Radiogalaxies in the Sloan Digital Sky Survey: spectral index-environment correlations

BORNANCINI, C. G.; O'MILL, A. L.; GARCÍA LAMBAS, D.; GUROVICH, S.

Boletin de la Asociación Argentina de Astronomía

Asociación Argentina de Astronomía

Lugar: Buenos Aires; Año: 2009 vol. 52 p. 165 - 168

1669-9521

We analyze optical and radio properties of radiogalaxies detected in the Sloan Digital Sky Survey (SDSS). The sample of radio sources was selected from the catalogue of Kimball & Ivezic (2008). We construct a Hubble dia- gram of Ultra Steep spectrum (USS, alpha<-1, where S_nu ~ nu(alpha) ) radio sources in the optical r band and compare our results with those for normal galaxies and find that USS radio sources are about as luminous as the central galax- ies in the maxBCG cluster sample and typically more than 4 magnitudes brighter than normal galaxies at z˜0.3. We also study correlations between the spectral index, richness and luminosity of clusters associated with radio sources. Our results suggest that clusters of galaxies associated with steeper than average spectra have higher richness counts and are populated by lu- minous galaxies in comparison with those environments associated to radio sources with flatter than average spectra.