Mid and Far IR properties of late-type galaxies in the Coma and A1367 clusters: ISOCAM and ISOPHOT observations

We present Mid (MIR) and Far (FIR) Infrared observations of 18 spiral/irreg ular galaxies belonging to the Coma and A1367 clusters, carried out with th e CAM and PHOT instruments on board the ISO satellite. Complementary photom etry from the UV to the Near Infrared (NIR) together with H alpha imaging, HI and (CO)-C-12 line measurements allow us to study the relationships betw een the IR emission and the star formation properties of these galaxies. Mo st of the resolved galaxies show extended MIR emission throughout their dis ks even where no H alpha emission is present. This suggests that the Aromat ic carriers can be excited by the general interstellar radiation field (ISR F), i.e. by visible photons. Only close to HII regions the UV photons are t he principal sources of Aromatic carrier excitation. However, when the UV r adiation field becomes intense enough these carriers can be destroyed. The average integrated 15/6.75 HII ratio of the observed galaxies is similar to 1, i.e. the typical value for the photodissociation regions (PDRs). This su ggests that, despite the high star formation rate (SFR) and the very lumino us HII regions of these galaxies, their integrated MIR emission is dominate d by PDR-like regions rather than HII-like regions. A cold dust component w ith average temperature similar to 22 K exists in most of the target galaxi es, probably arising from big dust grains (BGs) in thermal equilibrium with the ISRF. The contribution to the BGs heating from the ionizing stars decr eases with increasing wavelength. A warmer dust component whose emission do minates the spectrum between 20 and 100 mum is likely to exist. This is pro bably due to both Very Small Grains (VSGs) and warm BGs emission. The dust to gas ratio of the target galaxies is comparable to that of the solar neig hborhood. There is a weak trend between the dust total mass and both the at omic and molecular gas content. The MIR and FIR properties of the analyzed galaxies do not seem to be affected by the environment despite the fact tha t most of the targets are interacting with the Intra-Cluster-Medium.