2025A&A...699A.136R

Context. Star-forming regions are garnering considerable interest among the high-energy astrophysics community thanks to their potential as possible Galactic particle accelerators. In general, the role of electrons has not been fully considered in this kind of cosmic-ray source. However, the intense radiation fields inside these regions could make electrons significant gamma-ray contributors.
Aims. Our intention is to test whether its gamma-ray emission can be produced by cosmic-ray electrons by studying the young and compact star-forming region NGC 3603, a well known gamma-ray emitter.
Methods. We built a novel model by creating realistic 3D distributions of the gas and the radiation field in the region. We introduced these models into the PICARD code to perform cosmic-ray transport simulations and produce gamma-ray emission maps. We compared the results compared with a dedicated Fermi Large Area Telescope data analysis at high energies. We also explored the radio and neutrino emissions of the system.
Results. We improved the existing upper limits of the NGC 3603 gamma-ray source extension. Although the gamma-ray spectrum is aptly reproduced with the injection of CR protons, it requires a nearly 30% acceleration efficiency. In addition, the resulting extension of the simulated hadronic source is in mild tension with the extension data upper limit. The radio data disfavour the lepton-only scenario. Finally, after combining both populations, we find results that are consistent with all the observables, although the exact contributions remain ambiguous.