Extragalactic Distances from Planetary Nebulae

Abstract

Abstract. The [O III] λ5007 planetary nebula luminosity function (PNLF) occupies an important place on the extragalactic distance ladder. Since it is the only method that is applicable to all the large galaxies of the Local Supercluster, it is uniquely useful for cross-checking results and linking the Population I and Population II distance scales. We review the physics underlying the method, demonstrate its precision, and illustrate its value by comparing its distances to distances obtained from Cepheids and the Surface Brightness Fluctuation (SBF) method. We use the Cepheid and PNLF distances to 13 galaxies to show that the metallicity dependence of the PNLF cutoff is in excellent agreement with that predicted from theory, and that no additional systematic corrections are needed for either method. However, when we compare the Cepheidcalibrated PNLF distance scale with the Cepheid-calibrated SBF distance scale, we find a significant offset: although the relative distances of both methods are in excellent agreement, the PNLF method produces results that are systematically shorter by ∼ 15%. We trace this discrepancy back to the calibration galaxies and show how a small amount of internal reddening can lead to a very large systematic error. Finally, we demonstrate how the PNLF and Cepheid distances to NGC 4258 argue for a short distance to the Large Magellanic Cloud, and a Hubble Constant that is ∼ 8% larger than that derived by the HST Key Project.

Evolution of planetary nebulae

“…(5), M * should reach a minimum for near-solar metallicities, contrarily to our findings. Following Ciardullo (2003), the results of Fig. 21 are the consequence of two competing factors: (1) since oxygen is one of the main coolants of a nebula, the flux in [O ] λ5007 increases only with the square root of the oxygen content (Jacoby 1989); and (2) the UV flux coming from the CSPN decreases with metallicity.…”

“…The importance of the PNLF for the cosmological distance ladder is fully described by e.g. Ciardullo (2003), and Jacoby et al (1999), Jacoby (1997), to whom we refer for all details.…”

“…At this stage, it is worth recalling and discussing the different interpretations to this issue that have been proposed in the recent literature, referring mostly to Jacoby (1996) and Ciardullo (2003), who provide two extended reviews on the PNLF as a distance indicator. Actually, the two reviews contain two different, perhaps complementary, explanations to the age-invariance of the cut-off brightness.…”

“…From the observational side, the evidences for a nearly constant maximum luminosity for PNe are numerous, as reviewed by e.g. Ciardullo (2003) and Jacoby (1997). The main points are: (1) m * does not significantly change with galactocentric radius in the galaxies M 31, M 81, NGC 4494 and NGC 5128, where significant population gradients should be present.…”

The Planetary Nebula Luminosity Function

“…(e.g., Ciardullo 2003;Hui et al 1993), internal tests within galaxy groups and clusters (e.g., Jacoby et al 1990;Ciardullo et al 1991), and external tests in galaxies with distances from Cepheid and surface brightness fluctuation measurements (Ciardullo et al 2002) yielded values of M * that were consistent to better than ∼ 10%. As Figure 1 illustrates, the only systematic trend was a slight fading of M * at low metallicity -a fading that was entirely consistent with the expected response of a set of nebulae to lower oxygen abundance (Ciardullo & Jacoby 1992;Dopita et al 1992;Ciardullo et al 2002).…”