AAS 195th Meeting, January 2000
Session 11. Calibrating the Distance Scales
Display, Wednesday, January 12, 2000, 9:20am-6:30pm, Grand Hall

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[11.03] Planetary Nebula Luminosity Function Distances to M 33, NGC 2403 and NGC 3627 and a Comparison to the Cepheid Distance Scale

R.E. Kuzio, R. Ciardullo, J.J. Feldmeier (Penn State), G.H. Jacoby (KPNO)

We report the results of an [O~III] \lambda 5007 survey for planetary nebulae (PNe) in three spiral galaxies: M33 (NGC~598), NGC~2403, and NGC~3627. By comparing on-band/off-band [O~III] \lambda 5007 images with images taken in H\alpha, we identify 58, 40, and 73~PNe candidates in each galaxy, respectively. From these data, an adopted M31 distance of 770~kpc, and the empirical planetary nebula luminosity function (PNLF), we derive preliminary distances to M33, NGC~2403, and NGC~3627 of .85+0.07-0.10, 3.26+0.27-0.30, 10.41+0.68-0.67~Mpc.

With the addition of M33, NGC~2403, and NGC~3627, there are now 11 galaxies with both PNLF and Cepheid distance measurements: 4 galaxies in the Local Group (the SMC, the LMC, M31, and M33), two M81 group galaxies (M81 and NGC~2403), two Leo~Group galaxies (M96 and NGC~3627), and three others (M101, NGC~300, and NGC~5253). We examine the systematic behavior between the PNLF and Cepheid distance estimates, and show that for large, metal-rich galaxies, the two distance scales are in excellent agreement. However, we also show that there is a systematic offset between the two scales for low-luminosity, metal-poor galaxies. For these objects, the PNLF method gives distances that are ~ 10% larger than the distances derived from Cepheids. We model this behavior, and provide a metallicity correction for the PNLF technique.

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