Electron Kappa Distributions in Astrophysical Nebulae

Abstract

Until recently, it had been assumed that the electrons in astrophysical nebulae (HII regions and planetary nebulae) are in thermal equilibrium, with energies described by the Maxwell–Boltzmann distribution. This may not always be true. Based on satellite and space probe measurements of electron energies in the solar system, where nonequilibrium energy distributions are regularly encountered, it appears to be entirely plausible that such distributions also occur in nebulae, under similar physical conditions. If we adopt kappa distributions for the nebulae electron energies, we can resolve a long-standing problem where measurements of electron temperatures and chemical abundances using different methods yield discrepant results. This has been a major concern, as measurements of nebular abundances are widely used to study galaxy evolution and dynamics. By assuming nonequilibrium electron energies, we can resolve the measurement discrepancies and gain a deeper understanding of the physics in these regions. Show more