Starburst and old population in z=3.8 radio galaxies with Pégase.3

Abstract

Distant radio galaxies, hosted by massive ellipticals, follow the galaxy evolution process on an extremely large (0 = z =7) time-scale = 10 12Gyrs, up to primeval galaxies. The new evolutionary code Pégase.3 predicts on similar time-scales, the coupled stellar and dust emissions of various galaxy types: starbursts and Hubble sequence types. All z=0 templates are fitted on local observations at ages ?13 Gyrs (except irregulars at 9 Gyrs). The multi-? spectral energy distributions (SEDs) of two z=3.8 radiogalaxies, including the most recent Herschel data from the HeRGÉ consortium, are interpreted in the observer's frame by Rocca-Volmerange et al. (2012) with Pégase.3. The apparent SEDs are fitted at best with the sum of a young starburst and an older early-type population, an AGN simple model is taken into account. These results favor massive gas-rich mergers at work in evolved galaxies at z?4. Massive starbursts would be at the origin of galaxy evolution initiated at the earliest epochs (z for=10). The possible relation with super massive black holes is still debated. © 2013 International Astronomical Union.