Speaker
Description
Massive stars strongly reshape their surroundings through radiation, stellar winds, and eventually supernova explosions, but when these different feedback mechanisms begin to dominate remains uncertain. We present VLA 3 GHz radio continuum observations of 13 nearby PHANGS galaxies to trace the evolution of star-forming regions during their first ~10 Myr. Combining these data with HST, JWST, VLT/MUSE, and AstroSat observations, we separate the radio emission into thermal free–free and non-thermal synchrotron components and connect their evolution to stellar age and other tracers of recent star formation. The radio observations also reveal a small population of 36 embedded, PAH- and dust-continuum-bright but optically faint star-forming regions, representing less than 10% of the radio sources and demonstrating the ability of radio emission to probe the earliest obscured phases of star formation. We find a clear evolution in radio properties with stellar age: from 1–3 to 6–10 Myr, the median thermal fraction decreases from ~61% to ~33%, while the median radio spectral index steepens from −0.05 to −0.51. The youngest regions already exhibit a non-thermal fraction of ~28% before the expected onset of core-collapse supernovae, suggesting that massive-star winds and associated shocks may contribute to early cosmic-ray acceleration. These results provide a resolved view of how radio emission evolves from the embedded phase through the emergence of synchrotron emission during the first ~10 Myr of stellar feedback.
