冲击气体对W28 gamma-ray源的氨激发成像HESS J1801-233
Ammonia excitation imaging of shocked gas towards the W28 gamma-ray source HESS J1801-233
摘要：
我们用12 mm的莫普拉望远镜观测了W28超新星遗迹（SNR）东北方向（NE）的致密（>10^3 cm^-3）分子气体。这个云在空间上与TeV伽马射线源HESS J1801-233匹配良好，并且已知是SNR-分子云相互作用区域。冲击破坏是明显的，从宽NH3（1，1）谱线宽度的区域对W28 SNR，而强烈的空间扩展NH3（3，3），NH3（4，4）和NH3（6，6）的反演发射到云的检测加强的情况下，存在高温的云。速度色散测量和NH3（n，n）/（1，1）比值图（n=2，3，4和6）表明，扰动源来自云最靠近W28 SNR的一侧，表明它是云扰动的源。对云的一部分，观察到的比例ortho对para-NH3超过2，这表明气相NH3富集由于NH3从尘埃颗粒地幔释放。测得的NH3相对于H2的丰度为~（1.2+/-0.5）*10^-9，这个值并不高，这可能与被升华的颗粒表面分子富集的热的、致密的分子云的丰度相同。结果表明，NH3升华和破坏的分子云，这可能是相互作用的W28 SNR冲击。
英文摘要：
We present 12 mm Mopra observations of the dense (>10^3 cm^-3 ) molecular gas towards the north-east (NE) of the W28 supernova remnant (SNR). This cloud is spatially well-matched to the TeV gamma-ray source HESS J1801-233 and is known to be a SNR-molecular cloud interaction region. Shock-disruption is evident from broad NH3 (1,1) spectral line-widths in regions towards the W28 SNR, while strong detections of spatially-extended NH3(3,3), NH3(4,4) and NH3(6,6) inversion emission towards the cloud strengthen the case for the existence of high temperatures within the cloud. Velocity dispersion measurements and NH3(n,n)/(1,1) ratio maps, where n=2, 3, 4 and 6, indicate that the source of disruption is from the side of the cloud nearest to the W28 SNR, suggesting that it is the source of cloud-disruption. Towards part of the cloud, the ratio of ortho to para-NH3 is observed to exceed 2, suggesting gas-phase NH3 enrichment due to NH3 liberation from dust grain mantles. The measured NH3 abundance with respect to H2 is ~(1.2+/-0.5)*10^-9, which is not high, as might be expected for a hot, dense molecular cloud enriched by sublimated grain-surface molecules. The results are suggestive of NH3 sublimation and destruction in this molecular cloud, which is likely to be interacting with the W28 SNR shock.
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