The youngest known Galactic supernova remnant (SNR) G1.9+0.3 has high-velocity supernova shock beyond 10000 km s−1, and it is considered to be one of the major candidates of a PeVatron. Despite these outstanding properties, the surrounding interstellar matter of this object is poorly understood. We investigated the interstellar gas toward G1.9+0.3 using the 12CO(J = 3−2) data with the angular resolution of 15″ obtained by the CHIMPS2 survey by the James Clerk Maxwell Telescope, and discovered three individual clouds at −1, 7, and 45 km s−1. From its morphological and velocity structures, the −1 km s−1 cloud, having the largest velocity width >20 km s−1 and located at the distance of the Galactic Center, is possibly associated with the SNR. The associated cloud shows a cavity structure both in space and velocity and coincides well with the SNR. We found that the associated cloud has higher column densities toward three bright, radio synchrotron-emitted rims where the radial expansion velocity of the supernova shock is decelerated, and the cloud is faint in the other parts of the SNR. This is the first direct evidence indicating that the highly anisotropic expansion of G1.9+0.3 observed by previous studies results from the deceleration by the interaction between the supernova shock and surrounding dense interstellar medium.

中文翻译：

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发现可能与最年轻的银河信噪比 G1.9+0.3 有关的分子云

已知最年轻的银河超新星遗迹（SNR）G1.9+0.3具有超过10000 km s−1的高速超新星激波，它被认为是PeVatron的主要候选者之一。尽管具有这些突出的特性，但人们对该物体周围的星际物质知之甚少。我们利用詹姆斯·克拉克·麦克斯韦望远镜CHIMPS2巡天获得的角分辨率为15英寸的12CO(J = 3−2)数据对G1.9+0.3方向的星际气体进行了研究，并在-1处发现了三个独立的云， 7、45 km s−1。从其形态和速度结构来看，最大速度宽度>20 km s-1且位于银心距离的-1 km s-1云可能与SNR有关。相关的云在空间和速度上都显示出空腔结构，并且与信噪比很好地吻合。我们发现相关云在三个明亮的射电同步加速器发射边缘处具有较高的柱密度，在这些边缘处超新星激波的径向膨胀速度减慢，并且云在信噪比的其他部分中是微弱的。这是第一个直接证据表明，先前研究观测到的G1.9+0.3的高度各向异性膨胀是超新星激波与周围致密星际介质相互作用减速的结果。