Published online by Cambridge University Press: 26 May 2016
The planetary nebula luminosity function (PNLF) plays a key role in the distance ladder, as it is the only general purpose standard candle that is applicable to both Pop I and Pop II systems. We review the physics underlying the method, and compare its distances to distances obtained from Cepheids and surface brightness fluctuations (SBF). We show that PNLF distances agree with the geometric distances to the LMC and NGC 4258, and that, on a galaxy-by-galaxy basis, the relative PNLF, Cepheid, and SBF distances are in excellent agreement with no systematic trends. However, even though the PNLF and SBF methods are both calibrated by Cepheids, the PNLF distance scale is ~17% smaller than the SBF scale. We discuss this offset, and examine the possible causes of the discrepancy.