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Title:
The large-scale atomic and molecular gas in the Circinus galaxy
Authors:
Curran, S. J.; Koribalski, B. S.; Bains, I.
Affiliation:
AA(School of Physics, University of New South Wales, Sydney, NSW 2052, Australia; Onsala Space Observatory, Chalmers University of Technology, S-439 92 Onsala, Sweden), AB(Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia), AC(Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 389, Issue 1, pp. 63-74. (MNRAS Homepage)
Publication Date:
09/2008
Origin:
MNRAS
MNRAS Keywords:
galaxies: active , galaxies: individual: Circinus , galaxies: ISM , galaxies: kinematics and dynamics , galaxies: Seyfert , radio lines: galaxies
DOI:
10.1111/j.1365-2966.2008.13574.x
Bibliographic Code:
2008MNRAS.389...63C

Abstract

We have used the Australia Telescope Compact Array (ATCA) and the Swedish-ESO Submillimetre Telescope (SEST) to map the large-scale atomic and molecular gas in the nearby (4Mpc) Circinus galaxy. The ATCA HI mosaic of Circinus exhibits the warps in position angle and inclination revealed in the single-pointing image of Jones et al., both of which appear to settle beyond the inner 30kpc which was previously imaged. The molecular gas has been mapped in both the CO J = 1 -> 0 and J = 2 -> 1 transitions down to a column density of (3σ), where we derive a total molecular gas mass of . Within a radius of 3kpc, i.e. where CO was clearly detected, the molecular fraction climbs steeply from ~ 0.7 to unity (where , cf. NHI = 1021cm-2) with proximity to the nucleus. Our HI mosaic gives an atomic gas mass of MHI ~ 6 × 109Msolar, which is 70 per cent of the fully mapped single dish value. Combining the atomic and molecular gas masses gives a total gas mass of , cf. the total dynamical mass of ~ 3 × 1011Msolar within the inner 50kpc of our mosaiced image. The total neutral gas mass to dynamical mass ratio is therefore 3 per cent, consistent with the SAS3 (Third Small Astronomy Satellite) classification of Circinus. The high (molecular) gas mass fraction of per cent found by Curran et al., only occurs close to the central ~ 0.5kpc and falls to <~10 per cent within and outwith this region, allaying previous concerns regarding the validity of applying the Galactic conversion ratio to Circinus. The rotation curve, as traced by both the HI and CO, exhibits a steep dip at ~ 1kpc, the edge of the atomic/molecular ring, within which the starburst is occurring. We find the atomic and molecular gases to trace different kinematical features and believe that the fastest part (>~130kms-1) of the subkpc ring consists overwhelmingly of molecular gas. Beyond the inner kpc, the velocity climbs to settle into a solid body rotation of ~ 150kms-1 at >~10kpc. Most of the starlight emanates from within this radius and so much of the dynamical mass, which remains climbing to the limit of our data (>~50kpc), must be due to the dark matter halo.
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