Planetary nebulae in the elliptical galaxy NGC 4649 (M 60): kinematics
  and distance redetermination
  Using a slitless spectroscopy method with (a) the 8.2 m Subaru telescope and
its FOCAS Cassegrain spectrograph, and (b) the ESO Very Large Telescope (VLT)
unit 1 (Antu) and its FORS2 Cassegrain spectrograph, we have detected 326
planetary nebulae (PNs) in the giant Virgo elliptical galaxy NGC 4649 (M 60),
and we have measured their radial velocities. After rejecting some PNs more
likely to belong to the companion galaxy NGC 4647, we have built a catalog with
kinematic information for 298 PNs in M 60. Using these radial velocities we
have concluded that they support the presence of a dark matter halo around M
60. Based on an isotropic, two-component Hernquist model, we estimate the dark
matter halo mass within 3$R_{\rm e}$ to be 4$\times10^{11} M_{\odot}$, which is
almost one half of the total mass of about $10^{12} M_{\odot}$ within 3$R_{\rm
e}$. This total mass is similar to that estimated from globular cluster,
XMM-Newton and Chandra observations. The dark matter becomes dominant outside.
More detailed dynamical modeling of the PN data is being published in a
companion paper. We have also measured the $m$(5007) magnitudes of many of
these PNs, and built a statistically complete sample of 218 PNs. The resulting
PN luminosity function (PNLF) was used to estimate a distance modulus of
30.7$\pm$0.2 mag, equivalent to 14$\pm$1 Mpc. This confirms an earlier PNLF
distance measurement, based on a much smaller sample. The PNLF distance modulus
remains smaller than the surface brightness fluctuation (SBF) distance modulus
by 0.4 mag.
