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 forplanetary nebulae (PN) in M87 and its surrounding halo. We show that theplanetary nebula luminosity function (PNLF) of M87's halo is unlike any PNLFobserved to date, with a shape that differs from that of the empirical law atthe 99.9% confidence level. In addition, we find that the PNLF of M87's outerhalo differs from that of the galaxy's inner regions at a high degree ofcertainty ($\sim 92%$). We show that both these effects are most likely due tothe existence of intracluster PN, many of which are foreground to M87. Theseintracluster objects explain the ``overluminous'' [O III] $\lambda 5007$sources previously identified by Jacoby, Ciardullo, & Ford (1990), and presentus with a new tool with which to probe the morphological and dynamicalproperties of the cluster. By modifying the maximum likelihood procedures ofCiardullo et al (1989a) and using an assumed M31 distance of 770 Kpc (Freedman& Madore 1990), we derive a distance modulus to M87 of $30.79 \pm 0.16$ ($14.4\pm 1.1$ Mpc).