RESOLVING THE ELECTRON TEMPERATURE DISCREPANCIES IN H II REGIONS AND PLANETARY NEBULAE: Κ-Distributed ELECTRONS

Abstract

The measurement of electron temperatures and metallicities in H ii regions and Planetary Nebulae (PNe) has-for several decades-presented a problem: results obtained using different techniques disagree. What is worse, they disagree consistently. There have been numerous attempts to explain these discrepancies, but none has provided a satisfactory solution to the problem. In this paper, we explore the possibility that electrons in H ii regions and PNe depart from a M-B equilibrium energy distribution. We adopt a "κ-distribution" for the electron energies. Such distributions are widely found in solar system plasmas, where they can be directly measured. This simple assumption is able to explain the temperature and metallicity discrepancies in H ii regions and PNe arising from the different measurement techniques. We find that the energy distribution does not need to depart dramatically from an equilibrium distribution. From an examination of data from H ii regions and PNe it appears that κ 10 is sufficient to encompass nearly all objects. We argue that the kappadistribution offers an important new insight into the physics of gaseous nebulae, both in the Milky Way and elsewhere, and one that promises significantly more accurate estimates of temperature and metallicity in these regions.

Starburst–AGN mixing – II. Optically selected active galaxies

“…MAPPINGS IV incorporates new atomic data and Maxwell collision strengths as well as a non-thermal (κ) electron temperature distribution (described in detail in Nicholls et al 2012Nicholls et al , 2013. The defining feature of this distribution is that the fraction of hot electrons can be varied using the κ value.…”

“…Since then, κ distributions have also been identified in the magnetospheres of all the gas giant planets as well as Mercury, Titan and Io (see references in Pierrard & Lazar 2010) and at the interface between the solar heliosheath and the surrounding interstellar medium (Livadiotis et al 2011). These κ distributions arise due to external energy input which prevents the system from relaxing to a classical Maxwell-Boltzmann distribution (see discussion in Nicholls et al 2012). Applying the κ distribution to extragalactic H II regions resolves the long standing discrepancy between electron temperatures calculated using direct, recombination line and strong line ratio methods (Nicholls et al 2012).…”

A framework for empirical galaxy phenomenology: the scatter in galaxy ages and stellar metallicities

“…This effect is due to the sensitivity of metal lines to the electron temperature and ex-citation/ionization structure of HII regions, which in turn depend onṀSFR (e.g., Peña-Guerrero et al 2012;Andrews & Martini 2013). Moreover, incorrect parameterization of these properties can introduce systematic uncertainties into the derived metallicity measurement, though Nicholls et al (2012) and Dopita et al (2013) show that adding a high-energy tail to the standard Maxwell-Boltzmann distribution of electron energies can improve temperature estimates and reconcile seemingly discrepant indicators.…”

The slow flow model of dust efflux in local star-forming galaxies

“…Peimbert (1967) points out that temperature fluctuations may lead to systematic underestimates of the metallicity. More recently, the assumption that HII regions are in thermodynamic equilibrium has also been challenged (Nicholls et al 2012Dopita et al 2013). These authors argue that a breakdown of the assumption of equilibrium leads to an underestimate of the abundance, particularly in metal-rich HII regions.…”

“…Astrophysical plasmas where in situ measurements of electron energies can be made have nonequilibrium energy distributions (Nicholls et al 2012). This suggests that perhaps metallicities determinations based on theoretical models (i.e.…”