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Chevance, M, Kruijssen, JMD, Hygate, APS, Schruba, A, Longmore, SN, Groves, B, Henshaw, JD, Herrera, CN, Hughes, A, Jeffreson, SMR, Lang, P, Leroy, AK, Meidt, SE, Pety, J, Razza, A, Rosolowsky, E, Schinnerer, E, Bigiel, F, Blanc, GA, Emsellem, E , Faesi, CM, Glover, SCO, Haydon, DT, Ho, I-T, Kreckel, K, Lee, JC, Liu, D, Querejeta, M, Saito, T, Sun, J, Usero, A and Utomo, D (2019) The lifecycle of molecular clouds in nearby star-forming disc galaxies. Monthly Notices of the Royal Astronomical Society, 493 (2). pp. 2872-2909. ISSN 0035-8711
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Abstract
It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially-resolved ($\sim100$ pc) CO-to-H$\alpha$ flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically 10-30 Myr, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma_{\rm H_2}\geqslant8$M$_{\odot}$pc$^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma_{\rm H_2}\leqslant8$M$_{\odot}$pc$^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H$\alpha$ (75-90% of the cloud lifetime), GMCs disperse within just 1-5 Myr once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4-10% These results show that galactic star formation is governed by cloud-scale, environmentally-dependent, dynamical processes driving rapid evolutionary cycling. GMCs and HII regions are the fundamental units undergoing these lifecycles, with mean separations of 100-300 pc in star-forming discs. Future work should characterise the multi-scale physics and mass flows driving these lifecycles.
| Item Type: | Article |
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| Additional Information: | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| Uncontrolled Keywords: | astro-ph.GA; astro-ph.GA |
| Subjects: | Q Science > QB Astronomy |
| Divisions: | Astrophysics Research Institute |
| Publisher: | Oxford University Press |
| Related URLs: | |
| Date Deposited: | 25 Nov 2020 10:42 |
| Last Modified: | 04 Sep 2021 08:22 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/11811 |
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