Ratan-600–vla–BTA-6m (‘big trio’) project: Multicolor study of distant frii radio galaxies

Abstract

Abstract Powerful radio galaxies belong to the population of massive stellar systems that can be picked at high redshifts. With a measured redshift, morphology and age determination these objects can help greatly in understanding the way in which formation and evolution of giant elliptical galaxies with massive Black Holes occurred in the Early Universe. We presents some recent results of a study of the sample of 105 faint steep spectrum radio sources from RATAN-600 RC catalog. All the objects have been mapped with the VLA and optical identification has been carried out with the 6 m BTA telescope. Using multicolor CCD photometry in B, V, R c, I c bands the photometric redshift and the age of the stellar population are estimated for a subsample of 50 FRII and CSS radio galaxies. RC J0105+0501 is a very probable candidate for a radio galaxy at z ≈ 3.5. The distribution of objects on colour–colour and magnitude–redshift diagrams shows a rough agreement with expectations of theoretical models of SED evolution for giant elliptical galaxies. On the [m R – z phot] diagram two populations of faint (m R = 22m – 24m) radio galaxies are possibly revealed. The first population at z ≈ 1 consists of mainly old (a half with age ≥ 5 Gyr) and large (LAS ≈ 20″) objects, the second one at z = 1.5–3.5 includes both younger (≤ 3 Gyr) and smaller (LAS ∼ 5″) objects. There are 12 more faint or still undetected (m R ≥ 24m5) sources in the sample which can presumably be very distant radio galaxies (z > 3.5) or intermediate redshift old or dusty ones.