Abstract:
Abstract:A multi-wavelength approach to the properties of Extremely Red Galaxy populations: contribution to the Star Formation Rate density, AGN content, dust content and morphology. In this colloquium I will cover our contribution to the study of Extremely Red Galaxy (ERG) populations presenting a multi-wavelength analysis of these objects, selected in the GOODS-South/Chandra Deep Field South. By using all the photometric and spectroscopic information available on large deep samples of Extremely Red Objects (EROs, 650 sources), IRAC Extremely Red Objects (IEROs, 301 sources) and Distant Red Galaxies (DRGs, 357 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. Applying a redshift separation (1<=z<2 and 2<=z<=3) we find a significant rise (a factor of 2 or higher) of SFRD for EROs and DRGs toward high-z, while none is observed for IEROs. As expected, we find a significant overlap between the Extremely Red Galaxy populations, and investigate the properties of ``pure'' (galaxies that conform to only one of the three ERG criteria considered) and ``combined'' (galaxies conform to all three criteria) sub-populations. We find ERG sub-populations with no AGN activity and intense star-formation rates. With average values of ~200 Mo yr-1 at 2 < z <3, they reasonably contribute to the global star-formation rate density, reaching a 20% level. Strong AGN behaviour is not observed in the ERG population, with AGN onlyincreasing the average radio luminosity of ERGs by ~10%. However, AGN are frequently found, and would increase the SFRD estimate by over 100%. Thus,and while the contribution of SF 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. The dust content to each population is also derived by correlating UV and Radio SFRs, giving a higher obscuration for more active SF sources. Finally, preliminary results are presented on the morphologies of ERGs (CAS and Gini/M20 parameters) based on the v1.9 ACS GOODS-S images.