VLT-SINFONI sub-kpc study of the star formation in local LIRGs and
  ULIRGs: Analysis of the global $\Sigma_{\rm SFR}$ structure and
  characterisation of individual star-forming clumps
  We present a 2D study of star formation at kpc and sub-kpc scales of a sample
of local (z<0.1) U/LIRGs, based on near-IR VLT-SINFONI observations. We
obtained integrated measurements of the star formation rate (SFR) and star
formation rate surface density, together with their 2D distributions, based on
Br_gamma and Pa_alpha emission. We observe a tight linear correlation between
the SFR derived from our extinction-corrected measurements and that derived
from 24 micron data, and a reasonable agreement with SFR derived from total IR
luminosity. Our near-IR measurements are on average a factor 3 larger than
optical SFR, even when extinction corrections are applied. We found that LIRGs
have a median-observed star formation rate surface density of 1.72
Msun/yr/kpc^2 for the extinction-corrected distribution, whilst ULIRGs have
0.23 Msun/yr/kpc^2, respectively. These median values for ULIRGs increase up to
2.90 Msun/yr/kpc^2, when only their inner regions, covering the same size as
the average FoV of LIRGs, are considered. We identified a total of 95
individual SF clumps in our sample, with sizes within 60-1500pc, and
extinction-corrected Pa_alpha luminosities of 10^5-10^8 Lsun. Star-forming
clumps in LIRGs are about ten times larger and thousands of times more luminous
than typical clumps in spiral galaxies. Clumps in ULIRGs have sizes similar
(x0.5-1) to those of high-z clumps, having Pa_alpha luminosities similar to
some high-z clumps, and about 10 times less luminous than the most luminous
high-z clumps identified so far. We also observed a change in the slope of the
L-r relation. A likely explanation is that most luminous galaxies are
interacting and merging, and therefore their size represents a combination of
the distribution of the star-forming clumps within each galaxy in the system
plus the effect of the projected distance.
