The Core and Extended Spectral Indices of Extragalatic Radio Sources

The relativistic beaming model has been successfully used to explain the observational properties of active galactic nuclei (AGNs).In this model the emissions are composed of two components, namely, the boosted and the isotropic extended ones.Most blazars show flat radio spectral indices, but spectral indices for core and extended components are not very clear.In this paper, we have used the observed core and total flux densities at 6 cm and 20 cm to determine the core and extended spectral indices for galaxies and QSOs, respectively.On average, the core and extended spectral indices are α_core=1.03±0.11, α_ext=0.90±0.13 for galaxies; α_core=0.29±0.09, α_ext=0.68±0.07 for QSOs. We also found :1)the core spectral index and core dominance parameter (R)show a relation:ν_c^α ∝(1+1/ R_ν);2)R is approximately linearly correlated with redshift(z).