Astron. Astrophys. 324, L13-L16 (1997)

1. Introduction

The emission of the interstellar medium in the mid-IR is due to the Unidentified Infrared Emission Bands (UIBs) and in some conditions to the emission of very small, three-dimensional grains (Désert et al.   1990).

In order to understand better this emission, we have constructed a coherent program of observations with the Infrared Space Observatory (ISO), which includes a variety of Galactic objects which can be studied in details, objects in the Magellanic Clouds, larger regions in more distant galaxies like M 31, M 33, M 101, M 51 etc., then whole galaxies at larger distances in the Virgo cluster and the Coma supercluster. This paper is concerned with observations of a sample of the latter galaxies with ISOCAM through the two broad filters LW2 and LW3, which are centered respectively at 6.75 and 15 µm.

Section 2 describes the sample and the observations; Section 3 discusses the normalized mid-IR fluxes and colors in relation to the star-formation rate (SFR). Section 4 contains the conclusions.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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