On the fraction of star formation occurring in bound stellar clusters

By D. Kruijssen. 2012

315 citations recorded by the source corpus.

We present a theoretical framework in which bound stellar clusters arise naturally at the high-density end of the hierarchy of the interstellar medium (ISM). Due to short free-fall times, these high-density regions achieve high local star formation efficiencies, enabling them to form bound clusters. Star-forming regions of lower density remain substructured and gas-rich, ending up unbound when the residual gas is expelled. Additionally, the tidal perturbation of star-forming regions by nearby, dense giant molecular clouds imposes a minimum density contrast required for the collapse to a bound cluster. The fraction of all star formation that occurs in bound stellar clusters (the cluster formation efficiency, hereafter CFE) follows by integration of these local clustering and survival properties over the full density spectrum of the ISM, and hence is set by galaxy-scale physics. We derive the CFE as a function of observable galaxy properties, and find that it increases with the gas surface density, from Γ ∼ 1 per cent in low-density galaxies to a peak value of Γ ∼ 70 per cent at densities of Σg ∼ 103 M⊙ pc−2. This explains the observation that the CFE increases with the star formation rate density in nearby dwarf, spiral and starburst galaxies. Indeed, comparing our model results with observed galaxies yields excellent agreement. The model is applied further by calculating the spatial variation of the CFE within single galaxies. We also consider the variation of the CFE with cosmic time and show that it increases with redshift, peaking in high-redshift, gas-rich disc galaxies. It is estimated that up to 30–35 per cent of all stars in the Universe once formed in bound stellar clusters. We discuss how our theory can be verified with Gaia and ALMA, and provide possible implementations for theoretical work and for simulations of galaxy formation and evolution.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/158fd6474aa992ff54c6af860a3a3f988ed31d8f

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Citations in the corpus

Kinematics in Young Star Clusters and Associations with Gaia DR2 (2018, background): “G A ] 1 1 N ov as well as changes in the gravitational potential due to the dispersal of the molecular cloud (e.g., Tutukov 1978; Hills 1980) and tidal interactions with clouds and clusters (e.g., Kruijssen 2012).”
A Catalog of Newly Identified Star Clusters in Gaia DR2 (2019, background): “Perturbed by disk shocks, spiral arm passages, and encounters with molecular clouds (Spitzer 1958; Kruijssen 2012), OCs expand and disrupt at a timescale of 200Myr–1 Gyr (Yang et al. 2013; Pang et al. 2018).”
Probing the role of the galactic environment in the formation of stellar clusters, using M83 as a test bench (2015, methodology): “…-10.27 0.59+0.19 −0.14 0.60±0.12 -2.35± 0.13 3.30–4.50 0.23±0.02 0.33±0.03 14.0±2.6 12.6±2.2 13.0 18.3 -10.55 0.39+0.04 −0.05 0.30±0.06 -2.50±0.13 a Properties of the galaxy and cluster population integrated within 0.45 and 4.5 kpc. b Value from Kruijssen (2012). stantially larger cluster sample.”
The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, methodology): “MNRAS 000, 1–22 (2018) star formation occurring in bound clusters (Bastian 2008; Goddard et al. 2010, the cluster formation efficiency) is environmentally dependent according to the model of Kruijssen (2012).”
What controls star formation in the central 500 pc of the Galaxy (2013, methodology): “Because the gas needs to reach high densities before becoming gravitationally unstable and forming stars, it is likely that much of the starformation in the entire CMZ occurs in bound stellar clusters (see§3.1.2 and Kruijssen 2012; Longmore et al. 2013b).”
CO-EVOLUTION OF GALACTIC NUCLEI AND GLOBULAR CLUSTER SYSTEMS (2013, background): “This is the simplest assumption; in detail, the cluster fraction may scale with the local gas density (e.g., Kruijssen 2012).”
Cloud-scale Molecular Gas Properties in 15 Nearby Galaxies (2018, background): “Specifically, most modern star formation theories predict a strong dependence of the star formation efficiency per free-fall time on the virial parameter and the turbulent pressure (Kruijssen 2012; Krumholz et al. 2012; Hennebelle & Chabrier 2013; Padoan et al. 2017, among many others).”
An uncertainty principle for star formation - I. Why galactic star formation relations break down below a certain spatial scale (2014, background): “5 with about 0.3–0.5 dex scatter (Krumholz & McKee 2005; Kruijssen 2012) because they simultaneously satisfy the ScmidtKennicutt and Silk-Elmegreen SF relations (Schmidt 1959; Silk 1997; Elmegreen 1997; Kennicutt 1998).”
The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline (2014, background): “About50% of the star formation in the CMZ is thought to occur in bound clusters as shown by observations (Mauerhan et al. 2010) and theory (Kruijssen 2012), ofwhich the majority is destroyed on time-scales of∼ 10 Myr (see e.g. Portegies Zwart et al. 2001; Kruijssen et al. 2011, 2014).”
Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies (2015, methodology): “These conditions give rise to high CFEs (Γ ∼ 0.5, Kruijssen 2012) and Toomre masses (MT >∼ 10 8 M⊙ and therefore MT,cl >∼ 10 6.5, Kruijssen 2014), both of which promote the formation of GC-like YMCs.”