Abstract

I will discuss results from NIR spectroscopic/imaging programs that aim to determine the dynamical triggers and the time evolution of ULIR Gs. For the local sample, I will present a stellar kinematical analysis performed using the long-slit spectrograph ISAAC mounted on the VLT . The low moments of the stellar velocity profiles, extracted from the CO bandheads, indicate that local ULIR Gs are typically triggered by mergers of equal-mass, sub-m*, gas-rich galaxies and lead to the formation of moderate-mass ellipticals. The position of ULIRG remnants on the fundamental plane of early-type galaxies is well constrained in comparison with that of remnants of other interaction/merger categories (e.g. LIR Gs) and that they are less massive than local Palomar-Green (PG) QSOs. This result implies that only a subsample of the local ULIR Gs and PG QS Os can be part of the same evolutionary sequence. At redshifts 2, NICMOS2 images of 24-micron selected ULIR Gs show small fraction of perturbations in contrast to both z=2 submm galaxies and local ULIR Gs. This could be attributed to different properties in the stellar/ISM distribution between the two populations or selection effects. A bulge/disk decomposition of the brightest sources indicates that if bulges are indeed present, they are small. Therefore, at least a non-negligible number of z~2 ULIR Gs dynamically differs from their local analogues.