2006PASJ...58..813I

We present ground-based infrared K-(2-2.5µm) and L-band (2.8-4.1µm) spectroscopy, as well as interferometric observations at l∼3mm, for the individual merging components (A, B, and C) of the luminous infrared galaxy Arp 299. The presence and location of a buried active galactic nucleus (AGN) are investigated. Our sub-arcsec-resolution infrared spectra clearly reveal that the putative buried AGN resides in the nucleus B1 (a subcomponent of B), based on a very low equivalent width of 3.3µm polycyclic aromatic hydrocarbon emission, a weak 2.3µm CO absorption feature, and a large time variation of the K- and L-band continuum fluxes. Our interferometric observations simultaneously obtain HCN (J = 1-0) and HCO⁺ (J = 1-0) emission lines with ∼ 4'' resolution, and we find the HCN to HCO⁺ brightness-temperature ratios to be as low as those found in starburst nuclei in all of the major merging components of Arp 299. The low ratio even in the AGN-hosting nucleus B may be due to the presence of a large amount of high-density molecular gas whose chemistry is dominated by coexisting starbursts and/or shocks, rather than by the central strong X-ray-emitting AGN.