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Astron. Astrophys. 333, L1-L4 (1998)

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1. Introduction

One of the most important recent discoveries in extragalactic astronomy has been the identification of a class of "infrared luminous galaxies" ([FORMULA] [FORMULA] 1011 [FORMULA]), which emit more energy in the infrared (5-500 µm) than in all other wavelengths combined (see review by Sanders & Mirabel, 1996). The trigger of the intense infrared emission appears to be the interaction/merger of molecular gas-rich spirals. Although the spectrum of the integrated radiation from these galaxies suggests that the bulk of the luminosity arises in regions that are heavily obscured by dust, the actual distribution of the mid-infrared emission with high spatial resolution is poorly known.

The Infrared Space Observatory (ISO, Kessler et al., 1996) offers unprecedented capabilities with respect to the Infrared Astronomical Satellite (IRAS). In the mid-infrared (5.5µm - 16.5 µm) the Infrared Space Observatory Camera (ISOCAM) provides an improvement in sensitivity of [FORMULA] 1000, and an increase in spatial resolution by a factor of [FORMULA] 60. Furthermore, observations with arcsec resolution in spectrophotometric mode with Circular Variable Filters (CVFs) permit us to infer the nature of the optically invisible stars that heat the dust and ionize the gas.

Here we present for the first time an image of NGC 4038/39 (Arp 244 = VV 245 = `The Antennae') in the LW3 (12 -17 µm) filter with [FORMULA] pixel field of view and compare it with the HST optical image. An extensive account of all the ISOCAM observations will be given in a forthcoming paper by Vigroux et al (1998). The Antennae is a prototype nearby merger system of two late-type spiral disk galaxies with nuclei separated by [FORMULA] 6.4 kpc. At a distance of 20 Mpc the total infrared luminosity measured by IRAS is 1011 [FORMULA], which is about five times the luminosity of the system at visual wavelengths. Molecular gas observations with a resolution of [FORMULA] (Stanford et al. 1990) showed that [FORMULA] 60% of the CO(1-0) emission from the overall system (Sanders & Mirabel 1985) is concentrated in the two nuclei and in an extended off-nuclear complex where the two disks overlap. The spatial distribution of the CO emission is consistent with the [FORMULA] 6 cm and [FORMULA] 20 cm radio continuum maps by Hummel & van der Hulst (1986).

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© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998