On the Heating Efficiency Derived from Observations of Young Super Star Clusters in M82

TL;DR

This study analyzes the heating efficiency of young super star clusters in M82, revealing that most of their mechanical energy is lost internally, resulting in low energy output and limited impact on the galaxy's interstellar medium.

Contribution

It applies an analytic model to measure heating efficiency in multiple clusters, showing most have efficiencies below 10%, which challenges previous assumptions about their feedback.

Findings

Heating efficiency does not exceed 10% in studied clusters.

Low efficiency leads to reduced mechanical energy transfer to the ISM.

Clusters evolve in a bimodal hydrodynamic regime with significant radiative cooling.

Abstract

Here we discuss the mechanical feedback that massive stellar clusters provide to the interstellar medium of their host galaxy. We apply an analytic theory developed in a previous study for M82-A1 to a sample of 10 clusters located in the central zone of the starburst galaxy M82, all surrounded by compact and dense HII regions. We claim that the only way that such HII regions can survive around the selected clusters, is if they are embedded into a high pressure ISM and if the majority of their mechanical energy is lost within the star cluster volume via strong radiative cooling. The latter implies that these clusters have a low heating efficiency, $\eta$, and evolve in the bimodal hydrodynamic regime. In this regime the shock-heated plasma in the central zones of a cluster becomes thermally unstable, loses its pressure and is accumulated there, whereas the matter injected by supernovae and stellar winds outside of this volume forms a high velocity outflow - the star cluster wind. We calculated the heating efficiency for each of the selected clusters and found that in all cases it does not exceed 10% . Such low heating efficiency values imply a low mechanical energy output and the impact that the selected clusters provide to the ISM of M82 is thus much smaller than what one would expect using stellar cluster synthetic models.