Are hierarchically formed embedded star clusters surviving gas expulsion depending on their initial conditions?

TL;DR

This study uses N-body simulations to explore how initial conditions of embedded star clusters influence their survival after gas expulsion, revealing that realistic mass functions lead to lower bound mass fractions over time.

Contribution

It introduces a detailed simulation approach with realistic initial mass functions and compares results with analytical models, highlighting the impact of initial conditions on cluster survival.

Findings

Bound mass fraction can be predicted immediately after gas expulsion.

Realistic mass functions cause lower bound mass fractions at later stages.

Primordial mass segregation level does not significantly affect outcomes.

Abstract

We investigate the dissolution process of young embedded star clusters with different primordial mass segregation levels using fractal distributions by means of N-body simulations. We combine several star clusters in virial and subvirial global states with Plummer and uniform density profiles to mimic the gas. The star clusters have masses of Mstars = 500 Mo which follow an initial mass function where the stars have maximum distances from the centre of r = 1.5 pc. The clusters are placed in clouds which at the same radius have masses of Mcloud = 2000 Mo, resulting in star formation efficiency of 0.2. We remove the background potential instantaneously at a very early phase, mimicking the most destructive scenario of gas expulsion. The evolution of the fraction of bound stellar mass is followed for a total of 16 Myr for simulations with stellar evolution and without. We compare our results with previous works using equal-mass particles where an analytical physical model was used to estimate the bound mass fraction after gas expulsion. We find that independent of the initial condition, the fraction of bound stellar mass can be well predicted just right after the gas expulsion, but tends to be lower at later stages, as these systems evolve due to the stronger two-body interactions resulting from the inclusion of a realistic initial mass function. This discrepancy is independent of the primordial mass segregation level.