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==> In this proposal, more time is being requested for FCASOLI.ISOL_14
==> Time for this proposal is to be transferred from FCASOLI.ISOL_14
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The environment exerts a major influence on spiral galaxies, their star
formation activity and the nature and composition of their interstellar medium.
ISO will provide a major progress in this field with the studies of the Virgo
and Coma clusters. But to draw quantitative estimates of these
environmental effects, it is mandatory to construct a reference sample of
isolated galaxies. A reference sample will also be useful to compare with
galaxies in small groups or at cosmological distances.
It is this reference sample
that we have proposed to build in our previous proposal (Star formation and
gas content in isolated galaxies:a reference sample). The goal was to observe
with the LWS the CII line at 158 microns in a large sample of isolated
galaxies.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. It is widely used as a star-formation tracer but
its exact relationship with the star-formation regions is still not well
understood. We will also get the continuum spectrum of the targets between
100 and 200 microns, which will allow us to estimate their cool dust and gas
content. In addition to the data at other wavelengths, 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. Our original sample was of 120
galaxies. Using the in-flight sensitivities, we had to reduce the sample to 67
galaxies, and out of 3 observed galaxies only one is detected. Thus we propose
to increase the observing time on the 35 best-known objects.