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WISDOM Project – XV. giant molecular clouds in the central region of the barred spiral galaxy NGC 5806

Choi, Woorak, Liu, Lijie, Bureau, Martin, Cappellari, Michele, Davis, Timothy A. ORCID:, Gensior, Jindra, Liang, Fu-Heng, Lu, Anan, Williams, Thomas G. and Chung, Aeree 2023. WISDOM Project – XV. giant molecular clouds in the central region of the barred spiral galaxy NGC 5806. Monthly Notices of the Royal Astronomical Society 522 (3) , 4078–4097. 10.1093/mnras/stad1211

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We present high spatial resolution (≈24 pc) Atacama Large Millimeter/sub-millimeter Array 12CO(2-1) observations of the central region of the nearby barred spiral galaxy NGC 5806. NGC 5806 has a highly structured molecular gas distribution with a clear nucleus, a nuclear ring, and offset dust lanes. We identify 170 spatially and spectrally resolved giant molecular clouds (GMCs). These clouds have comparable sizes (Rc) and larger gas masses, observed linewidths (σobs, los), and gas mass surface densities than those of clouds in the Milky Way disc. The size–linewidth relation of the clouds is one of the steepest reported so far (⁠σobs,los∝R1.20c ), the clouds are on average only marginally bound (with a mean virial parameter 〈αvir〉 ≈ 2), and high velocity dispersions are observed in the nuclear ring. These behaviours are likely due to bar-driven gas shocks and inflows along the offset dust lanes, and we infer an inflow velocity of ≈120 km s−1 and a total molecular gas mass inflow rate of ≈5 M⊙ yr−1 into the nuclear ring. The observed internal velocity gradients of the clouds are consistent with internal turbulence. The number of clouds in the nuclear ring decreases with azimuthal angle downstream from the dust lanes without clear variation of cloud properties. This is likely due to the estimated short lifetime of the clouds (≈6 Myr), which appears to be mainly regulated by cloud–cloud collision and/or shear processes. Overall, it thus seems that the presence of the large-scale bar and gas inflows to the centre of NGC 5806 affect cloud properties.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 1365-2966
Date of First Compliant Deposit: 15 September 2023
Date of Acceptance: 20 April 2023
Last Modified: 19 Sep 2023 02:01

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