  Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.
