Cloud structures in M 17 SWex : Possible cloud–cloud collision

Document Type


Department or Administrative Unit


Publication Date



Using wide-field 13CO (J = 1−0) data taken with the Nobeyama 45 m telescope, we investigate cloud structures of the infrared dark cloud complex in M 17 with Spectral Clustering for Interstellar Molecular Emission Segmentation. In total, we identified 118 clouds that include 11 large clouds with radii larger than 1 pc. The clouds are mainly distributed in the two representative velocity ranges of 10–20 km s−1 and 30–40 km s−1. By comparing this with the ATLASGAL catalog, we found that the majority of the 13CO clouds with 10–20 km s−1 and 30–40 km s−1 are likely located at distances of 2 kpc (Sagittarius arm) and 3 kpc (Scutum arm), respectively. Analyzing the spatial configuration of the identified clouds and their velocity structures, we attempt to reveal the origin of the cloud structure in this region. Here we discuss three possibilities: (1) overlapping with different velocities, (2) cloud oscillation, and (3) cloud–cloud collision. In the position–velocity diagrams, we found spatially extended faint emission between ∼20 km s−1 and ∼35 km s−1, which is mainly distributed in the spatially overlapped areas of the clouds. Additionally, the cloud complex system is unlikely to be gravitationally bound. We also found that in some areas where clouds with different velocities overlapped, the magnetic field orientation changes abruptly. The distribution of the diffuse emission in the position–position–velocity space and the bending magnetic fields appear to favor the cloud–cloud collision scenario compared to other scenarios. In the cloud–cloud collision scenario, we propose that two ∼35 km s−1 foreground clouds are colliding with clouds at ∼20 km s−1 with a relative velocity of 15 km s−1. These clouds may be substructures of two larger clouds having velocities of ∼35 km s−1 (≳103M) and ∼20 km s−1 (≳104M), respectively.


The download link on this page is to an accepted manuscript version of this article hosted by arXiv.org and may not be the final version of this article.

This article was originally published in Publications of the Astronomical Society of Japan. The full-text article from the publisher can be found here.

Due to copyright restrictions, this article is not available for free download from ScholarWorks @ CWU.


Publications of the Astronomical Society of Japan


© The Author(s) 2020. Published by Oxford University Press on behalf of the Astronomical Society of Japan.