10 12 L starbursts and shocked molecular hydrogen in the colliding galaxies ARP 220 (=IC 4553) and NGC 6240.

March 1985 • 1985ApJ...290..116R

Authors • Rieke, G. H. • Cutri, R. M. • Black, J. H. • Kailey, W. F. • McAlary, C. W. • Lebofsky, M. J. • Elston, R.

Abstract • Infrared spectroscopy and photometry and optical spectroscopy of the exceedingly luminous interacting galaxies Arp 220 (= IC 4553) and NGC 6240 are presented. These galaxies are the sites of exceedingly powerful bursts of star formation, as shown by (1) the luminosity and extent of the stellar component seen near 2 microns; (2) the large population of red supergiants required to account for the depth of the stellar CO absorption; (3) the absorption and emission features in the spectrum longward of 3 microns; and (4) the extended luminosity source indicated by the spatial extent of the galaxies at 10 microns. Scaled-up models similar to those developed for less luminous starburst galaxies are consistent with this hypothesis. Arp 220 also appears to have an active nucleus, possibly of Seyfert type 2. Both galaxies also show strong lines from shocked molecular hydrogen, which may arise in the collisions of their interstellar clouds in an ongoing interaction.

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