Radio-Loud and Radio-Quiet Quasars from the SDSS Database

Using a sample of similar to 3000 radio loud quasars (RLQs) included in the Sloan Digital Sky Survey, with 0.35 less than or similar to z less than or similar to 2.25, we study the dependence on the redshift of the black hole (BH) mass, through the application of an analysis scheme which overcomes the problems related to the Malmquist bias. Comparing the results with those from a sample dominated by radio quiet quasars (RQQs), we find that RLQs are on average more massive than RQQs and suggest that the difference fades out at z approximate to 3. We relate the BH mass gap to the observed different colors of the continuum in RLQs and RQQs and propose a picture of interpretation in terms of distinct accretion disc temperatures in the two population of quasars. Another possible explanation of the observed differentiation in the BH mass z-dependence of RLQs and RQQs is that it is clue to the effects of radiation pressure: RLQs are proposed to have a lower column density in the broad line region with respect to RQQs.