Equilibrium Star Cluster Formation

By Jonathan C. Tan, Mark R. Krumholz, C. McKee. 2006

185 citations recorded by the source corpus.

We argue that rich star clusters take at least several local dynamical times to form and so are quasi-equilibrium structures during their assembly. Observations supporting this conclusion include morphologies of star-forming clumps, momentum flux of protostellar outflows from forming clusters, age spreads of stars in the Orion Nebula cluster (ONC) and other clusters, and the age of a dynamical ejection event from the ONC. We show that these long formation timescales are consistent with the expected star formation rate in turbulent gas, as recently evaluated by Krumholz & McKee. Finally, we discuss the implications of these timescales for star formation efficiencies, the disruption of gas by stellar feedback, mass segregation of stars, and the longevity of turbulence in molecular clumps.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/631ed033dfc6c6cd4ab77f4bbefb8b08dfc051a2

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Citations in the corpus

THE LONG-TERM EVOLUTION OF THE GALACTIC DISK TRACED BY DISSOLVING STAR CLUSTERS (2010, methodology): “To do so, we use a convenient form that expresses it in terms of a cloud’s mass M and column density Σ (Tan et al. 2006) tcr = 0.95√ αvirG ( M Σ3 )1/4 , (2) where αvir is the cloud’s virial ratio (Bertoldi & McKee 1992), essentially its ratio of kinetic to gravitational potential energy up to…”
The relation between the most-massive star and its parental star cluster mass (2009, background): “The formation of massive stars (> 10 M⊙) is still not well understood with at least two competing theories (competitive accretion vs. single star accretion) having been developed (Bonnell et al. 1998, 2004; Bonnell & Bate 2006; Tan et al. 2006; Krumholz et al. 2009).”
Molecular Clouds in the Milky Way (2015, background): “This evolutionary sequence is supported by the slow assembly time for stellar clusters within molecular clouds that is inferred from the age spread of cluster members and the absence of significant substructure (Tan et al. 2006). www.annualreviews.org • Galactic Molecular Clouds 619 A nn u.”
WHAT DRIVES THE EXPANSION OF GIANT H ii REGIONS?: A STUDY OF STELLAR FEEDBACK IN 30 DORADUS (2010, background): “Observational estimates range from a single free-fall time (Elmegreen 2000; Hartmann et al. 2001; Ballesteros-Paredes & Hartmann 2007) to several free-fall times (Tan et al. 2006).”
PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK (2016, background): “Others are in favor of star formation that would last for 4 − 10τdyn, where stellar feedback would maintain turbulence (Tan et al. 2006).”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, unknown): “…agreement with simulations, with the observed star formation rate in the Milky Way (Luna et al. 2006), with the age spreads of rich star clusters (Tan et al. 2006), with the star formation rate in dense molecular clumps (Krumholz & Tan 2006), and with the the Kennicutt-Schmidt Law for star…”
A Spitzer Census of the IC 348 Nebula (2007, background): “The relatively simple radial profile we find for central cluster members and the lack of substructure outside of the molecular cloud are consistent with the conclusion that the IC 348 cluster is at least one crossing time old (Tan et al. 2006).”
KINEMATIC AND SPATIAL SUBSTRUCTURE IN NGC 2264 (2015, background): “…formation theories are generally comprised of two classes: highly dynamic, non-equilibrium models that form within a crossing time (e.g., Bonnell et al. 2003; Bate 2012) and quasiequilibrium and/or slow contraction scenarios that require several crossing times to form (e.g., Tan et al. 2006).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “The self-regulating character of star formation has been studied profusely by the group around Christopher McKee (e.g. Tan et al. 2006) and has been shown to lead to decreasing star-formation efficiencies with increasing metallicity (Dib et al. 2010; Dib 2011; Dib et al. 2011).”
IONIZING PHOTON ESCAPE FRACTIONS FROM HIGH-REDSHIFT DWARF GALAXIES (2008, background): “We justify our choice of a threshold tdyn with inferred dynamical times from observations of star forming regions are approximately 700 kyr, and star formation occurs for several dynamical times (e.g. Tan et al. 2006).”
STELLAR FEEDBACK IN MOLECULAR CLOUDS AND ITS INFLUENCE ON THE MASS FUNCTION OF YOUNG STAR CLUSTERS (2009, background): “We assume that the timescale for ISM removal is a few crossing times: ∆t ∼ (1−10)×τc (Elmegreen 2000, 2007; Hartmann et al. 2001; Tan et al. 2006; Krumholz & Tan 2007).”
THE BIRTH OF A GALAXY: PRIMORDIAL METAL ENRICHMENT AND STELLAR POPULATIONS (2010, background): “Observations of star-forming regions show that the dynamical time is approximately 700 kyr and that SF is extended over several dynamical times (e.g. Tan et al. 2006), which motivates our choice of tdyn of our definition of molecular clouds in our SF prescription.”
The effect of magnetic fields on star cluster formation (2008, background): “One of the key areas of uncertainty is whether or not star formation is a rapid (Mac Low & Klessen 2004; Hartmann et al. 2001; Elmegreen 2007) or slow (Shu et al. 1987; Tan et al. 2006) process, central to which is the relative importance of magnetic fields to the star formation process.”
How do massive black holes get their gas (2009, background): “…and on small scales in galaxies (Kennicutt 1998; Kennicutt et al. 2007; Bigiel et al. 2008) and star formation efficiencies per dynamical time do not appear to evolve even in very dense regions (comparable to the highest gas densities modelled here; see, e.g. Tan et al. 2006; Krumholz & Tan 2007).”