A coordinated study of galaxies in the Virgo cluster

scientific abstract: this proposal is a part of a coherent program to study the interstellar medium in selected normal (noninteracting, nonstarburst, nonagn) galaxies in the near to farir in coordination with the phot and sot consortia. the present part of the program consists in imaging a complete sample of spiral, irregular and blue compact galaxies in the virgo cluster in two filters: lw 2 (5.08.0 micrometers) and lw 3 (1218 micrometers). the emission in lw 2 will be dominated by ir emission bands and that in lw 3 by hot dust. the nature and physics of both components is not well understood and the iras 12 micrometer filter did not allow a clear separation between them. however iras and other observations have shown that the intensity of both are affected by the uv radiation field and by metallicity, and also that the ir band carriers (pahs or related large molecules) are easily frozen on bigger grains or liberated from them. together with the other coordinated iso observations and complementary goundbased observations they will yield a more complete picture of the physics of dust and possibly a full understanding of the thermal balance of dust and gas in galaxies. as some properties of galaxies e.g. their hi content depend on their environment the proposed observations of a complete sample of galaxies in the center and in the outskirts of the virgo cluster will allow mapping and statistical studies of the global properties of galaxies (both spiral and irregular) in the midir as well as a study of the effect of the environment. these galaxies will also serve as templates for iso studies of clusters at large distances (see the corresponding iso coreprogramme proposals). all the selected virgo galaxies will also be observed by phot (phot guaranteed time) and the brighter half by lws in the 158 micrometer line of ionized carbon (sot guaranteed time). observation summary: full imaging of the target galaxies truncated [truncated!, Please see actual data for full text]