Isolated galaxies are important since they probe the lowest density regimes
inhabited by galaxies. We define a sample of 36 nearby isolated early-type
galaxies for further study. Our isolation criteria require them to have no
comparable-mass neighbours within 2 B-band magnitudes, 0.67 Mpc in the plane of
the sky and 700 km/s in recession velocity. New wide-field optical imaging of
10 isolated galaxies with the Anglo-Australian Telescope confirms their
early-type morphology and relative isolation. We also present imaging of 4
galaxy groups as a control sample. The isolated galaxies are shown to be more
gravitationally isolated than the group galaxies. We find that the isolated
early-type galaxies have a mean effective colour of (B-R)_e = 1.54 +/- 0.14,
similar to their high-density counterparts. They reveal a similar
colour-magnitude relation slope and small intrinsic scatter to cluster
ellipticals. They also follow the Kormendy relation of surface brightness
versus size for luminous cluster galaxies. Such properties suggest that the
isolated galaxies formed at a similar epoch to cluster galaxies, such that the
bulk of their stars are very old. However, our galaxy modelling reveals
evidence for dust lanes, plumes, shells, boxy and disk isophotes in four out of
nine galaxies. Thus at least some isolated galaxies have experienced a recent
merger/accretion event which may have induced a small burst of star formation.
We derive luminosity functions for the isolated galaxies and find a faint slope
of -1.2, which is similar to the `universal' slope found in a wide variety of
environments. We examine the number density distribution of galaxies in the
field of the isolated galaxies.Comment: 16 pages, Latex, 17 figures, 6 tables, MNRAS in pres