Astron. Astrophys. 356, L83-L87 (2000)

1. Introduction

NGC 4038/39 (Arp 244, distance 21 Mpc) is the prototype of an interacting system with spectacular tidal tails, "The Antennae". While the stars in such interacting systems undergo elastic collisions and the resulting shape is best outlined in the optical (e.g. the HST image in Whitmore & Schweizer 1995), the interstellar matter suffers inelastic collisons. Hence, it will be differently distributed than the stars. Also, bursts of star formation occur: Tidal forces shock and compress the gas so that it finally collapses into new stars. Exceptional star formation knots have been observed in the overlap region between the two nuclei of NGC 4038/39 with ISOCAM at 7-15 µm, sensitive to warm dust (Mirabel et al. 1998). The brightest knot which even outshines both nuclei, is inconspicuous at optical wavelengths. The HST image rather shows a pronounced dust lane between the two reddened nuclei. Thus, the starbursts are hidden behind enormous amounts of dust.

Based on 10-200 µm ISO photometry the luminosity of warm and cold dust emission has been determined for the total galaxy (6.4 10¹⁰ , Klaas et al. 1997), and Kuiper Airbourne Observatory 100 and 160 µm maps, though with limited spatial resolution, suggest a major contribution from the overlap region (Bushouse et al. 1998). Here, we resolve the distribution of the cold dust (T 40 K) showing up between 60 and 850 µm using SCUBA (Holland et al. 1999) at the JCMT and ISOPHOT (Lemke et al. 1996) onboard ISO (Kessler et al. 1996). The dust serves as an excellent tracer of interstellar matter. Its luminosity and temperature provide clues to heating processes and evolutionary states: Of particular interest in this early stage of merging galaxies is, how far heating by starbursts has already onset or whether dust cloud complexes are still in a pre-starburst phase.

© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000
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