Dynamical Properties of Ultraluminous Infrared Galaxies. II. Traces of Dynamical Evolution and End Products of Local Ultraluminous Mergers

Abstract

We present results from our Very Large Telescope large program to study the dynamical evolution of local ultraluminous infrared galaxies (ULIRGs) and QSOs. This paper is the second in a series presenting the stellar kinematics of 54 ULIRGs, derived from high-resolution, long-slit H- and K-band spectroscopy. The data presented here, including observations of 17 new targets, are mainly focused on sources that have coalesced into a single nucleus. The stellar kinematics, extracted from the CO ro-vibrational band heads in our spectra, indicate that ULIRG remnants are dynamically heated systems with a mean dispersion of 161 km s^-1. The combination of kinematic, structural, and photometric properties of the remnants indicate that they mostly originate from major mergers and that they result in the formation of systems supported by random motions, i.e., elliptical galaxies. The peak of the velocity dispersion distribution and the locus of ULIRGs on the fundamental plane of early-type galaxies indicate that the end products of ultraluminous mergers are typically moderate-mass ellipticals (of stellar mass ~10¹⁰-10¹¹ M_☉). Converting the host dispersion into black hole mass with the aid of the M_BH-σ relation yields black hole mass estimates of the order 10⁷-10⁸ M_☉ and high accretion rates with Eddington efficiencies often >0.5.