EDP Sciences
Free access
Issue
A&A
Volume 365, Number 2, January II 2001
Page(s) 11 - 27
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20000003


A&A 365, 11-27 (2001)
DOI: 10.1051/0004-6361:20000003

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

A. Contursi1,2,3 , A. Boselli4 , G. Gavazzi5 , E. Bertagna5 , R. Tuffs6 and J. Lequeux1 .

1  DEMIRM, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
2  Service d'Astrophysique, Centre d'Étude de Saclay, 91191 Gif-sur-Yvette, France
3  IPAC, JPL, Caletch, 100-22, Pasadena, CA 91125, USA
4  Laboratoire d'Astronomie Spatiale, BP 8, Traverse du Siphon, 13376 Marseille, France
5  Universitá di Milano - Bicocca, P.zza dell'Ateneo Nuovo 1, 20126 Milano, Italy
6  MPI für Kernphysik, Postfach 103980, 69117 Heidelberg, Germany

(Received 13 December 1999 / Accepted 28 September 2000)

Abstract
We present Mid (MIR) and Far (FIR) Infrared observations of 18 spiral/irregular galaxies belonging to the Coma and A1367 clusters, carried out with the CAM and PHOT instruments on board the ISO satellite. Complementary photometry from the UV to the Near Infrared (NIR) together with H$\alpha$ imaging, HI and 12CO line measurements allow us to study the relationships between the IR emission and the star formation properties of these galaxies. Most of the resolved galaxies show extended MIR emission throughout their disks even where no H$\alpha$ emission is present. This suggests that the Aromatic carriers can be excited by the general interstellar radiation field (ISRF), i.e. by visible photons. Only close to HII regions the UV photons are the principal sources of Aromatic carrier excitation. However, when the UV radiation field becomes intense enough these carriers can be destroyed. The average integrated $15/6.75 \mu$m ratio of the observed galaxies is $\sim $1, i.e. the typical value for the photodissociation regions (PDRs). This suggests that, despite the high star formation rate (SFR) and the very luminous HII regions of these galaxies, their integrated MIR emission is dominated by PDR-like regions rather than HII-like regions. A cold dust component with average temperature $\sim $22 K exists in most of the target galaxies, probably arising from big dust grains (BGs) in thermal equilibrium with the ISRF. The contribution to the BGs heating from the ionizing stars decreases with increasing wavelength. A warmer dust component whose emission dominates the spectrum between 20 and $100 \mu$m is likely to exist. This is probably 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 neighborhood. There is a weak trend between the dust total mass and both the atomic 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 that most of the targets are interacting with the Intra-Cluster-Medium.


Key words: galaxies: clusters: Coma; A 1367 -galaxies: ISM -galaxies: irregular - galaxies: spiral -infrared: galaxies

Offprint request: A. Contursi, contursi@ipac.caltech.edu

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