Distances from the Planetary Nebulae Luminosity Function

Abstract

The distances obtained from the planetary nebulae luminosity function (PNLF) are compared with distances from the surface brightness fluctuation (SBF) method and with cepheid distances. The recently recalibrated SBF distances are systematically larger than their PNLF counterparts for distances above 10 Mpc. Both PNLF and SBF distances agree with cepheid distances much better than they agree with each other. Looking only at the comparison with cepheids it would seem that the PNLF and SBF distances are good to about ±0.2 mag in distance moduli for distances above 10 Mpc. But the existence of unexplained systematic differences between PNLF and SBF distances suggests that it may be better to increase the uncertainties to about ±0.3 mag until the situation is clarified. A Monte Carlo method to produce numerical simulations of the PNLF is described. Some possible shortcomings of the PNLF method (including the existence of intracluster planetary nebulae in the Virgo and Fornax clusters) are discussed, but none of them appears to provide a promising explanation for the systematic differences with the SBF method. Finally, some comments are added about the shape of the PNLF.