# The Evolution and Properties of Rotating Massive Star Populations

## TL;DR

This study models the evolution of rotating massive stars and their impact on ionizing radiation, revealing the importance of fast rotators in sustaining ionizing photon production in young stellar populations, with implications for cosmic reionization.

## Contribution

It introduces new stellar population synthesis models incorporating rotation effects and very massive stars, extending previous models to better match observations and high-redshift galaxy data.

## Key findings

- Fast-rotating stars significantly influence ionizing photon output.
- Models align with observations of young nuclear star clusters.
- Rotation effects are crucial for understanding high-redshift galaxy emission lines.

## Abstract

We investigate the integrated properties of massive (>10 Msun), rotating, single-star stellar populations for a variety of initial rotation rates (v/vcrit=0.0, 0.2, 0.4, 0.5, and 0.6). We couple the new MESA Isochrone and Stellar Tracks (MIST) models to the Flexible Stellar Population Synthesis (FSPS) package, extending the stellar population synthesis models to include the contributions from very massive stars (>100 Msun), which can be significant in the first ~4 Myr after a starburst. These models predict ionizing luminosities that are consistent with recent observations of young nuclear star clusters. We also construct composite stellar populations assuming a distribution of initial rotation rates. Even in low-metallicity environments where rotation has a significant effect on the evolution of massive stars, we find that stellar population models require a significant contribution from fast-rotating (v/vcrit>0.4) stars in order to sustain the production of ionizing photons beyond a few Myr following a starburst. These results have potentially important implications for cosmic reionization by massive stars and the interpretation of nebular emission lines in high-redshift star-forming galaxies.