Formation, Evolution and Properties of Isolated Field Elliptical
  Galaxies
  [Abridged] We study the properties, evolution and formation mechanisms of
isolated field elliptical galaxies. We create a mock catalogue of isolated
field elliptical galaxies from the Millennium Simulation Galaxy Catalogue, and
trace their merging histories. The formation, identity and assembly redshifts
of simulated isolated and non-isolated elliptical galaxies are studied and
compared. Observational and numerical data are used to compare age, mass, and
the colour-magnitude relation. Our results, based on simulation data, show that
almost seven per cent of all elliptical galaxies brighter than -19mag in B-band
can be classified as isolated field elliptical galaxies. Isolated field
elliptical galaxies show bluer colours than non-isolated elliptical galaxies
and they appear younger, in a statistical sense, according to their mass
weighted age. Isolated field elliptical galaxies also form and assemble at
lower redshifts compared to non-isolated elliptical galaxies. About 46 per cent
of isolated field elliptical galaxies have undergone at least one major merging
event in their formation history, while the same fraction is only about 33 per
cent for non-isolated ellipticals. The mean time of the last major merging is z
= 0.6 or 6 Gyrs ago for isolated ellipticals, while non-isolated ellipticals
experience their last major merging significantly earlier at z = 1.1 or 8 Gyrs
ago. After inspecting merger trees of simulated isolated field elliptical
galaxies, we conclude that three different, yet typical formation mechanisms
can be identified: solitude, coupling and cannibalism. Our results also predict
a previously unobserved population of blue, dim and light galaxies that fulfill
observational criteria to be classified as isolated field elliptical galaxies.
This separate population comprises about 26 per cent of all IfEs.
