VLT-SINFONI integral field spectroscopy of low-z luminous and
  ultraluminous infrared galaxies II. 2D extinction structure and distance
  effects
  We present a 2D study of the internal extinction on (sub)kiloparsec scales of
a sample of local (z<0.1) (U)LIRGs, based on near-infrared Pa_a, Br_d, and Br_g
line ratios, obtained with VLT-SINFONI integral-field spectroscopy. The 2D
extinction (Av) distributions of the objects, map regions of ~3x3 kpc (LIRGs)
and ~12x12 kpc (ULIRGs), with average angular resolutions (FWHM) of ~0.2 kpc
and ~0.9 kpc, respectively. The individual Av galaxy distributions indicate a
very clumpy dust structure already on sub-kiloparsec scales, with values (per
spaxel) ranging from Av ~ 1 to 20 mag in LIRGs, and from Av ~ 2 to 15 mag in
ULIRGs. As a class, the median values of the distributions are Av=5.3 mag and
Av=6.5 mag for the LIRG and ULIRG subsamples, respectively.
  We evaluated the effects of the galaxy distance in the measurements of the
extinction as a function of the linear scale (in kpc) of the spaxel (i.e. due
to the limited angular resolution of the observations). If the distribution of
the gas/dust and star-forming regions in local LIRGs (63 Mpc, 40 pc/spaxel on
average) is the same for galaxies at greater distances, the observed median Av
values based on emission line ratios would be a factor ~0.8 lower at the
average distance of our ULIRG sample (328 Mpc, 0.2 kpc/spaxel), and a factor
~0.67 for galaxies located at distances of more than 800 Mpc (0.4 kpc/spaxel).
This distance effect would have implications for deriving the intrinsic
extinction in high-z star-forming galaxies and for subsequent properties such
as star formation rate, star formation surface density, and KS- law, based on
H_alpha line fluxes. If local LIRGs are analogues of the main-sequence
star-forming galaxies at cosmological distances, the extinction values (Av)
derived from the observed emission lines in these high-z sources would need to
be increased by a factor 1.4 on average.
