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

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Letter to the Editor

The cold dust concentrations in the colliding galaxies NGC 4038/39 *

M. Haas 1, U. Klaas 1, I. Coulson 2, E. Thommes 1,3 and C. Xu 4

1 Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
2 Joint Astronomy Centre, 660 N. Aohuku Place, University Park, Hilo 96720, Hawaii, USA
3 Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
4 Infrared Processing and Analysis Center, Jet Propulsion Laboratory, Caltech 100-22, Pasadena, CA91125, USA

Received 3 March 2000 / Accepted 18 March 2000


SCUBA 450 and 850 µm maps of the Antennae Galaxy resolve the nuclei of NGC 4038/39 and two prominent regions in the overlap area of the galaxy disks. They coincide excellently with bright emission peaks seen on 15 µm, 6 cm and CO maps. ISOPHOT 60 and 100 µm maps reveal that the overlap area and the NGC 4038 nucleus are also responsible for the bulk of the far-infrared emission. In addition to the prominent emission from dust at a temperature of about 30 K, typical for active starburst galaxies, cold dust at temperatures below 20 K is found like in quiescent galaxies and dense cloud complexes. Thus, the observations suggest a common phenomenon for merging galaxies: besides the warm dust heated by active starbursts they possess simultaneously dense concentrations of cold dust which are presumably in a pre-starburst phase. The dust mass in the two overlap region knots is about 107 [FORMULA] which comprises a considerable fraction of the typical dust content of a whole spiral galaxy. Such a high concentration could be explained by an initial inelastic collision of clouds which loose their angular momentum and serve as concentrating kernels into which the other clouds rotating in the disks are running. The two submm knots seem to comprise independent kernels, since they are too far separated to be mutually triggered.

Key words: galaxies: fundamental parameters – galaxies: individual: – galaxies: interactions – galaxies: photometry – infrared: galaxies

* Based on observations at the James Clerk Maxwell Telescope JCMT and with the Infrared Space Observatory ISO.

Send offprint requests to: M. Haas (haas@mpia-hd.mpg.de)

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© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000