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The lifecycle of molecular clouds in nearby star-forming disc galaxies | | Mélanie Chevance
; J. M. Diederik Kruijssen
; Alexander P. S. Hygate
; Andreas Schruba
; Steven N. Longmore
; Brent Groves
; Jonathan D. Henshaw
; Cinthya N. Herrera
; Annie Hughes
; Sarah M. R. Jeffreson
; Philipp Lang
; Adam K. Leroy
; Sharon E. Meidt
; Jérôme Pety
; Alessandro Razza
; Erik Rosolowsky
; Eva Schinnerer
; Frank Bigiel
; Guillermo A. Blanc
; Eric Emsellem
; Christopher M. Faesi
; Simon C. O. Glover
; Daniel T. Haydon
; I-Ting Ho
; Kathryn Kreckel
; Janice C. Lee
; Daizhong Liu
; Miguel Querejeta
; Toshiki Saito
; Jiayi Sun
; Antonio Usero
; Dyas Utomo
; | | Date: |
8 Nov 2019 | | 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 $Sigma_{
m
H_2}geqslant8$M$_{odot}$pc$^{-2}$, the GMC lifetime correlates with
time-scales for galactic dynamical processes, whereas at $Sigma_{
m
H_2}leqslant8$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. | | Source: | arXiv, 1911.3479 | | Services: | Forum | Review | PDF | Favorites | |
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