Re-examining the Bayesian colour excess estimation for the local star-forming galaxies observed in the HETDEX Pilot Survey

Abstract

In my previous reanalysis of the local star-forming galaxies observed in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) pilot survey, I reported that the overestimation of E(B - V), hence the star formation rate (SFR), undermined the claim of new galaxy population discovery in the original study. Herein, I re-examine whether the E(B - V) overestimation problem can be alleviated in the Bayesian parameter estimation framework by adopting scientifically motivated new priors. I modelled the emission-line fluxes of galaxies using the strong-line method and four model parameters-metallicity 12 + log (O/H), nebula emission-line colour excess E(B - V), intrinsic [O III] $\lambda$5007 line flux and intrinsic [N II] $\lambda$6584 line flux. Based on mock-data tests, I found that all input values can be recovered within and around the 1-$\sigma$ credible interval by adopting suitable priors for the intrinsic [O III] $\lambda$5007 and [N II] $\lambda$6584 line fluxes: the inverse gamma distribution reflecting the logical constraint that an intrinsic emission-line flux must exceed the observed (reddened) emission-line flux. The mock-data tests were performed for two metallicity calibrations, three colour excess input values [E(B - V) = 0.1, 0.3 and 0.5] and two metallicity input values [12 + log (O/H) = 8.0 and 8.5]. I also found that the new prior can diminish the SFR overestimation eightfold. This study demonstrates how the Bayesian parameter estimation can achieve more accurate estimates with no further observations when the likelihood does not constrain the model parameters correctly.

10 pages, 6 figures, MNRAS in press, online supplementary data are included in the source file

References in corpus (8)

• The Mass-Metallicity and the Fundamental Metallicity Relation revisited on a fully Te-based abundance scale for galaxies
• New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies
• emcee v3: A Python ensemble sampling toolkit for affine-invariant MCMC
• Markov Chain Monte Carlo Methods for Bayesian Data Analysis in Astronomy
• Bayesian Galaxy Shape Measurement for Weak Lensing Surveys -I. Methodology and a Fast Fitting Algorithm
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• The HETDEX Instrumentation: Hobby-Eberly Telescope Wide Field Upgrade and VIRUS
• Revisiting the Local Star-Forming Galaxies Observed in the HETDEX Pilot Survey