Characterising emission line nebulae in nearby galaxies
The ionized interstellar medium (ISM) is a central part of the galactic ecosystem, where the interaction between stars and gas becomes exceptionally vivid. Its main constituents – H II regions, planetary nebulae (PNe), and supernova remnants (SNRs) – trace different phases of stellar evolution and provide complementary perspectives on feedback and galactic structure. The emergence of integral field spectroscopy (IFS) has opened new insights and enabled studies of the various components in unprecedented detail. We use a combination of observations – including MUSE spectroscopy and high-resolution HST imaging – across a diverse sample of nearby star-forming galaxies to study various aspects of emission line nebulae. In the first part of this thesis, we construct a dedicated PNe catalogue and measure the distance to each galaxy with the PNLF. The results highlight the potential of this method, but also its challenges, such as misclassified PNe or internal extinction. The second part links H II regions to the young stellar populations that power them. We identify potential age tracers – such as the equivalent width EW, the flux ratio H$\alpha$/FUV, and the ionization parameter $\log q$ – that all show a correlation with stellar age. Building on this catalogue, we compare the predicted ionizing photon flux from the stars to the observed flux from the \HII region to compute the escape fraction of ionizing photons. Individual regions yield comparatively high escape fractions, though with large variations and significant uncertainties. When combining all nebulae and stars on a galactic scale, the value remains high, but it becomes more robust and consistent across the galaxy sample. It makes it clear that stellar feedback is not locally bound, but influences the galaxies as a whole.
