Contents of: VI/111/./abstract/FMACCHET_P2_3.abs

The following document lists the file abstract/FMACCHET_P2_3.abs from catalogue VI/111.
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We propose to carry out broad-band imaging with ISOCAM of a sample of nearby
elliptical galaxies for which we have already obtained an accurate mapping of
the dust absorption and of the line-emitting (Halpha+NII), warm gas component
from optical data, as a part of our now completed ESO Key Programme "Towards a
Physical Classification of Early-Type Galaxies". It is now clear that as much
as 80% of the ellipticals contain dust, while about 53% show warm ionized gas.
Puzzingly though, the amount of dust mass inferred from optical observations is
usually small, an order of magnitude less than the estimate from IRAS. Also,
dust and gas are usually associated and do not follow the general stellar
distribution, strongly suggesting an external origin for them. To tackle the
important problem of the origin and evolution of the ISM in ellipticals on a
quantitative basis, we propose to image at mid-IR wavelengths through the LW1,
LW3 and LW7 filters to map the distribution of the warm dust component
(including the silicate band) and to derive its physical properties, such as
temperature and mass. By correlating these properties with the other
characteristics of the host galaxies, such as the radio and X-ray luminosities,
optical dust lanes, Halpha emission and distribution, we will directly test the
hypothesis that dust and gas have an external origin and that a fraction of the
warm component, responsible for the mid-IR diffused emission, originates in the
winds of evolved stars. This will also provide crucial information about the
relevant physical processes taking place in the ISM. For instance, it has been
suggested that the X-ray coronae of elliptical galaxies provide a very hostile
environment for dust and so by mapping the intensity of dust emission we will
be able to probe whether there is dust formation and destruction at work. The
high quality of our dust absorption and emission-line images coupled with the
excellent resolution capabilities in the mid-IR of ISOCAM will enable us to
investigate the relationship between the optical colors (V-R) and the presence
of dust, its association with the optical dust lanes and its co-spatiality with
the gas. ISO is the only facility offering mid-IR imaging capabilities with a
resolution high enough to allow meaningful comparisons with optical images.

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