Stellar feedback effects on the mass distribution of clouds and cloud complexes

Context. Galaxy evolution is sensitive to how stars inject feedback into their surroundings. In particular, the stellar feedback from star clusters strongly affects gas motions and, consequently, the baryonic cycle. More massive clusters have stronger effects. Our previous results show that the star cluster mass distribution in dwarf galaxies depends on feedback because strong pre-supernova feedback, particularly ionizing radiation, results in fewer high-mass star clusters. Aims. We investigated the mass distribution of gas clouds in dwarf galaxies. Since star clusters form from the collapse of gas clouds, we expected similar feedback dependences in both their mass distributions; we thus hypothesized that pre-supernova feedback results in fewer high-mass gas clouds. Methods. To test our hypothesis, we used an isocontour analysis at three cutoff densities n = 10, 101.5, and 102 cm−3 to identify gas clouds from dwarf galaxy simulations performed with the RAMSES adaptive mesh refinement code. We calculated mass distributions for models that implement different combinations of the feedback modes: supernovae, stellar winds from massive stars, and ionizing radiation. Results. We find that the mass distribution for clouds with n > 100 cm−3 is independent of feedback, but that the mass distribution for cloud complexes with n > 10 cm−3 is more top-heavy in the presence of radiation. Winds do not affect the mass distribution at any of the scales we studied. Conclusions. This contradicts our hypothesis that the mass distribution of gas clouds would show a similar feedback dependence as the mass distribution of star clusters. Instead, our results show no feedback dependence in the mass function of dense clouds with n > 100 cm−3, suggesting their mass distribution is predominantly set by gravity. We conclude that the shape of the star cluster mass function must be determined by a combination of intra-cloud feedback regulation of star formation (i.e., regulation of star formation within a cloud due to the feedback of stars formed from that cloud itself) and, in the case of radiation, effects on the temperature of the parent gas clouds.