A Comparison of the Planetary Nebula Luminosity Function and Surface Brightness Fluctuation Distance Scales
Two of the best techniques for measuring distances greater than ∼3 Mpc are the planetary nebula luminosity function (PNLF) and the surface brightness fluctuation (SBF) method. We compare the results of both methods and analyze the internal and external errors associated with the measurements. We find that the PNLF distances are systematically larger than the SBF distances by 0.07±0.03 mag, but this error can be entirely attributed to uncertainties in the Local Group calibrations which both methods employ. After correcting for this effect, we find the random scatter in the difference between the PNLF and SBF distance determinations, Δ = (m-M)SBF - (m-M)PNLF = 0.17 mag, is in exact agreement with that predicted from the internal uncertainties of the methods. We show that Δ is not measurably correlated with such parameters as galaxy color, metallicity, specific PN density, and specific globular cluster frequency, but does correlate slightly with galactic absolute B magnitude. We discuss the reality of this correlation and show that the trend is not important for extragalactic distance applications.