CEA, Saclay, France
We will review ISOCAM mid-infrared extragalactic surveys aimed at
unveiling dust enshrouded star formation in the universe. Several
regions of the sky, clean of foreground infrared emission, were
observed in the 6.75 and 15 microns ISOCAM broadband filters, ranging
from large and shallow to narrower and deeper surveys. The total flux
range covers about three orders of magnitude from 100 
to about
0.1 Jy.
The counts obtained above 1 mJy by various surveys in the 12-18 micron
band are in good agreement with the no-evolution model. On the
contrary, strong evolution is observed in the counts below 1 mJy by
deeper surveys. This evolution seems to be due to a population of
star-forming or post starburst galaxies typically below
,
whose
optical properties are not very different from the galaxies in the
field and hence would not have been selected by optical surveys. The
steep rise of the number counts indicates that more star formation is
hidden in the infrared at larger redshifts with respect to optical-UV
emission.