VLT-SINFONI integral field spectroscopy of low-z luminous and
  ultraluminous infrared galaxies I. Atlas of the 2D gas structure
  We present an atlas of a sample of local (U)LIRGs covering the luminosity
range log(L_IR/L_sun)=11.1-12.4. The atlas is based on near-infrared H and
K-band VLT-SINFONI IFS, and presents the ionised, partially ionised, and warm
molecular gas 2D flux distributions and kinematics over a FoV of 3x3 kpc
(LIRGs) and 12x12kpc (ULIRGs) and with average linear resolutions of 0.2kpc and
0.9kpc, respectively. The different phases of the gas show a wide morphological
variety with the nucleus as the brightest Br_g source for 33% of the LIRGs and
71% of the ULIRGs, whereas all the (U)LIRGs have their maximum H_2 emission in
their nuclear regions. In LIRGs, the ionised gas distribution is dominated by
the emission from the star-forming rings or giant HII regions in the spiral
arms. The Br_g and [FeII] line at 1.644 micron trace the same structures,
although the emission peaks at different locations in some of the objects, and
the [FeII] seems to be more extended and diffuse. The ULIRG subsample contains
mainly pre-coalescence interacting systems. Although the peaks of the molecular
gas emission and the continuum coincide in 71% of the ULIRGs, regions with
intense Pa_a (Br_g) emission tracing luminous star-forming regions located at
distances of 2-4kpc away from the nucleus are also detected, usually associated
with secondary nuclei or tidal tails. The gas kinematics in LIRGs are primarily
due to rotational motions around the centre of the galaxy, although local
deviations associated with radial flows and/or regions of higher velocity
dispersions are present. The ionised and molecular gas share the same
kinematics to first order, showing slight differences in the velocity
amplitudes in some cases, whereas the average velocity dispersions are
compatible within uncertainties. As expected, the kinematics of the ULIRG
subsample is more complex, owing to the interacting nature of the objects of
the sample.
