Planetary nebulae in the elliptical galaxy NGC 821: kinematics and
  distance determination
  Using a slitless spectroscopy method with the 8.2 m Subaru telescope and its
FOCAS Cassegrain spectrograph, we have increased the number of planetary nebula
(PN) detections and PN velocity measurements in the flattened elliptical galaxy
NGC 821. A comparison with the detections reported previously by the Planetary
Nebula Spectrograph (PN.S) group indicates that we have confirmed most of their
detections. The velocities measured by the two groups, using different
telescopes, spectrographs and slitless techniques, are in good agreement. We
have built a combined sample of 167 PNs and have confirmed the keplerian
decline of the line-of-sight velocity dispersion reported previously. We also
confirm misaligned rotation from the combined sample. A dark matter halo may
exist around this galaxy, but it is not needed to keep the PN velocities below
the local escape velocity as calculated from the visible mass. We have measured
the m(5007) magnitudes of 145 PNs and produced a statistically complete sample
of 40 PNs in NGC 821. The resulting PN luminosity function (PNLF) was used to
estimate a distance modulus of 31.4 mag, equivalent to 19 Mpc. We also
estimated the PN formation rate. NGC 821 becomes the most distant galaxy with a
PNLF distance determination. The PNLF distance modulus is smaller than the
surface brightness fluctuation (SBF) distance modulus by 0.4 mag. Our kinematic
information permits to rule out the idea that a shorter PNLF distance could be
produced by the contamination of the PNLF by background galaxies with emission
lines redshifted into the on-band filter transmission curve.
