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Dense molecular gas properties on 100 pc scales across the disc of NGC 3627




Beslic, Ivana
Barnes, A T
Bigiel, Frank
Puschnig, J
Pety, Jerome
Herrera Contreras, C
Leroy, Adam K
Usero, Antonio
Schinnerer, E
Meidt, Sharon E

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Oxford University Press


It is still poorly constrained how the densest phase of the interstellar medium varies across galactic environment. A large observing time is required to recover significant emission from dense molecular gas at high spatial resolution, and to cover a large dynamic range of extragalactic disc environments. We present new NOrthern Extended Millimeter Array (NOEMA) observations of a range of high critical density molecular tracers (HCN, HNC, HCO+) and CO isotopologues ((CO)-C-13, (CO)-O-18) towards the nearby (11.3 Mpc) strongly barred galaxy NGC 3627. These observations represent the current highest angular resolution (1.85 arcsec; 100 pc) map of dense gas tracers across a disc of a nearby spiral galaxy, which we use here to assess the properties of the dense molecular gas, and their variation as a function of galactocentric radius, molecular gas, and star formation. We find that the HCN(1-0)/CO(2-1) integrated intensity ratio does not correlate with the amount of recent star formation. Instead, the HCN(1-0)/CO(2-1) ratio depends on the galactic environment, with differences between the galaxy centre, bar, and bar-end regions. The dense gas in the central 600 pc appears to produce stars less efficiently despite containing a higher fraction of dense molecular gas than the bar ends where the star formation is enhanced. In assessing the dynamics of the dense gas, we find the HCN(1-0) and HCO+(1-0) emission lines showing multiple components towards regions in the bar ends that correspond to previously identified features in CO emission. These features are cospatial with peaks of H alpha emission, which highlights that the complex dynamics of this bar-end region could be linked to local enhancements in the star formation.



stars: formation, ISM: clouds, ISM: molecules, galaxies: evolution, galaxies: ISM, galaxies: star formation



Monthly Notices of the Royal Astronomical Society


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Open Access

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