Feedback From Massive Stars and Gas Expulsion From Proto-Globular Clusters

Abstract

Globular clusters (GCs) are considerably more complex structures than previously thought, harboring at least two stellar generations that present clearly distinct chemical abundances. Scenarios explaining the abundance patterns in GCs mostly assume that originally the clusters had to be much more massive than today, and that the second generation of stars originates from the gas shed by stars of the first generation (FG). The lack of metallicity spread in most GCs further requires that the supernova-enriched gas ejected by the FG is completely lost within ∼30 Myr, a hypothesis never tested by means of three-dimensional hydrodynamic simulations. In this paper, we use 3D hydrodynamic simulations including stellar feedback from winds and supernovae, radiative cooling and self-gravity to study whether a realistic distribution of OB associations in a massive proto-GC of initial mass M tot ∼107 M e is sufficient to expel its entire gas content. Our numerical experiment shows that the coherence of different associations plays a fundamental role: as the bubbles interact, distort, and merge, they carve narrow tunnels that reach deeper and deeper toward the innermost cluster regions, and through which the gas is able to escape. Our results indicate that after 3 Myr, the feedback from stellar winds is responsible for the removal of ∼40% of the pristine gas, and that after 14 Myr, 99% of the initial gas mass has been removed.

Gas expulsion in massive star clusters?

“…Second, a steady, moderately massloaded wind (e.g., Palouš et al 2013;Calura et al 2015) may remove gas over timescales that are long compared to the crossing time, which is probably what occurs in galactic winds (e.g., Strickland & Heckman 2009;von Glasow et al 2013). In this case, the change in gravitational potential is comparatively slow, such that the effect on the stellar kinematics is moderate, and the fraction of stars lost is small (Baumgardt & Kroupa 2007).…”

“…This is again a factor that makes it easier for gas expulsion to occur in our simple models, where energy input effectively happens at the cluster centre. Calura et al (2015) simulate an embedded star cluster with compactness index C 5 = 0.85 and a metallicity of [Fe/H] = −1.3. For these parameters, our simple model predicts a minimum local star formation efficiency for gas expulsion on the crossing timescale of 0.61 in the wind phase, and, respectively 0.41 in the supernova phase.…”

Paving the way for the JWST: witnessing globular cluster formation at z > 3

“…These assumptions ensure a significant mass loss of FG stars due to the external potential. If the energy injected by the FG stellar winds and SNe is sufficient to expel the SN ejecta and the residual gas (Calura et al 2015), the stellar FG can expand beyond its tidal limit in response to this substantial gas loss and be prone to efficient stellar mass loss due to the external field (D'Ercole et al 2008). Clearly, the efficiency of this mechanism is sensitive to the parameters regulating the initial FG distribution, as more concentrated stellar distributions will give place to smaller amounts of mass lost via tidal stripping (e.g., Vesperini & Heggie 1997).…”

“…As recent hydrodynamical simulations of proto-GCs have shown (Calura et al 2015), the feedback of the stellar winds and SNe belonging to the FG can produce large and elongated hot cavities along which their interstellar gas is able to escape. In principle, these channels may also represent viable escape routes for ionizing photons.…”

Exponentially growing bubbles around early supermassive black holes

“…The simulation was performed using a customized version of the RAMSES code (Teyssier 2002) as described by Calura et al (2015). The initial conditions are represented by a uniform and homogeneous distribution of gas characterized by a density of 10 −28 g cm −3 and temperature 10 4 K (see Section 4.4).…”