Published in "The Extragalactic Distance Scale", eds. M Livio, M. Donahue and N. Panagia, Cambridge University Press 1997.

For a postscript version of the article, click here.

**Abstract.** The planetary nebula luminosity function (PNLF)
technique for determining distances to galaxies
now has been applied to 34 galaxies, including 6 in the Virgo cluster
and 3 in the Fornax cluster. Of these, 16 galaxies are late-type or
spirals and presumably contain Cepheid variables
useful for verifying the PNLF method. For 7 of these galaxies, Cepheid
distances exist; the PNLF distances agree with the Cepheid distances
within the dispersion of 8% and within a zero-point offset of 1%.

In addition, 3 small groups were studied (NGC 1023, Leo I, and Coma I) where both spiral and elliptical distances were obtained to investigate the magnitude of any systematic dependence on spiral versus elliptical Hubble type. None was found. Since the PNLF method agrees well with the Cepheid system, and there is no measurable dependence on Hubble type, it follows that PNLF distances to the ellipticals in Virgo and Fornax also are on the Cepheid scale. This conclusion is strengthened by the Cepheid distances to several Virgo galaxies and the recent determination of a Cepheid distance to Fornax.

Challenges to the PNLF method by Bottinelli et al. (1991) and Tammann (1992) are demonstrated to be incorrect. In particular, the allegation that the Virgo distances suffer from inadequate survey depth is rendered baseless with recent observations that extend the PNLF beyond the power law regime and well into the plateau region. Using the new observations of 320 PN, bootstrap tests show that any sample size effect is smaller than 3%.

Finally, a simple thought experiment is presented whereby M87 is placed
at 22 Mpc as argued
by those favoring *H*_{0} ~ 50. The consequent luminosities
for observed planetary nebulae are
inconsistent with stellar evolution theory, thereby invalidating the
assumption of a distance greater than ~ 17 Mpc; alternatively, a drastic
change in stellarevolution theory is required.

**Table of Contents**

- INTRODUCTION
- WHAT MAKES A GOOD DISTANCE INDICATOR?
- SOME NEW INSIGHTS
- SUMMARY OF PNLF DISTANCES
- SPIRALS
- THE SPIRAL-ELLIPTICAL CONNECTION
- DETAILS OF NEW M87 PNLF STUDIES
- A deep PNLF distance contradicts the challenges
- Sample size effects are small
- Bright PN in M87's halo
- CAN M87 REALLY BE AT 22 MPC?
- SOME IMPORTANT DISTANCES
- CONCLUSIONS
- REFERENCES