The Planetary Nebula Luminosity Function of M87 and the Intracluster Stars of Virgo

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Abstract
We present the results of a wide-field [O III] λ5007 survey for planetary nebulae (PN) in M87 and its surrounding halo. In all, we identify 338 PN candidates in a 16' × 16' field around the galaxy; 187 of these objects are in a statistical sample that extends to m5007 = 27.15. We show that the planetary nebula luminosity function (PNLF) of M87's halo is unlike any PNLF observed to date, with a shape that differs from that of the empirical law at the 99.9% confidence level. In addition, we find that the PNLF of M87's outer halo differs from that of the galaxy's inner regions at a high degree of certainty (~92%). We show that both these effects are most likely due to the existence of intracluster PN, many of which are foreground to M87. These intracluster objects explain the "overluminous" [O III] λ5007 sources 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 procedures of Ciardullo et al. to take into account the presence of "field objects" and using an assumed M31 distance of 770 Kpc (Freedman & Madore) with a Burstein & Heiles reddening law, we derive a distance modulus to M87 of 30.79 ± 0.16 (14.4 ± 1.1 Mpc). This value is in excellent agreement with the previous survey of Jacoby, Ciardullo, & Ford and contradicts the assertion of Bottinelli et al. and Tammann that the PNLF distance to Virgo has been underestimated as a result of inadequate survey depth.
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