2009A&A...506.1541A

Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) are key cosmological classes since they account for most of the co-moving star formation rate density at z∼1-2. It is then important to have detailed studies of local samples of their counterparts for understanding the internal and dynamical processes taking place at high-z. To characterize the two-dimensional morphological, excitation and kinematic properties of LIRGs and ULIRGs we are carrying out an optical integral field spectroscopy (IFS) survey of local (z<0.26) samples. In this paper we present optical (3800-7200Å) IFS with the Potsdam multi-aperture spectrophotometer (PMAS) of the northern hemisphere portion of a volume-limited (2750-5200km/s) sample of 11 LIRGs. The PMAS IFS observations typically cover the central ∼5kpc and are complemented with our own existing HST/NICMOS images. For most LIRGs in our sample, the peaks of the continuum and gas (e.g., Hα, [NII]λ6584) emissions coincide, unlike what is observed in local, strongly interacting ULIRGs. The only exceptions are galaxies with circumnuclear rings of star formation where the most luminous Hα emitting regions are found in the rings rather than in the nuclei of the galaxies, and the displacements are well understood in terms of differences in the stellar populations. A large fraction of the nuclei of these LIRGs are classified as LINER and intermediate LINER/HII, or composite objects, which is a combination of starformation and AGN activity. The excitation conditions of the integrated emission depend on the relative contributions of HII regions and the diffuse emission to the line emission over the PMAS FoV. Galaxies dominated by high surface-brightness HII regions show integrated HII-like excitation. A few galaxies show slightly larger integrated [NII]λ6584/Hα and [SII]λ6717,6731/Hα line ratios than the nuclear ones, probably because of more contribution from the diffuse emission. The Hα velocity fields over the central few kpc are generally consistent, at least to first order, with rotational motions. The velocity fields of most LIRGs are similar to those of disk galaxies, in contrast to the highly perturbed fields of most local, strongly interacting ULIRGs. The peak of the Hα velocity dispersion coincides with the position of the nucleus and is likely to be tracing mass. All these results are similar to the properties of z∼1 LIRGs, and they highlight the importance of detailed studies of flux-limited samples of local LIRGs.