Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

Abstract

The self-enrichment of massive star clusters by p-processed elements is shown to increase significantly with increasing gas density as a result of enhanced star formation rates and stellar scatterings compared to the lifetime of a massive star. Considering the type of cloud core where a globular cluster might have formed, we follow the evolution and enrichment of the gas and the time dependence of stellar mass. A key assumption is that interactions between massive stars are important at high density, including interactions between massive stars and massive star binaries that can shred stellar envelopes. Massive-star interactions should also scatter low-mass stars out of the cluster. Reasonable agreement with the observations is obtained for a cloud core mass of ∼ 4 × 10 6 M ⊙ and a density of ∼ 2 × 10 6 cm −3 . The results depend primarily on a few dimensionless parameters, including, most importantly, the ratio of the gas consumption time to the lifetime of a massive star, which has to be low, ∼ 10%, and the efficiency of scattering low-mass stars per unit dynamical time, which has to be relatively large, such as a few percent. Also for these conditions, the velocity dispersions of embedded globular clusters should be comparable to the high gas dispersions of galaxies at that time, so that stellar ejection by multi-star interactions could cause low-mass stars to leave a dwarf galaxy host altogether. This could solve the problem of missing first-generation stars in the halos of Fornax and WLM.

Simulating the spatial distribution and kinematics of globular clusters within galaxy clusters in illustris

“…Some of the observed trends in GCs can be explained in models where they trace the most turbulent, high density and gas rich star formation episodes in galaxies (Gnedin et al 2004;Prieto & Gnedin 2008), and analytical calculations support such view (Kruijssen & Cooper 2012;Kruijssen 2015;Elmegreen 2017). Other scenarios where GCs are placed at the centers of their own dark matter halo (Peebles 1984;Rosenblatt et al 1988) and form completely independent of their host galaxy are, although compelling, currently disfavoured due to the large degree of tidal stripping expected and the observationally constrained abundances and radial distribution of GCs around galaxies (Carlberg 2018;Creasey et al 2019).…”

On the early evolution of massive star clusters: the case of cloud D1 and its embedded cluster in NGC 5253

“…As in molecular clouds the gas pressure is dominated by turbulence (e.g. Elmegreen & Efremov 1997;Elmegreen 2017;Johnson et al 2015), equation (9) also allows one to obtain the gas one-dimensional velocity dispersion σ 2 (r) = Pg(r)/ρg(r) (Smith & Gallagher 2001). The distribution of the gas density, pressure and velocity dispersion in a Gaussian star-forming cloud with a total mass Mtot = 4.64 × 10 5 M⊙ global star formation efficiency ǫ = 0.35 and the gas and stellar mass distribution core radii a = 2.4pc and b = 0.8pc, is shown in Fig.…”

Explaining the Multiple Populations in Globular Clusters by Multiple Episodes of Star Formation and Enrichment without Gas Expulsion from Massive Star Feedback

“…For all stellar generations, we assume a fixed SFE and a single-slope IMF, φ(m), with masses ranging from 0.1 2 A successive enrichment process has also been suggested by Elmegreen (2017) in his investigation based on interacting massive stars and MIB. The timescale for the formation of multiple populations in his models, however, is two orders of magnitude smaller than those predicted in our models because SNe explosions are assumed to clear out the remaining gas preventing further star formation.…”