A multi-wavelength approach to the properties of Extremely Red Galaxy
  populations: I - Contribution to the Star Formation Rate density and AGN
  content
  We present a multi-wavelength analysis of the properties of Extremely Red
Galaxy (ERG) populations, selected in the GOODS-South/Chandra Deep Field South
field. By using all the photometric and spectroscopic information available on
large deep samples of EROs (645 sources), IEROs (294 sources), and DRGs (350
sources), we derive redshift distributions, identify AGN powered and
Star-formation powered galaxies, and, using the radio observations of this
field, estimate robust (AGN- and dust-unbiased) Star Formation Rate Densities
(SFRD) for these populations. We also investigate the properties of "pure"
(galaxies that conform to only one of the three ERG criteria considered) and
"combined" (galaxies that verify all three criteria) sub-populations. Overall,
a large number of AGN are identified (up to ~30%, based on X-rays, and
mid-infrared criteria), the majority of which are type-2 (obscured) objects.
Among ERGs with no evidence for AGN activity, we identify sub-populations
covering a wide range of average star-formation rates, from below 10 Mo/yr to
as high as 200 Mo/yr. Applying a redshift separation (1<z<2 and 2<z<3) we find
significant evolution (an increase of a factor of 2 or higher) of SFRD for EROs
and DRGs, while none is observed for IEROs. The former populations can
contribute more than 20\% to the global SFRD at 2<z<3. The emission from AGN
activity is typically not strong in the ERG population, with AGN increasing the
average radio luminosity of ERG sub-populations by, nominally, less than 20%.
AGN are common, however, and, if no discrimination is attempted, this could
significantly increase the SFRD estimate (by over 100% in some cases). Thus,
and while the contribution of star forming processes to the radio luminosity in
galaxies with AGN remains uncertain, a comprehensive identification of AGN in
these populations is necessary to obtain meaningful results.
