STAR FORMATION EFFICIENCIES AND LIFETIMES OF GIANT MOLECULAR CLOUDS IN THE MILKY WAY

By N. Murray. 2010

287 citations recorded by the source corpus.

We use a sample of the 13 most luminous WMAP Galactic free–free sources, responsible for 33% of the free–free emission of the Milky Way, to investigate star formation. The sample contains 40 star-forming complexes; we combine this sample with giant molecular cloud (GMC) catalogs in the literature to identify the host GMCs of 32 of the complexes. We estimate the star formation efficiency ϵGMC and star formation rate per free-fall time ϵff. We find that ϵGMC ranges from 0.002 to 0.2, with an ionizing luminosity-weighted average 〈ϵGMC〉Q = 0.08, compared to the Galactic average ≈0.005. Turning to the star formation rate per free-fall time, we find values that range up to . Weighting by ionizing luminosity, we find an average of 〈ϵff〉Q = 0.14–0.24 depending on the estimate of the age of the system. Once again, this is much larger than the Galaxy-wide average value ϵff = 0.006. We show that the lifetimes of GMCs at the mean mass found in our sample is 27 ± 12 Myr, a bit less than three free-fall times. The GMCs hosting the most luminous clusters are being disrupted by those clusters. Accordingly, we interpret the range in ϵff as the result of a time-variable star formation rate; the rate of star formation increases with the age of the host molecular cloud, until the stars disrupt the cloud. These results are inconsistent with the notion that the star formation rate in Milky Way GMCs is determined by the properties of supersonic turbulence.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a1b04604a04c56912b04a25c4a9e39f2e7fcf70b

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Citations in the corpus

The exciting lives of giant molecular clouds (2013, background): “1% to 20% (Evans et al. 2009; Murray 2011).”
A unified model for galactic discs: star formation, turbulence driving, and mass transport (2017, background): “…that the star formation rate is set by considerations of force and energy balance within a galactic disc (e.g. Thompson, Quataert & Murray 2005; Ostriker, McKee & Leroy 2010; Hopkins, Quataert & Murray 2011; Ostriker & Shetty 2011; Faucher-Giguère, Quataert & Hopkins 2013; Hayward & Hopkins 2017).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…environments), and generate galactic chimneys and super-bubbles c© 0000 RAS, MNRAS 000, 000–000 that generate fountains and super-winds (e.g. Krumholz et al. 2007, 2011; Offner et al. 2009, 2011; Harper-Clark & Murray 2011; Bate 2012; Wise et al. 2012; Pawlik et al. 2013; Muratov et al. 2013).”
TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, background): “In the Milky Way, the majority of star formation is concentrated in a few hundred massive GMCs (Mcl ∼ 106 M ), containing the majority of the Galaxy’s molecular gas reservoir (Murray 2011).”
Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “…on the fraction of GMCs that are spatially coincident with H II regions and young star clusters in nearby galaxies favor lifetimes of a few tens of Myrs (Engargiola et al. 2003; Blitz et al. 2007; Kawamura et al. 2009; Miura et al. 2012; see also Murray 2011; Meidt et al. 2015; Lee et al. 2016).”
SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES (2012, background): “In this sense, the evolution at high redshift could be regarded as more analogous to the lifecycle of individual GMCs (Murray 2011 and references therein).”
How Stellar Feedback Simultaneously Regulates Star Formation and Drives Outflows (2015, background): “In contrast,the actual efficiency is only a few per cent (e.g.Bigiel et al. 2008, 2011; Krumholz et al. 2012; Leroy et al. 2013), although the efficiency per free-fall time can be as high as unity for individual giant molecular clouds (GMCs;Murray 2011).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “For low-mass stars, outflows provide the primary feedback (e.g., Li & Nakamura 2006) while high-mass stars add radiation pressure and expanding H II regions (e.g., Murray 2011).”
The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, methodology): “…have been measured by classifying the clouds based on their star formation activity (Engargiola et al. 2003; Blitz et al. 2007; Kawamura et al. 2009; Murray 2011; Miura et al. 2012; Corbelli et al. 2017), or by quantifying the fraction of CO-bright versus Hα-bright lines of sight across each…”
(Star)bursts of FIRE: observational signatures of bursty star formation in galaxies (2015, background): “These clump masses are larger than for those of GMCs in the Milky Way, which usually form stellar masses of up to a few times 105 M (Murray 2011).”
Feedback-regulated star formation in molecular clouds and galactic discs (2013, background): “Regardless of the precise interpretation, the observations described by Murray (2011) demonstrate that GMCs hosting ∼ 1/3 of the current star formation rate in the Milky Way have GMCff well in excess of the galaxy-averaged value. disruption of GMCs by stellar feedback, showing that radiation…”
On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk (2014, background): “3 in Bolatto et al. 2008 and Table 1 in Murray 2011) and to the typical size of giant star complexes Article number, page 7 of 34 and superassociations (Elmegreen & Elmegreen 1983; Efremov 1995).”
ON THE INTERPLAY BETWEEN STAR FORMATION AND FEEDBACK IN GALAXY FORMATION SIMULATIONS (2014, background): “However, the values of ff estimated in this way are significantly lower than estimates for individual star forming regions, which have typical values in the range of ff,GMC ∼ 0.01 − 0.1 (Lada et al. 2010; Murray 2011; Evans et al. 2014).”
ANALYTICAL STAR FORMATION RATE FROM GRAVOTURBULENT FRAGMENTATION (2011, background): “The observed SFR per cloud free-fall time lies in the range 0.03 ∼SFRff ∼ 0.3, with a mean value 〈SFRff〉 ≈ 0.16 (Murray 2011, although see Feldmann & Gnedin 2011 for caution).”
Galaxies on FIRE (Feedback In Realistic Environments): stellar feedback explains cosmologically inefficient star formation (2013, background): “…under these conditions, HII heating should dominate), and this is completely consistent with both observations of star-forming regions (e.g. Lopez et al. 2011) and numerical radiation-hydrodynamic simulations of low-density, low-velocity clouds (Harper-Clark & Murray 2011; Sales et al. 2013).”
Before the first supernova: combined effects of H II regions and winds on molecular clouds (2014, unknown): “Coloured circles represent the simulation results and grey circles are taken from Table 2 in Murray (2011), who investigated 32 GMCs hosting the most luminous star–forming regions in the Milky Way.”
Variations in the Galactic star formation rate and density thresholds for star formation (2012, background): “(7) The reason this timescale is small compared to the average lifetime of stars in a cluster is because〈tQ〉 is dominated by stars>40 M⊙ (Murray 2011).”
Dark matter cores all the way down (2015, methodology): “In our fiducial models, we adopt a star formation efficiency per free fall time ff = 0.1 motivated by observations of local GMCs (Lada et al. 2010; Murray 2011; Evans et al. 2014), as well as recent numerical work (Hopkins et al. 2014; Agertz & Kravtsov 2015a) demonstrating how the interplay…”