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Recently, a suspicion arose that the free electrons in planetary nebulae(PNe) and HII regions might have non-thermal energy distributions. In thisscenario, a kappa index is introduced to characterize the electron energydistributions, with smaller kappa values indicating larger deviations fromMaxwell-Boltzmann distributions. Assuming that this is the case, we determinethe kappa values for a sample of PNe and HII regions by comparing theintensities of [OIII] collisionally excited lines and the hydrogen Balmer jump.We find the average kappa indices of PNe and HII regions to be 27 and 32,respectively. Correlations between the resultant kappa values and variousphysical properties of the nebulae are examined to explore the potential originof non-thermal electrons in photoionized gaseous nebulae. However, no positiveresult is obtained. Thus the current analysis does not lend to support to theidea that kappa-distributed electrons are present in PNe and HII regions.

astrophysical journal/the astrophysical journal

On the non-thermal kappa-distributed electrons in planetary nebulae and  HII regions: the kappa index and its correlations with other nebular  properties