparison with dust models, involving dust aggregation and solid state physics processes specific to amorphous material. We note that it is the first time that these effects have been demonstrated by direct measurement of the emissivity, while previous studies were based only on thermal arguments.