ISOPHOT 3 to 240 micron Spectral Energy Distribution of NGC 6240
(Hi-Res: Postscript)
NGC 6240 is a tightly interacting system of two galaxies which will eventually merge. The most important signatures of this interaction are a strongly disturbed and irregular body with extended tails and two nuclei separated in projection by 2", or about 2000 light years.
It is very likely that the collision of interstellar clouds triggers the violent formation of massive hot stars which heat the interstellar medium considerably more than in quiescent galaxies. This is confirmed by the ISOPHOT observations.
Further details of these observations can be found in the Astronomy and Astrophysics letter A&A, 325/3, L21-L24, 1997:
"Infrared spectral energy distributions of the interacting galaxies Arp 244, NGC 6240, and Arp 220".
U. Klaas, M. Haas, I. Heinrichsen and B. Schulz.