Contents of: VI/111/./abstract/FCASOLI_ISOL_15.abs

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The environment exerts a major influence on the star formation activity
of spiral galaxies and on the nature and composition of their
interstellar medium. Interacting galaxies are known to have enhanced
star formation, while cluster galaxies are often highly deficient in
atomic hydrogen. ISO will provide a major progress with the study of the
Virgo cluster in the core program. But in order to have a quantitative
estimate of the effect of the environment in the observed properties of
Virgo objects, it is mandatory to construct a reference sample of
isolated galaxies. The Virgo core program uses as a reference galaxies
in the outskirts of the cluster. But we have no guarantee that they
behave as isolated galaxies. A reference sample will also be useful to
compare with galaxies in small groups or at cosmological distances.
We propose to observe a sample of 120 galaxies drawn from the
Karachenseva catalog of isolated galaxies. The sample objects will be
observed in the CII line at 158 microns with the LWS. This line is the
main coolant of the ISM, and probes both the photon-dominated regions
associated with massive-star formation and the diffuse atomic phase. An
important by-product of these observations will be the continuum
spectrum of the targets between 60 and 200 microns, which will allow us
to derive the cool dust content and to estimate the amount of gas in
these galaxies. 25 galaxies have not been detected by IRAS and will be
observed with PHOT at 60, 100 and 180 microns. In addition to the data
at other wavelengths, which we have already collected or are part of
ongoing observations (CO, HI, Halpha, radio continuum, optical colors,
NIR) the proposed observations will allow us to estimate the dust and
gas contents of isolated galaxies, their global star formation activity,
the relative contributions of the molecular and atomic phases in the
formation of the CII line, and to study the effect of the environment
on all these properties.