On the X‐Ray Emission from Massive Star Clusters and Their Evolving Superbubbles

The X-ray emission properties from the hot thermalized plasma that resultsfrom the collisions of individual stellar winds and supernovae ejecta withinrich and compact star clusters are discussed. We propose a simple analyticalway of estimating the X-ray emission generated by super star clusters andderive an expression that indicates how this X-ray emission depends on the maincluster parameters. Our model predicts that the X-ray luminosity from the starcluster region is highly dependent on the star cluster wind terminal speed, aquantity related to the temperature of the thermalized ejecta.We have alsocompared the X-ray luminosity from the SSC plasma with the luminosity of theinterstellar bubbles generated from the mechanical interaction of the highvelocity star cluster winds with the ISM.We found that the hard (2.0 keV - 8.0keV) X-ray emission is usually dominated by the hotter SSC plasma whereas thesoft (0.3 keV - 2.0 keV) component is dominated by the bubble plasma. Thisimplies that compact and massive star clusters should be detected as point-likehard X-ray sources embedded into extended regions of soft diffuse X-rayemission. We also compared our results with predictions from the populationsynthesis models that take into consideration binary systems and found that inthe case of young,massive and compact super star clusters the X-ray emissionfrom the thermalized star cluster plasma may be comparable or even larger thanthat expected from the HMXB population.Comment: 24 pages, 8 figures, Accepted for publication in The Astrophysical Journa