Near-Infrared Images and Color Maps of ARP 220

February 1992 • 1992AJ....103..413M

Authors • Mazzarella, J. M. • Soifer, B. T. • Graham, J. R. • Hafer, C. I. • Neugebauer, G. • Matthews, K.

Abstract • Near-infrared images (λ= 1.3-3.7 microns) are presented for the nuclear region of Arp 220. Color maps in J - H and H - K reveal steep gradients, and the two nuclei previously detected at 20 cm and 2.2 microns appear on the J - H image as peaks separated by 1". Hot dust emission (T ~ 1000 K) at 3.7 microns and extremely red J - H and H - K colors are found for both nuclei. The increasingly red colors approaching the center of the galaxy are explained most naturally by a mixture of extinction and emission by increasing amounts of hot dust. The near- infrared emission is consistent with a circumnuclear starburst extending to a radius of ~ 1.5 kpc (4") from the nuclei; further from the center the colors are consistent with a normal late-type stellar population. inside a radius of 1 kpc the color maps show a NE-SW elongation that aligns with the concentration of molecular gas seen in CO images. The SW portion of this region is coincident with a protrusion in radio continuum images, likely due to synchrotron emission from supernovae remnants with roughly the same spatial distribution as the hot dust. The observed 3.7 micron luminosity, when corrected for nuclear extinction determined by 10 micron silicate absorption measurements and normalized by the bolometric luminosity, is consistent with UV-excess quasars and is ~10 times greater than that found in infrared luminous starburst galaxies. However, the observed nuclear K - L' color is not different from the nucleus of M82, so the current data cannot rule out a nuclear starburst as the dominant luminosity source. The images at λ <= 2.2 microns do not completely reveal the underlying nuclei, which likely remain significantly obscured, even at 3.7 microns.

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Joe Mazzarella

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