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arXiv 1401.6899astro-ph.GA
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局部ISM三维分布和软X射线背景:对附近热气体和北极支线的推断

Local ISM 3D distribution and soft X-ray background: Inferences on nearby hot gas and the North Polar Spur

L. Puspitarini, R. Lallement, J. L. Vergely, S. L. Snowden

摘要:

ISM的3D地图不仅可以用来定位IS云,还可以定位由恒星风和超新星吹来的云之间的IS气泡。我们比较我们的3D地图的IS灰尘的ROSAT弥漫X射线背景图。在平面中,在映射的附近空腔的位置和范围与0.25 keV背景发射分布之间存在良好的对应关系,表明这些附近空腔中的大多数有助于这种软X射线发射。假设一个恒定的尘埃与气体的比例和均匀的1 MK热气体填充的空腔,我们在一个简单的方式沿银河系平面从太阳看到的0.25 keV的表面亮度建模,考虑到吸收映射的云。数据-模型比较支持局部气泡(LB)中存在热气体。发现局部空腔中的平均压力约为10,000 cm-3 K,与以前的研究一致。该模型高估了第三象限中巨大空洞的辐射。使用CaII吸收数据,我们表明,灰尘CaII的比例是非常小的,在这个区域,这意味着存在大量的较低温度(非X射线发射)电离气体,解释至少部分的差异。在子午面,两个主要的亮度增强与连接LB和晕的烟囱吻合得很好。在高纬度明亮的北极脊附近没有发现空洞。我们在地图中搜索第4和第1象限中0.75 keV增强的源区。隧道和空洞被发现与主要的明亮区域相吻合,但是没有隧道或空洞被发现与低纬度,最明亮的部分相匹配。此外,地图和公布的光谱之间的比较不赞成附近的空腔位于约200 pc作为潜在的源区的太阳能电池。

英文摘要:

3D maps of the ISM can be used to locate not only IS clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae. We compare our 3D maps of the IS dust to the ROSAT diffuse X-ray background maps. In the Plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the 0.25 keV background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 1MK hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the Local Bubble (LB). The average mean pressure in the local cavities is found to be on the order of about 10,000 cm-3K, in agreement with previous studies. The model overestimates the emission from the huge cavities in the 3rd quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in this region, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the chimneys connecting the LB to the halo. No nearby cavity is found towards the bright North Polar Spur (NPS) at high latitude. We searched in the maps for the source regions of the 0.75 keV enhancements in the 4th and 1st quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude, brightest part of the NPS. In addition, the comparison between the maps and published spectra do not favor the nearby cavities located within about 200pc as potential source regions for the NPS.

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