RESOLVING THE ELECTRON TEMPERATURE DISCREPANCIES IN H ii REGIONS AND PLANETARY NEBULAE: κ-DISTRIBUTED ELECTRONS

By D. Nicholls, M. Dopita, R. Sutherland. 2012

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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 Maxwell–Boltzmann 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 kappa-distribution 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/71d6325029fe332e0d8696e910ec845bd0c2852b

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Citations in the corpus

A BUDGET AND ACCOUNTING OF METALS AT z ∼ 0: RESULTS FROM THE COS-HALOS SURVEY (2013, background): “…These systematic uncertainties are expected to be resolved by adopting a κ-distribution rather than a Maxwell-Boltzmann distribution for electron energies (Nicholls et al. 2012; Dopita et al. 2013). where M⋆ is in units of M⊙, and Moxy,ism Mg = mO × noxy µ̄mp × nH = 15.999 1.366 × noxy nH ,…”
Introduction to special section on Origins and Properties of Kappa Distributions: Statistical Background and Properties of Kappa Distributions in Space Plasmas (2015, background): “…2013; Livadiotis and McComas, 2011a, 2011b, 2012, 2013c, 2013d; Livadiotis, 2014]; and (iv) beyond the heliosphere, including HII regions [e.g., Nicholls et al., 2012], planetary nebula [e.g., Nicholls et al., 2012; Zhang et al., 2014], and supernova magnetospheres [e.g., Raymond et al., 2010].”
THE MASS–METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES (2012, background): “Recently, Nicholls et al. (2012) suggested that the electron energy distribution could be the cause of the temperature and metallicity discrepancies.”
NEW STRONG-LINE ABUNDANCE DIAGNOSTICS FOR H ii REGIONS: EFFECTS OF κ-DISTRIBUTED ELECTRON ENERGIES AND NEW ATOMIC DATA (2013, methodology): “(4) This equation can be evaluated analytically as a series of concave “banana curves” (see Nicholls et al. 2012, Figure 5).”
THE UNIVERSAL RELATION OF GALACTIC CHEMICAL EVOLUTION: THE ORIGIN OF THE MASS–METALLICITY RELATION (2014, background): “However, longstanding discrepancies between various metallicity diagnostics remain unresolved (e.g., Kudritzki et al. 2008; Bresolin et al. 2009; Kudritzki et al. 2012; Nicholls et al. 2012; Dopita et al. 2013).”
Deriving model-based Te-consistent chemical abundances in ionized gaseous nebulae (2014, background): “Other possible cause is found in the existence of chemical inhomogeneities (Tsamis & Péquignot 2005; Dors et al. 2013) or, more recently, in a possible asymmetric energy distribution for the free electrons in the ionised gas (the k distribution, Nicholls et al. 2012).”
THEORETICAL EVOLUTION OF OPTICAL STRONG LINES ACROSS COSMIC TIME (2013, methodology): “The Local Star-forming Abundance Sequence The Starburst99 (SB99) models that we use are described in detail in Levesque et al. (2010) and Nicholls et al. (2012).”
THE COSMIC BPT DIAGRAM: CONFRONTING THEORY WITH OBSERVATIONS (2013, methodology): “Mappings IV uses a Kappa temperature distribution which is more suitable for a turbulent ISM than a StefanBoltzmann distribution (Nicholls et al. 2012).”
Chemical abundances in high-redshift galaxies: a powerful new emission line diagnostic (2016, methodology): “Recently, Nicholls et al. (2012) have suggested that the electrons in H II regions are characterised by a κ−distribution in energy, rather than by a simple Maxwell-Boltzmann (M-B) distribution.”
New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies (2016, background): “Moreover, we are here considering the simple case of Maxwell-Boltzmann distributed electrons, while recent studies suggested that kdistributions could better represent the behavior of free electrons inside single Hii regions (Nicholls et al. 2012, 2013; Dopita et al. 2013).”