The role of gas dynamical friction in the evolution of embedded stellar clusters

TL;DR

This paper investigates how gas dynamical friction influences the formation, density, and mass segregation of embedded stellar clusters, providing analytical criteria for cluster boundness and internal segregation based on clump properties.

Contribution

It offers new analytical insights into the role of gas dynamical friction in cluster formation and mass segregation, linking physical conditions to observed cluster properties.

Findings

Clusters in dense gas clumps can become bound after gas loss.

Massive subcondensations experience significant mass segregation.

Density thresholds determine cluster boundness and internal segregation levels.

Abstract

Two puzzles associated with open clusters have attracted a lot of attention -- their formation, with densities and velocity dispersions that are not too different from those of the star forming regions in the Galaxy, given that the observed Star Formation Efficiencies (SFE) are low and, the mass segregation observed / inferred in some of them, at ages significantly less than the dynamical relaxation times in them. Gas dynamical friction has been considered before as a mechanism for contracting embedded stellar clusters, by dissipating their energy. This would locally raise the SFE which might then allow bound clusters to form. Noticing that dynamical friction is inherently capable of producing mass segregation, since here, the dissipation rate is proportional to the mass of the body experiencing the force, we explore further, some of the details and implications of such a scenario, vis-a-vis observations. Making analytical approximations, we obtain a boundary value for the density of a star forming clump of given mass, such that, stellar clusters born in clumps which have densities higher than this, could emerge bound after gas loss, and for a clump of given mass and density, we find a critical mass such that, subcondensations with larger masses than this could suffer significant segregation within the clump.