R. Ciardullo et al., THE PLANETARY-NEBULA LUMINOSITY FUNCTION OF M87 AND THE INTRACLUSTER STARS OF VIRGO, The Astrophysical journal, 492(1), 1998, pp. 62-73
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.