The Star Formation History of Redshift z~2 Galaxies: The Role of The
  Infrared Prior
  We build a sample of 298 spectroscopically-confirmed galaxies at redshift
z~2, selected in the z-band from the GOODS-MUSIC catalog. By exploiting the
rest frame 8 um luminosity as a proxy of the star formation rate (SFR) we check
the accuracy of the standard SED-fitting technique, finding it is not accurate
enough to provide reliable estimates of the galaxy physical parameters. We then
develop a new SED-fitting method that includes the IR luminosity as a prior and
a generalized Calzetti law with a variable RV . Then we exploit such a new
method to re-analyze our galaxy sample, and to robustly determine SFRs, stellar
masses and ages. We find that there is a general trend of increasing
attenuation with the SFR. Moreover, we find that the SFRs range between a few
to 1000 solar mass per year, the masses from one billion to 400 billion solar
masses, while the ages from a few tens of Myr to more than 1 Gyr. We discuss
how individual age easurements of highly attenuated objects indicate that dust
must form within a few tens of Myr and be copious already at ~100 Myr. In
addition, we find that low luminous galaxies harbor, on average, significantly
older stellar populations and are also less massive than brighter ones; we
discuss how these findings and the well known 'downsizing' scenario are
consistent in a framework where less massive galaxies form first, but their
star formation lasts longer. Finally, we find that the near-IR attenuation is
not scarce for luminous objects, contrary to what is customarily assumed; we
discuss how this affects the interpretation of the observed mass-to-light
ratios.
