Stellar populations in radio galaxies

Abstract

We characterize the stellar population of a complete sample of the closest southern radio-galaxies – 12 Fanaroff-Riley I (FR I), 8 FR II and 4 with undefined FRx type – and a comparison sample of 18 non-active elliptical and SO galaxies. We measured equivalent widths and continuum colours and their radial variations, and performed spectral synthesis as a function of distance from the nucleus. Only 4 of the radio-galaxies have more than 10% of the total flux at 4020Å contributed from 100 Myr old or younger stellar population components – including a featureless continuum due to an AGN. All 4 are FRII or FRx. The main difference between the stellar population of the radio-galaxies and that of the non-active ones is that the former have a larger contribution of the intermediate age component, suggesting a relation between the present radio activity and a past episode of star formation which occurred about 1 Gyr ago.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html