  We present a NIR analysis of a sample of H2 outflows from young embedded
sources to compare the physical properties and cooling mechanisms of the
different flows. The sample comprises 23 outflows driven by Class 0 and I
sources having low-intermediate luminosity. We have obtained narrow band images
in H2 2.12um and FeII 1.64um and spectroscopic observations in the range
1-2.5um. H2 line ratios have been used to estimate the visual extinction and
average temperature of the molecular gas. Av values range from 2 to 15mag;
average temperatures range between 2000 and 4000K. In several knots a
stratification of temperatures is found with maximum values up to 5000K. Such a
stratification is more commonly observed in those knots which also show FeII
emission, while a thermalized gas at a single temperature is generally found in
knots emitting only in molecular lines. Combining narrow band imaging with the
parameters derived from the spectral analysis, we are able to measure the total
luminosity of the H2 and FeII shocked regions in each flow. H2 is the major IR
coolant with an average L(H2)/L(FeII) ratio of 10^{-2}. 83% of the sources have
a L(H2)/L(bol) ratio of 0.04, irrespective of the Class of the driving source,
while a smaller group of sources have L(H2)/L(bol) an order of magnitude
smaller.Such a separation reveals the non-homogeneous behaviour of ClassI,
where sources with very different outflow activity can be found. This is
consistent with other studies showing that among ClassI one can find objects
with different accretion properties and it demonstrates that the H2 power in
the jet can be a powerful tool to identify the most active sources of this
class.
