We report the results of a photometric and spectroscopic survey for planetary nebulae (PNe) in the Local Group spiral galaxy M33. We use our sample of 152 PNe to derive an [O III] planetary nebula luminosity function (PNLF) distance of (m-M)_0 = 24.86^+0.07-0.11 (0.94^+0.03-0.05 Mpc). Although this value is ~ 15% larger than the galaxys Cepheid distance, the discrepancy likely arises from differing assumptions about the systems internal extinction. Our photometry (which extends >3 mag down the PNLF), also reveals that the faint-end of M33s PN luminosity function is non-monotonic, with an inflection point ~2 mag below the PNLF cutoff. We argue that this feature is due to the galaxys large population of high core-mass planetaries, and that its amplitude may eventually be useful as a diagnostic for studies of stellar populations. Fiber-coupled spectroscopy of 140 of the PN candidates confirms that M33s PN population rotates along with the old disk, with a small asymmetric drift of ~ 10km/s. Remarkably, the populations line-of-sight velocity dispersion varies little over ~4 optical disk scale lengths, with sigma_{rad}~20km/s. 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 show that the mass scale length of M33s disk is ~2.3 times larger than that of the systems IR luminosity and that the disks V-band mass-to-light ratio changes from M/L_V ~0.3 in the galaxys inner regions to M/L_V ~2.0 at ~9 kpc. Models in which the dark matter is distributed in the plane of the galaxy are excluded by our data. (abridged)
Download