We discuss recent claims that the free electrons in ionized nebulae may not have a significantly Maxwellian velocity distribution. Supra-thermal electrons, electrons with much more energy than is encountered at electron temperatures found in nebulae, may solve the t2/ADF puzzle, the observations that abundances obtained from recombination and collisionally excited lines do not agree, and that different temperature indicators give different results. These non-Maxwellian electrons can be designated by the kappa formalism. We show that the distance over which heating rates change are much longer than the distance supra-thermal electrons can travel, and that the timescale to thermalize these electrons are much shorter than the heating or cooling timescales. These estimates show that supra-thermal electrons will have disappeared into the Maxwellian velocity distribution long before they affect the collisionally-excited forbidden and recombination lines, so the electron velocity distribution will be closely thermal.

Document Type


Publication Date


Notes/Citation Information

Published in Revista Mexicana de Astronomía y Astrofísica, v. 52, no. 2, p. 261-269.

© Copyright 2016: Instituto de Astronomía, Universidad Nacional Autónoma de México

The copyright holder has granted the permission for posting the article here.

Funding Information

GJF acknowledges support by NSF (1108928, 1109061, and 1412155), NASA (10- ATP10-0053, 10-ADAP10-0073, NNX12AH73G, and ATP13-0153), and STScI (HST-AR-13245, GO- 12560, HST-GO-12309, GO-13310.002-A, and HST- AR-13914). WJH acknowledges financial sup- port from DGAPA-UNAM through grant PAPIIT- IN11215. CRO’s participation was supported in part by HST program GO 12543. MP received partial support from CONACyT grant 241732.