University of Hertfordshire

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From the same journal

By the same authors

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

Research output: Contribution to journalArticle

Documents

  • J.~D. Henshaw
  • S.~N. Longmore
  • J.~M.~D. Kruijssen
  • B. Davies
  • J. Bally
  • A. Barnes
  • C. Battersby
  • M.~R. Cunningham
  • A. Ginsburg
  • K. Immer
  • P.~A. Jones
  • S. Kendrew
  • E.~A.~C. Mills
  • S. Molinari
  • T.~J.~T. Moore
  • J. Ott
  • T. Pillai
  • J. Rathborne
  • P. Schilke
  • A. Schmiedeke
  • L. Testi
  • D. Walker
  • A. Walsh
  • Q. Zhang
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Original languageEnglish
Pages (from-to)2675-2702
Number of pages28
JournalMonthly Notices of the Royal Astronomical Society
Volume457
Issue3
DOIs
Publication statusPublished - 12 Feb 2016

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, vLSR} distribution of Central Molecular Zone (CMZ) gas, which is asymmetric about Sgr A* in both position and velocity. Velocity dispersions range from 2.6 km s−1 < σ < 53.1 km s−1. A median dispersion of 9.8 km s−1, translates to a Mach number, M3D≥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−1 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, vLSR} 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 3D 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 parametrization 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−1 and 50 km s−1 clouds and Sgr C.

Notes

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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