Star cluster disruption by giant molecular clouds

By M. Gieles, S. P. Portegies Zwart, H. Baumgardt, E. Athanassoula, H. Lamers, Michael Sipior, J. University, U. Amsterdam, Argelander Institute for Astronomy Bonn Observatoire de Marseille. 2006

204 citations recorded by the source corpus.

We investigate encounters between giant molecular clouds (GMCs) and star clusters. We propose a single expression for the energy gain of a cluster due to an encounter with a GMC, valid for all encounter distances and GMC properties. This relation is verified with N-body simulations of cluster-GMC encounters, where the GMC is represented by a moving analytical potential. Excellent agreement is found between the simulations and the analytical work for fractional energy gains of Delta E/vertical bar E-0 vertical bar < 10, where vertical bar E-0 vertical bar is the initial total cluster energy. The fractional mass loss from the cluster scales with the fractional energy gain as (Delta M/M-0) = f(Delta E/vertical bar E-0 vertical bar), where f similar or equal to 0.25. This is because a fraction 1 - f of the injected energy goes to the velocities of escaping stars, that are higher than the escape velocity. We therefore suggest that the disruption time of clusters, t(dis), is best defined as the time needed to bring the cluster mass to zero, instead of the time needed to inject the initial cluster energy. We derive an expression for t(dis) based on the mass loss from the simulations, taking into account the effect of gravitational focusing by the GMC. Assuming spatially homogeneous distributions of clusters and GMCs with a relative velocity dispersion of sigma(cn), we find that clusters lose most of their mass in relatively close encounters with high relative velocities (similar to 2 sigma(cn)). The disruption time depends on the cluster mass (M-c) and half-mass radius (r(h)) as t(dis) = 2.0 S(M-c/10(4) M-circle dot)(3.75 pc/r(h))(3) Gyr, with S equivalent to 1 for the solar neighbourhood and S scales with the surface density of individual GMCs (Sigma(n)) and the global GMC density (rho(n)) as S proportional to (Sigma(n)rho(n))(-1). Combined with the observed relation between r(h) and M-c, that is, r(h) proportional to M-c(lambda), t(dis) depends on M-c as t(dis)proportional to M-c(gamma). The index gamma is then defined as gamma= 1 - 3 lambda. The observed shallow relation between cluster radius and mass (e.g. lambda similar or equal to 0.1), makes the value of the index gamma = 0.7 similar to that found from observations and from simulations of clusters dissolving in tidal fields (gamma similar or equal to 0.62). The constant of 2.0 Gyr, which is the disruption time of a 10(4) M circle dot cluster in the solar neighbourhood, is about a factor of 3.5 shorter than that found from earlier simulations of clusters dissolving under the combined effect of Galactic tidal field and stellar evolution. It is somewhat higher than the observationally determined value of 1.3 Gyr. It suggests, however, that the combined effect of tidal field and encounters with GMCs can explain the lack of old open clusters in the solar neighbourhood. GMC encounters can also explain the (very) short disruption time that was observed for star clusters in the central region of M51, since there rho(n) is an order of magnitude higher than that in the solar neighbourhood.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/19a0470de35bb42de92c368d36c7f2320585ade5

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Citations in the corpus

Young Massive Star Clusters (2010, background): “Variations in dissolution time scales are explained by differences in the tidal field strength (Lamers, Gieles & Portegies Zwart 2005) and the GMC density (Gieles et al. 2006c).”
What controls star formation in the central 500 pc of the Galaxy (2013, unknown): “The time-scale for disruption is thentshdis ∝ Σ−1GMCρ−1molρYMC (Gieles et al. 2006), withΣGMC the GMC surface density,ρmol the spatially averaged molecular gas density, andρYMC the YMC density.”
Globular cluster systems in nearby dwarf galaxies – III. Formation efficiencies of old globular clusters (2010, background): “…which shapes the initial power-law to the observed, present-day Gaussian globular cluster luminosity function (GCLF, see e.g. Fall & Zhang 2001; Goudfrooij et al. 2004, 2007; Gieles et al. 2006; McLaughlin & Fall 2008; Kruijssen & Portegies Zwart 2009; Elmegreen 2010, and references therein).”
A general catalogue of extended objects in the Magellanic System (2008, background): “Such processes lead to the disruption of most star clusters in a mass-dependent time-scale shorter than ≈ 1Gyr (Gieles et al. 2006).”
A Gaia DR2 view of the open cluster population in the Milky Way (2018, background): “…will be disrupted in their first few million years of existence, due Article published by EDP Sciences A93, page 1 of 16 to mechanisms possibly involving gas loss driven by stellar feedback (Moeckel & Bate 2010; Brinkmann et al. 2017) or encounters with giant molecular clouds (Gieles et al. 2006).”
Gas expulsion and the destruction of massive young clusters (2006, unknown): “In some cases, even older clusters may become perturbed (by tidal or impulsive interactions, e.g. Gieles et al. 2006) pushing them out of equilibrium causing them to move away from the canonical DMtL line, however we would expect this to be fairly rare.”
The dynamical state of stellar structure in star‐forming regions (2011, background): “Although the disruption rate due to tidal shocks decreases with cluster density, sufficiently strong12 shocks would still be able to disrupt dense clusters13 (Gieles et al. 2006).”
Merging black holes in young star clusters (2019, background): “The choice of terminating the simulations at t = 100 Myr is motivated by the fact that our tidal field model tends to overestimate the lifetime of SCs, because we do not account for massive perturbers (e.g. molecular clouds), which accelerate the SC disruption (Gieles et al. 2006).”
Globular clusters as the relics of regular star formation in ‘normal’ high-redshift galaxies (2015, background): “…high-mass end, the ICMF has a truncation that is well-fit by an exponential function [dN/dMi ∝ Mαi exp (−Mi/Mc), where Mc is the truncation mass, see e.g.Gieles et al. 2006a; Larsen 2009; Bastian et al. 2012], which was originally proposed bySchechter (1976) to describe the galaxy mass function.”
On the star formation rate – brightest cluster relation: estimating the peak star formation rate in post-merger galaxies (2008, methodology): “Gieles et al. (2006a) have suggested that instead of a power-law mass function, the underlying mass distribution of clusters is better described by a Schechter function.”
On the fraction of star formation occurring in bound stellar clusters (2012, methodology): “…should be addressed by building on more detailed numerical modelling, both accounting for the internal cluster dynamics (e.g. Baumgardt & Makino 2003; Kruijssen 2009; Gieles, Heggie & Zhao 2011) and the disruptive influence of the galactic environment (Gieles et al. 2006b; Kruijssen et al. 2011).”