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Centro de Astrofísica da Universidade do Porto

The VVDS-VLA deep field - IV. Radio-optical properties

S. Bardelli, E. Zucca, M. Bolzonella, P. Ciliegi, L. Gregorini, G. Zamorani, M. Bondi, A. Zanichelli, L. Tresse, D. Vergani, I. Gavignaud, A. Bongiorno, D. Bottini, B. Garilli, V. Le Brun, O. Le Fèvre, D. Maccagni, R. Scaramella, M. Scodeggio, G. Vettolani, C. Adami, S. Arnouts, A. Cappi, S. Charlot, T. Contini, S. Foucaud, P. Franzetti, L. Guzzo, O. Ilbert, A. Iovino, F. Lamareille, H. J. McCracken, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, R. Pellò, A. Pollo, L. Pozzetti, M. Radovich, U. Abbas, J. Brinchmann, O. Cucciati, S. de la Torre, L. de Ravel, P. Memeo, E. Pérez-Montero, Y. Mellier, P. Merluzzi, S. Temporin, H. R. De Ruiter, P. Parma

Aims. The availability of wide angle and deep surveys, both in the optical and the radio band, allows us to explore the evolution of radio sources with optical counterparts up to redshift z ∼ 1.1 in an unbiased way using large numbers of radio sources and well defined control samples of radio-quiet objects.
Methods. We use the 1.4 GHz VIMOS-VLA Deep Survey, the optical VIMOS-VLT Deep Survey and the CFHT Legacy Survey to compare the properties of radio-loud galaxies with respect to the whole population of optical galaxies. The availability of multiband photometry and high quality photometric redshifts allows us to derive rest-frame colors and radio luminosity functions to a limit of a B rest-frame magnitude of MB = −20. We derive spectrophotometric types, following the classification of Zucca et al. (2006, A&A, 455, 879), in order to have a priori knowledge of the optical evolution of different galaxy classes.
Results. Galaxy properties and luminosity functions are estimated up to z ∼ 1 for radio-loud and radio-quiet early and late type galaxies. Radioloud late type galaxies show significantly redder colors than radio-quiet objects of the same class and this is related to the presence  of more dust in stronger star forming galaxies. We estimate the optical luminosity functions, stellar masses and star formation rate distributions for radio sources and compare them with those derived for a well defined control sample, finding that the probability of a galaxy to be a radio emitter significantly increases at high values of these parameters. Radio-loud early type galaxies exhibit luminosity evolution in their bivariate radio-optical luminosity function, due to evolution in the radio-optical ratio. The lack of evolution of the mass function of radio-loud early type galaxies means that no new AGN are formed at redshift z < 1. In contrast, radio-loud late type objects exhibit a strong evolution, both in luminosity and density, of the radio luminosity function for z > 0.7. This evolution is a direct effect of the strong optical evolution of this class and no significant change with redshift in the radio-optical ratio is required. With the knowledge of the radio-optical ratio and the optical and radio luminosity functions for late type galaxies, we show that it is possible to estimate the star formation history of the Universe up to redshift z ∼ 1.5, using optical galaxies as tracers of the global radio emission.

Astronomy and Astrophysics
Volume 495, Page 431
February 2009

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