Stellar associations powering H

Newly formed stars profoundly affect their environment by depositing energy and momentum into the surrounding gas. However, only a fraction of the stellar feedback is retained in the cloud, and observational constraints are needed to improve our understanding of this process. In a sample of 19 nearby galaxies, we matched H <ns0:sc>II</ns0:sc> regions from PHANGS–MUSE to their ionizing stellar source from PHANGS–HST and measured the percentage of ionizing radiation that leaks into the surrounding diffuse ionised gas (DIG). Based on a catalogue in which each H <ns0:sc>II</ns0:sc> region is powered by a single young and massive stellar association, we measure a photon escape fraction of fesc = 82−24+12 %. We obtain comparable results when using different procedures to match the ionised gas to its source. All samples in our study contain a substantial fraction of objects (up to 20%), in which the stellar source is insufficient to produce the H α flux observed from the nebula. Many of these cases are probably related to uncertain age estimates, but we also find numerous regions for which a significant fraction of the ionising photon budget is contributed by stars that reside outside the boundaries of the H <ns0:sc>II</ns0:sc> region. This finding motivates the use of an alternative galaxy-wide approach in which we include all H <ns0:sc>II</ns0:sc> regions and stellar sources, not just those that show a clear overlap. When we sum the ionisation budget over entire galaxies, we measure slightly lower, but consistent values.