  The aim of this work is to study the effects of environment on the growth in
size of galaxies. We examine the stellar mass-size relation for a sample of
isolated galaxies interpreted as stellar systems where evolution has been
mainly governed by internal processes. Effects of environment on the stellar
mass-size relation are evaluated by comparing our results with samples of less
isolated early- and late-type galaxies, as well as, for the first time,
different spiral subtypes. We find no difference in the stellar mass-size
relation for very isolated and less isolated early-type galaxies. We find that
late-type isolated galaxies are ~1.2 times larger than less isolated objects
with similar mass. Isolated galaxies and comparison samples were divided into 6
morphological ranges (E/S0, Spirals, Sb, Sbc, Sc, and Scd-Sdm) and 5 stellar
mass bins between log(M*)=[9,11.5]. In all cases the relation is better defined
and has less scatter for the isolated galaxies. We find that as the
morphological type becomes later the galaxy size (for a fixed stellar mass)
becomes larger. For the lowest stellar mass bins log(M*)=[9,10] we find good
agreement between sizes of AMIGA and comparison spirals. The isolated spiral
galaxies in the high stellar mass bins log(M*)=[10,11] tend to be larger than
less isolated galaxies. This difference in size is found for all spiral
subtypes and becomes larger when we compare fully isolated galaxies with
galaxies having 2 or more satellites (neighbors within 3 magnitudes of
difference at a distance less than 250 kpc from the galaxy). Our results
suggest that massive spiral galaxies located in low density environments, both
in terms of major companions and satellites, have larger sizes than samples of
less isolated galaxies. Hence the environment has played a role in the growth
in size of massive spiral galaxies.
