NEAR-INFRARED [FE-II] AND PA-BETA IMAGING AND SPECTROSCOPY OF ARP-220

We have imaged the ultraluminous infrared galaxy Arp 220 in light of t he near-infrared [Fe II] 1.257 mu m and Pa beta lines, and have obtain ed spectra in the J- and H-band atmospheric windows. Arp 220 is a stro ng source of [Fe II] and Pa beta emission, with luminosities of 1.3 x 10(41) and 9.2 x 10(40) ergs s(-1), respectively. The [Fe II] and Pa b eta emission are both extended over the central 2''-3'', but with diff erent morphologies. The Pa beta line is strongly peaked at the positio n of the western nucleus seen at 2.2 mu m (Graham et al. 1990) with a fainter ''spur'' in the direction of the eastern nucleus. The [Fe II] emission line shows a weak peak at the western nucleus along with diff use emission extending to the east, but with no indication of a second ary maximum. The [Fe II] is more extended in the north-south direction than the Pa beta line. Nearly 75% of the detected [Fe II] emission is spatially resolved. The overall [Fe II]-to-Pa beta line flux ratio in Arp 220 is consistent with that seen over similar spatial scales in S eyfert 2 galaxies, yet larger than what is measured in galaxies with n uclear starbursts. The [Fe II]-to-Pa beta line flux ratio is spatially variable being approximately 0.8 at the position of the western nucle us and approximately 2.0 at radii of up to 500 pc. We suggest that the extended [Fe II] emission is produced through the interaction of fast shocks with ambient gas in the ISM at the base of the outflowing, sup ernovae-driven superwind mapped by Heckman et al. (1987). The bolometr ic luminosity of the starburst required to power this wind is estimate d to be at least 2 x 10(11) L.. If the spatially unresolved [Fe II] em ission is produced via a large number of supernova remnants, the impli ed rate is similar to 0.6 yr(-1). The overall luminosity of such a sta rburst could account for a large fraction (1/2-1/3) of the Arp 220 ene rgy budget, but the large deficit of ionizing photons (as counted by t he Pa beta luminosity) requires that the starburst be rapidly declinin g and/or have a low upper mass cutoff. Alternatively, dust may effecti vely compete with the gas for ionizing photons, or much of the ionizin g radiation may escape through ''holes'' in the ISM. It is also possib le that a buried AGN produces a large fraction of the unresolved [Fe I I] and Pa beta emission. We briefly discuss these possibilities in lig ht of these new imaging and spectroscopic data.