# Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback

Kruijssen, JMD, Schruba, A, Chevance, M, Longmore, SN, Hygate, APS, Haydon, DT, McLeod, AF, Dalcanton, JJ, Tacconi, LJ and Dishoeck, EFV (2019) Fast and inefficient star formation due to short-lived molecular clouds and rapid feedback. Nature, 569. pp. 519-522. ISSN 1476-4687

 Text 1905.08801v2.pdf - Accepted Version Restricted to Repository staff only until 22 November 2019. Download (7MB)

## Abstract

The physics of star formation and the deposition of mass, momentum, and energy into the interstellar medium by massive stars (`feedback') are the main uncertainties in modern cosmological simulations of galaxy formation and evolution. These processes determine the properties of galaxies, but are poorly understood on the $\lesssim$100 pc scale of individual giant molecular clouds (GMCs) resolved in modern galaxy formation simulations. The key question is why the timescale for depleting molecular gas through star formation in galaxies ($t_{\rm dep}\approx 2$ Gyr) exceeds the dynamical timescale of GMCs by two orders of magnitude. Either most of a GMC's mass is converted into stars over many dynamical times, or only a small fraction turns into stars before the GMC is dispersed on a dynamical timescale. Here we report our observation that molecular gas and star formation are spatially de-correlated on GMC scales in the nearby flocculent spiral galaxy NGC300, contrary to their tight correlation on galactic scales. We demonstrate that this de-correlation implies rapid evolutionary cycling between GMCs, star formation, and feedback. We apply a novel statistical method to quantify the evolutionary timeline and find that star formation is regulated by efficient stellar feedback, driving GMC dispersal on short timescales (~1.5 Myr) due to radiation and stellar winds, prior to supernova explosions. This feedback limits GMC lifetimes to about one dynamical timescale (~10 Myr), with integrated star formation efficiencies of only 2-3%. Our findings reveal that galaxies consist of building blocks undergoing vigorous, feedback-driven lifecycles, that vary with the galactic environment and collectively define how galaxies form stars. Systematic applications of this multi-scale analysis to large galaxy samples will provide key input for a predictive, bottom-up theory of galaxy formation and evolution.

Item Type: Article this is the authors' version before final edits; low-resolution versions of the Supplementary Videos are available as ancillary files in the arXiv source (see Author URL below), whereas the full-resolution versions are available with the Nature publication MD Multidisciplinary Q Science > QB Astronomy Astrophysics Research Institute Nature Research (part of Springer Nature) Author 24 May 2019 15:07 24 May 2019 15:15 10.1038/s41586-019-1194-3 http://researchonline.ljmu.ac.uk/id/eprint/10764

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