Why are most molecular clouds not gravitationally bound

By C. Dobbs, A. Burkert, J. W. M. Garching, Usm Munich, I. Cambridge. 2011

147 citations recorded by the source corpus.

The most recent observational evidence seems to indicate that giant molecular clouds are predominantly gravitationally unbound objects. In this paper we show that this is a natural consequence of a scenario in which cloud-cloud collisions and stellar feedback regulate the internal velocity dispersion of the gas, and so prevent global gravitational forces from becoming dominant. Thus, whilst the molecular gas is for the most part gravitationally unbound, local regions within the denser parts of the gas (within the clouds) do become bound and are able to form stars. We find that the observations, in terms of distributions of virial parameters and cloud structures, can be well modelled provided that the star formation efficiency in these bound regions is of the order of 5-10 per cent. We also find that in this picture the constituent gas of individual molecular clouds changes over relatively short time-scales, typically a few Myr.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/b578d0badf861fb3d4b891c848cfe2d7e669b969

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Citations in the corpus

The exciting lives of giant molecular clouds (2013, methodology): “In the vertical plane, Cloud 380 appears as one coherent structure, centred close to the midplane of the galaxy (see also Dobbs et al. 2011a for examples of edge on plots of simulated galaxies).”
Galaxies on FIRE (Feedback In Realistic Environments): stellar feedback explains cosmologically inefficient star formation (2013, background): “…strong stellar feedback, however, gas inside galaxies cools efficiently and collapses on a dynamical time, predicting order-unity star formation efficiencies on all scales (Hopkins et al. 2011; Tasker 2011; Bournaud et al. 2010; Dobbs et al. 2011; Krumholz et al. 2011; Harper-Clark & Murray 2011).”
Massive stars in massive clusters II: Disruption of bound clusters by photoionization (2012, background): “…ratio of the clouds in the Heyer et al. (2009) sample is not independent of cloud mass, but instead declines with increasing mass, so that more massive clouds are more likely to be bound, and in fact very few clouds with masses in excess of 104M⊙ were found to be unbound by Dobbs et al. (2011).”
The meaning and consequences of star formation criteria in galaxy models with resolved stellar feedback (2013, unknown): “17-18 & Dobbs et al. 2011.”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “A second picture, exemplified by Dobbs et al. (2011), is that most clouds and most parts of clouds are not gravitationally bound but are transient objects.”
TOWARD A COMPLETE ACCOUNTING OF ENERGY AND MOMENTUM FROM STELLAR FEEDBACK IN GALAXY FORMATION SIMULATIONS (2012, background): “This can be partly due to the fact that natal GMCs are not gravitationally bound (Mac Low & Klessen 2004; Padoan et al. 1997; Li et al. 2004; Kritsuk et al. 2007; Dobbs et al. 2011).”
The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, background): “…favour theories suggesting that molecular clouds are short-lived, transient objects that form, evolve, and disperse on a (cloud-scale or galactic) dynamical time (e.g. Elmegreen 2000; Dobbs et al. 2011; Grudić et al. 2018; Jeffreson & Kruijssen 2018; Semenov MNRAS 000, 1–37 (2019) et al. 2018).”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, background): “Dobbs et al. (2011) suggest that clouds in their entirety are unbound on large spatial scales& 10 pc.”
EVOLVING GRAVITATIONALLY UNSTABLE DISKS OVER COSMIC TIME: IMPLICATIONS FOR THICK DISK FORMATION (2011, background): “Simulations of isolated galaxies (Bournaud et al. 2011; Dobbs et al. 2011a,b) with initial conditions set such that Q < 1 provide a higher resolution view of such galaxies over a few outer orbits of the disk.”
On the fraction of star formation occurring in bound stellar clusters (2012, background): “A fiducial value of αvir = 1.3 (McKee & Tan 2003) is adopted here, but it should be noted that values in the range αvir = 0.2–10 are found in observations (Solomon et al. 1987; Heyer et al. 2009) and numerical work (Tasker & Tan 2009; Dobbs et al. 2011b; Hopkins, Quataert & Murray 2012).”
Rotational support of giant clumps in high-z disc galaxies (2011, background): “…1 (Bournaud et al. 2007; Ceverino et al. 2010; Genzel et al. 2011), the self-gravitating collapse of the low-z GMCs could be triggered by the formation of non-linear perturbations due to gas compression associated with spiral density waves (see also Dobbs et al. 2011) or supersonic turbulent flows.”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…of stellar feedback, most gas accreted into galaxies should cool rapidly on a timescale much shorter than the dynamical time, collapse, fragment, and turn into stars (Bournaud et al. 2010; Tasker 2011; Hopkins et al. 2011; Dobbs et al. 2011; Krumholz et al. 2011; Harper-Clark & Murray 2011).”
The structure of the interstellar medium of star‐forming galaxies (2011, background): “This is why (as we saw with other cloud properties) models with very different assumptions and more simplified models for feedback have also seen similar characteristic α (Dobbs et al. 2011).”
Implementing molecular hydrogen in hydrodynamic simulations of galaxy formation (2012, background): “Dobbs (2008); Dobbs et al. (2011) and Tasker (2011) studied th formation, orbits, and mass distributions of MCs in models of piral galaxies by identifying gas clumps where MCs would be.”