1999ApJ...527..778S

We have obtained images of the molecular hydrogen (H₂) and Brγ emission lines in the interacting galaxy system Arp 299. In order to investigate the nuclear activities, we also have obtained H- and K-band spectra for three of its 2 µm continuum peaks and also J-band spectra for one of them. From the line ratios of Paγ, Paβ, Br10, and Brγ, and also those between [Fe II] 1.26 µm and [Fe II] 1.64 µm, we have successfully modeled the extinction for component A as a combination of A_K=2.6 mag region(s) and A_K=0.3 mag region(s). The extinction corrected Brγ luminosity requires 5x10⁵⁴ s^–1 of Lyman photons, which corresponds to 3x10⁵ ``O6 stars.'' The mean stellar density within its 100 pc core is comparable to those for the cores in blue compact dwarf galaxies even though the luminosity is almost 2 orders of magnitude larger. The starbursts at the nucleus of component A are probably the most dominant source for the far-infrared emission from this component. In this component, we have found large [Fe II]/H I ratios, which are at the higher end of starburst galaxies and are typical for AGNs or AGN/starburst composites. The nucleus must be in a starburst phase that includes many supernova remnants. The spatial distribution of the H₂ emission for this interacting system is similar to that of the ¹²CO 1-0 emission mapped by Aalto et al. The H₂ intensity, however, is not proportional to the CO intensity among components, because of the difference in the H₂ excitation mechanism among them. We report the first possible detection of J-band H₂ lines in infrared luminous galaxies in component A, which suggests a significant contribution of nonthermal excitation mechanisms.