Speaker
Description
Star-forming environments such as star-forming and Starburst Galaxies (SFGs and SBGs) experience intense phases of stellar formation activity. The Fermi-LAT collaboration has found a correlation between the gamma-ray and infrared luminosities for a sample of local SFGs and SBGs. Yet, the nature of CR transport inside these sources is still under debate. In this talk, I will discuss novel and tight constraints between CR transport in these sources and the star formation rate (SFR), exploiting 15 years of public Fermi-LAT data. Firstly, I will demonstrate that there is an indication at ~$4\sigma$ level from other two starburst galaxies, M83 and NGC 1365, strengthening even more the correlation between gamma-rays and SFR. However, sources like NGC 6946 and IC 342 do not show any evidence of gamma-ray emission despite correlating with the most energetic CRs ever observed. Secondly, I will argue that local SFGs are consistent with CR escape dominated by advection rather than diffusion and that the degree of calorimetry increases with the SFR. Furthermore, unresolved sources strongly reduce the degree of calorimetry of SBGs, thereby decreasing the contribution of SBGs into the diffuse gamma-ray and neutrino backgrounds. This intrinsically implies that if star-forming activity were able to accelerate ultra-high energy CRs, their corresponding gamma-ray and neutrino emission might be dim. Finally, I will show that the SFG and SBG contribution cannot saturate the the isotropic gamma-ray background (IGRB) measured by Fermi-LAT while being consistent with a $\sim$20\% contribution to the 6-year Cascade diffuse neutrino flux measured by the IceCube Neutrino Observatory.
