Beslic, IvanaBarnes, A TBigiel, FrankPuschnig, JPety, JeromeHerrera Contreras, CLeroy, Adam KUsero, AntonioSchinnerer, EMeidt, Sharon EGrasha, Kathryn2023-09-142023-09-140035-8711http://hdl.handle.net/1885/299547It 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.This work is based on IRAM/NOEMA observations carried out under project number W17BP, and the EMPIRE large program number 206-14 with the IRAM 30-m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). IB, ATB, FB, JPu, and JSdB would like to acknowledge the funding provided from the European Union’s Horizon 2020 Framework Programme (grant agreement no. 726384/Empire). CE acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG) Sachbeihilfe, grant number BI1546/3-1. JPe and CHC acknowledge support by the Programme National ‘Physique et Chimie du Milieu Interstellaire’ (PCMI) of CNRS/INSU with INC/INP, cofunded by CEA and CNES. The work of AKL is partially supported by the National Science Foundation under grants no. 1615105, 1615109, and 1653300. AU acknowledges support from the Spanish funding grants PGC2018- 094671-B-I00 (MCIU/AEI/FEDER) and PID2019-108765GB-I00 (MICINN). ES, DL, IP, TS, and FS acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme (grant agreement no. 694343). AH was supported by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, cofunded by CEA and CNES, and by the Programme National ‘Physique et Chimie du Milieu Interstellaire’ (PCMI) of CNRS/INSU with INC/INP cofunded by CEA and CNES. CF is supported by the National Science Foundation under Award No. 1903946 and acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme (grant agreement no. 694343). KK gratefully acknowledges funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group (grant number KR4598/2-1, PI: Kreckel). MC and JMDK gratefully acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through an Emmy Noether Research Group (grant number KR4801/1-1) and the DFG Sachbeihilfe (grant number KR4801/2-1), and from the European Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). SCOG, RSK, and MCS acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center (SFB 881, Project-ID 138713538) ‘The Milky Way System’ (subprojects A1, B1, B2, and B8) and from the Heidelberg cluster of excellence (EXC 2181 - 390900948) ‘STRUCTURES: A unifying approach to emergent phenomena in the physical world, mathematics, and complex data’, funded by the German Excellence Strategy. RSK also thanks for funding form the European Research Council in the ERC Synergy Grant ‘ECOGAL – Understanding our Galactic ecosystem: From the disk of the Milky Way to the formation sites of stars and planets’ (project ID 855130). ER acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference number RGPIN-2017-03987. MCS acknowledges financial support from the German Research Foundation (DFG) via the Collaborative Research Centre (SFB 881, Project-ID 138713538) ‘The Milky Way System’ (subprojects A1, B1, B2, and B8). MQ acknowledges support from the research project PID2019-106027GA-C44 from the Spanish Ministerio de Ciencia e Innovacion. TGW acknowledges funding from the European ´ Research Council (ERC) under the European Union’s Horizon 2020 Framework Programme (grant agreement no. 694343)application/pdfen-AU© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Societystars: formationISM: cloudsISM: moleculesgalaxies: evolutiongalaxies: ISMgalaxies: star formation202110.1093/mnras/stab17762022-07-31