Streaming motions and kinematic distances to molecular clouds
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We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of vR ≈ -9 km s-1 and rotate approximate to 6 km s-1 slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is ≈ 3 per cent of the disc potential in our model. We compare the actual distance and the kinematic estimate and we find that streaming motions introduce systematic offsets of ≈ 1 kpc. We find that the distance error can be as large as ± 2 kpc, and the recovered cloud positions have distributions that can extend significantly into the inter-arm regions. We conclude that this poses a difficulty in tracing spiral arm structure in molecular cloud surveys.
Fox , F G R & Bonnell , I A 2018 , ' Streaming motions and kinematic distances to molecular clouds ' Monthly Notices of the Royal Astronomical Society , vol 474 , no. 2 , pp. 2028-2038 . DOI: 10.1093/mnras/stx2866
Monthly Notices of the Royal Astronomical Society
© 2017 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1093/mnras/stx2866
FGR-F and IAB gratefully acknowledge support from the ERC Advanced Grant ECOGAL project, grant agreement 291227, funded by the European Research Council under ERC-2011-ADG.
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