The planetary nebula system of M33

We report the results of a photometric and spectroscopic survey for planetary nebulae (PNs) over the entire body of the Local Group spiral galaxy M33. We use our sample of 152 PNs to show that the bright end of the galaxy's [O III] lambda5007 planetary nebula luminosity function (PNLF) has the same sharp cutoff seen in other galaxies. The apparent magnitude of this cutoff, along with the IRAS DIRBE foreground extinction estimate of E(B-V) 0.041, implies a distance modulus for the galaxy of (m-M)(0) 24.86(-0.11)(+0.07) (0.94(-0.05)(+0.03) Mpc). Although this value is similar to15% larger than the galaxy's Cepheid distance, the discrepancy likely arises from differing assumptions about the system's internal extinction. Our photometry, which extends more than 3 mag down the PNLF, also reveals that the faint end of M33's PNLF is nonmonotonic, with an inflection point similar to2 mag below the PNLF's bright limit. We argue that this feature is due to the galaxy's large population of high core mass planetaries and that its amplitude may eventually be a useful diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33's PN population rotates along with the old disk, with a small asymmetric drift of similar to10 km s(-1). Remarkably, the population's line-of-sight velocity dispersion varies little over similar to4 optical disk scale lengths, with sigma(rad) similar to 20 km s(-1). We show that this is due to a combination of factors, including a decline in the radial component of the velocity ellipsoid at small galactocentric radii and a gradient in the ratio of the vertical to radial velocity dispersion. We use our data to derive the dynamical scale length of M33's disk and the disk's mass-to-light ratio. Our most likely solution suggests that the surface mass density of M33's disk decreases exponentially, but with a scale length that is similar to2.3 times larger than that of the system's IR luminosity. The large scale length also implies that the disk's V-band mass-to-light ratio changes from M/L-V similar to 0.3 in the galaxy's inner regions to M/L-V similar to2.0 at similar to9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data.