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Molecular gas kinematics within the central 250 pc of the Milky Way

Henshaw, JD and Longmore, SN and Kruijssen, JMD and Davies, B and Bally, J and Barnes, AT and Battersby, C and Burton, M and Cunningham, MR and Dale, JE and Ginsburg, A and Immer, K and Jones, PA and Kendrew, S and Mills, EAC and Molinari, S and Moore, TJT and Ott, J and Pillai, T and Rathborne, J and Schilke, P and Schmiedeke, A and Testi, L and Walker, DL and Walsh, A and Zhang, Q (2016) Molecular gas kinematics within the central 250 pc of the Milky Way. Monthly Notices of the Royal Astronomical Society, 457 (3). pp. 2675-2702. ISSN 0035-8711

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Abstract

Using spectral-line observations of HNCO, N2H+, and HNC, we investigate the kinematics of dense gas in the central ~250 pc of the Galaxy. We present SCOUSE (Semi-automated multi-COmponent Universal Spectral-line fitting Engine), a line fitting algorithm designed to analyse large volumes of spectral-line data efficiently and systematically. Unlike techniques which do not account for complex line profiles, SCOUSE accurately describes the {l, b, v_LSR} distribution of CMZ gas, which is asymmetric about Sgr A* in both position and velocity. Velocity dispersions range from 2.6 km/s<\sigma<53.1 km/s. A median dispersion of 9.8 km/s, translates to a Mach number, M_3D>28. The gas is distributed throughout several "streams", with projected lengths ~100-250 pc. We link the streams to individual clouds and sub-regions, including Sgr C, the 20 and 50 km/s clouds, the dust ridge, and Sgr B2. Shell-like emission features can be explained by the projection of independent molecular clouds in Sgr C and the newly identified conical profile of Sgr B2 in {l ,b, v_LSR} space. These features have previously invoked supernova-driven shells and cloud-cloud collisions as explanations. We instead caution against structure identification in velocity-integrated emission maps. Three geometries describing the 3-D structure of the CMZ are investigated: i) two spiral arms; ii) a closed elliptical orbit; iii) an open stream. While two spiral arms and an open stream qualitatively reproduce the gas distribution, the most recent parameterisation of the closed elliptical orbit does not. Finally, we discuss how proper motion measurements of masers can distinguish between these geometries, and suggest that this effort should be focused on the 20 km/s and 50 km/s clouds and Sgr C.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record "Molecular gas kinematics within the central 250 pc of the Milky Way" is available online at: http://dx.doi.org/10.1093/mnras/stw121
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 21 Jan 2016 10:04
Last Modified: 31 Mar 2016 10:20
DOI or Identification number: 10.1093/mnras/stw121
URI: http://researchonline.ljmu.ac.uk/id/eprint/2725

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