The Norma cluster (ACO3627) -- III. The Distance and Peculiar Velocity
  via the Near-Infrared Ks-band Fundamental Plane
  While Norma (ACO3627) is the richest cluster in the Great Attractor (GA)
region, its role in the local dynamics is poorly understood. The Norma cluster
has a mean redshift (z_CMB) of 0.0165 and has been proposed as the "core" of
the GA. We have used the Ks-band Fundamental Plane (FP) to measure Norma
cluster's distance with respect to the Coma cluster. We report FP photometry
parameters (effective radii and surface brightnesses), derived from ESO NTT
SOFI images, and velocity dispersions, from AAT 2dF spectroscopy, for 31
early-type galaxies in the cluster. For the Coma cluster we use 2MASS images
and SDSS velocity dispersion measurements for 121 early-type galaxies to
generate the calibrating FP dataset. For the combined Norma-Coma sample we
measure FP coefficients of a=1.465+/-0.059 and b=0.326+/-0.020. We find an rms
scatter, in log(central velocity dispersion) of 0.08 dex which corresponds to a
distance uncertainty of 28% per galaxy. The zero point offset between Norma's
and Coma's FPs is 0.154+/-0.014 dex. Assuming that the Coma cluster is at rest
with respect to the cosmic microwave background frame and z_CMB(Coma)=0.0240,
we derive a distance to the Norma cluster of 5026+/-160 km/s, and the derived
peculiar velocity is -72+/-170 km/s, i.e., consistent with zero. This is lower
than previously reported positive peculiar velocities for
clusters/groups/galaxies in the GA region and hence the Norma cluster may
indeed represent the GA's "core".
