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 the near-infrared (Fe II) 1.257 micron and Pa-beta lines, and have obtained spectra in the J- and H-band atmospheric windows. Arp 220 is a strong source of (Fe II) and Pa-beta emission, with luminosities of 1.3 x 10(exp 41) and 9.2 x 10(exp 40) ergs/s, respectively. The (Fe II) and Pa-beta emission are both extended over the central 2 sec-3 sec, but with different morphologies. We suggest that the extended (Fe II) emission is produced through the interaction of fast shocks with ambient gas in the interstellar medium (ISM) at the base of the outflowing, supernovae-driven superwind mapped by Heckman et al. (1987). The bolometric luminosity of the starburst required to power this wind is estimated to be at least 2 x 10(exp 11) solar luminosity. If the spatially unresolved (Fe II) emission is produced via a large number of supernova remnants, the implied rate is approximately 0.6/yr. The overall luminosity of such a starburst could account for a large fraction (1/2-1/3) of the Arp 220 energy budget, but the large deficit of ionizing photons (as counted by the Pa-beta luminosity) requires that the starburst be rapidly declining and/or have a low upper mass cutoff. Alternatively, dust may effectively compete with the gas for ionizing photons, or much of the ionizing radiation may escape through 'holes' in the ISM. It is also possible that a buried active galactic nuclei (AGN) produces a large fraction of the unresolved (Fe II) and Pa-beta emission. We briefly discuss these possibilities in light of these new imaging and spectroscopic data.