THE PLANETARY-NEBULA LUMINOSITY FUNCTION OF M87 AND THE INTRACLUSTER STARS OF VIRGO

We present the results of a wide-field [O III] lambda 5007 survey for planetary nebulae (PN) in M87 and its surrounding halo. In all, we ide ntify 338 PN candidates in a 16' x 16' field around the galaxy; 187 of these objects are in a statistical sample that extends to m(5007) = 2 7.15. We show that the planetary nebula luminosity function (PNLF) of M87's halo is unlike any PNLF observed to date, with a shape that diff ers from that of the empirical law at the 99.9% confidence level. In a ddition, we find that the PNLF of M87's outer halo differs from that o f the galaxy's inner regions at a high degree of certainty (similar to 92%). We show that both these effects are most likely due to the exis tence of intracluster PN, many of which are foreground to M87. These i ntracluster objects explain the ''overluminous'' [O III] lambda 5007 s ources previously identified by Jacoby, Ciardullo, & Ford and present us with a new tool with which to probe the morphological and dynamical properties of the cluster. By modifying the maximum likelihood proced ures of Ciardullo et al. to take into account the presence of ''field objects'' and using, an assumed M31 distance of 770 Kpc (Freedman & Ma dore) with a Burstein & Heiles reddening law, we derive a distance mod ulus to M87 of 30.79 +/- 10.16 (14.4 +/- 1.1 Mpc). This value is in ex cellent agreement with the previous survey of Jacoby, Ciardullo, & For d and contradicts the assertion of Bottinelli et al. and Tammann that the PNLF distance to Virgo has been underestimated as a result of inad equate survey depth.