The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3
The molecular clouds in the environs of the supernova remnants G349.7+0.2 and G18.8+0.3
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DOI：
10.1051/0004-6361:20041327
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发表时间：
2004-10
影响因子：
6.5
通讯作者：
G. Dubner;E. Giacani;E. Reynoso;S. Paron
中科院分区：
文献类型：
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作者：
G. Dubner;E. Giacani;E. Reynoso;S. Paron
我们展示了与超新星遗迹 (SNR) G349.7+0.2 和 G18.8+0.3 相关的分子气体的新高分辨率研究结果。使用 SEST 望远镜在 12 CO J = 1-0、2-1 和 3-2 线（光束分别为 45、23 和 15）进行观测。目前的观测结果为这两个信噪比提供了新的证据，支持SN激波与相邻分子云之间存在物理相互作用。以G349.7+0.2为例，新的观测结果首次揭示了激波云的内部结构，以及SNR激波对分子云影响的运动学后果。根据这些观察，我们能够限制预激气体的条件。与 G349.7+0.2 相关的分子云，中心位于 ν LSR = +16.2 km s -1 附近，线性尺寸约为 7 pc，质量约为 ∼10 4 M ○。体积密度～10 3 cm -3 。得出的高线比表明云中存在激波。根据线形状中观察到的不对称性，我们认为超新星激波云正在进入云层较密的部分，并且可能已经开始扰乱它，将东部的团块推离我们，而将西部的碎片推向我们。将我们对介入气体柱密度的估计与基于 ASCA X 射线光谱拟合的类似计算进行比较后，我们得出结论，使这些结果兼容的最佳方法是假设相关云沿视线放置在 G349.7+0.2 后面，并且 SNR/分子云相遇发生在 SNR 的远端。该模型还为 G349.7+0.2 中心区域缺乏强 X 射线吸收提供了自然的解释。部分相关云的蒸发一定是中央 X 射线发射的原因。与 IRAS 红外数据的比较为 SNR/云物理相互作用的假设提供了额外的支持。通过对 G349.7+0.2 中检测到的五个 OH (1720 MHz) 脉泽附近的分子气体的研究，我们发现在三种情况下，脉泽峰值速度与局部 CO 峰值速度一致，而在其余两种情况下，脉泽峰值速度与次级混合 CO 分量一致。我们得出的结论是，微波激射器在局部横向于视线（或与视线形成大角度）的非解离 C 型激波撞击更密集的分子团的位置处被激发。对于 SNR G18.8+0.3，新的更高分辨率的观测结果显示云成分之一与朝向东缘的 SNR 激波锋面之间具有极好的形态一致性。相关分子质量估计为∼4.4 x 10 4 M ○。云体积密度～1200 cm -3 。对这种情况下的线比的分析显示，在与残余物壳中无线电连续谱发射中的凹口完全匹配的位置处，最大值为 R 2-1/1-0 = 1.25，从而提供了 SNR/分子云相互作用的额外证据。
We present the results of a new high-resolution study of the molecular gas associated with the supernova remnants (SNRs) G349.7+0.2 and G18.8+0.3. The observations were performed with the SEST telescope in the 12 CO J = 1-0, 2-1 and 3-2 lines (beams of 45, 23 and 15, respectively). The present observations have provided, for the two SNRs, new evidence in support of the existence of physical interaction between the SN shocks and the adjoining molecular clouds. In the case of G349.7+0.2, the new observations revealed for the first time the internal structure of the shocked cloud, as well as the kinematical consequences of the impact of the SNR shock on the molecular cloud. From these observations we were able to constrain the conditions of the pre-shocked gas. The molecular cloud associated with G349.7+0.2, centered near ν LSR = +16.2 km s -1 , has a linear size of about 7 pc, a mass of ∼10 4 M ○. and a volume density of ∼10 3 cm -3 . The high line ratios derived are indicative of the existence of shocks in the cloud. From the asymmetries observed in the line shapes we propose that the SN shock cloud is running into the denser part of the cloud and has probably begun to disrupt it, pushing the eastern component clumps away from us, and the western fragments toward us. After comparing our estimates of the column density of the intervening gas with similar calculations based on ASCA X-rays spectral fitting we conclude that the best way to make these results compatible is by assuming that the associated cloud is placed behind G349.7+0.2 along the line of sight, and the SNR/molecular cloud encounter is taking place on the far side of the SNR. This model also provides a natural explanation for the lack of strong X-ray absorption in the central region of G349.7+0.2. Evaporation of part of the associated cloud must be responsible for the central X-ray emission. The comparison with IRAS infrared data provides additional support for the hypothesis of SNR/cloud physical interaction. From the study of the molecular gas in the neighborhood of the five OH (1720 MHz) masers detected in G349.7+0.2 we find that in three cases the maser peak velocity coincides with the local CO peak velocity, while in the remaining two cases the maser peak velocity agrees with a secondary, blended CO component. We conclude that the masers are excited at the sites where a non-dissociative C-type shock, locally transverse to the line of sight (or forming a large angle with it), hits a denser molecular clump. For the SNR G18.8+0.3, the new higher resolution observations have revealed excellent morphological agreement between one of the cloud components and the SNR shock front towards the eastern limb. The associated molecular mass is estimated to be ∼4.4 x 10 4 M ○. and the cloud volume density ∼1200 cm -3 . The analysis of the line ratios in this case revealed a maximum of R 2-1/1-0 = 1.25 at a position that exactly matches an indentation in the radio continuum emission in the remnant's shell, providing additional evidence of SNR/molecular cloud interaction.