A Simple Isolation Criterion based on 3D Redshift Space Mapping
  We selected a sample of galaxies, extremely isolated in 3D redshift space,
based on data from NED and the ongoing ALFALFA HI (21cm) survey. A simple
selection criterion was employed: having no neighbors closer than 300 km/s in
3D redshift space. The environments of galaxies, selected using this criterion
and NED data alone, were analyzed theoretically using a constrained simulation
of the local Universe, and were found to be an order of magnitude less dense
than environments around randomly selected galaxies. One third of the galaxies
selected using NED data alone did not pass the criterion when tested with
ALFALFA data, implying that the use of unbiased HI data significantly improves
the quality of the sample.
