Forty Years of Research on Isolated Galaxies
  Isolated galaxies have not been a hot topic over the past four decades. This
is partly due to uncertainties about their existence. Are there galaxies
isolated enough to be interesting? Do they exist in sufficient numbers to be
statistically useful? Most attempts to compile isolated galaxy lists were
marginally successful--too small number and not very isolated galaxies. If
really isolated galaxies do exist then their value becomes obvious in a
Universe where effects of interactions and environment (i.e. nurture) are
important. They provide a means for better quantifying effects of nurture. The
Catalog of Isolated Galaxies (CIG) compiled by Valentina Karachentseva appeared
near the beginning of the review period. It becomes the focus of this review
because of its obvious strengths and because the AMIGA project has increased
its utility through a refinement (a vetted CIG). It contains almost 1000
galaxies with nearest neighbor crossing times of 1-3Gyr. It is large enough to
serve as a zero-point or control sample. The galaxies in the CIG (and the
distribution of galaxy types) may be significantly different than those in even
slightly richer environments. The AMIGA-CIG, and future iterations, may be able
to tell us something about galaxy formation. It may also allow us to better
define intrinsic (natural) correlations like e.g. Fisher-Tully and FIR-OPTICAL.
Correlations can be better defined when the dispersion added by external
stimuli (nurture) is minimized or removed.
