Radio loudness of high-redshift (z≥3) quasars from the Sloan Digital Sky Survey

Using a homogenous sample of 1962 quasars with redshift 3.0≤z≲4.5 drawn from the Sloan Digital Sky Survey (SDSS), we study the relationships between radio loudness, virial black hole (BH) mass and Eddington ratio (accretion rate relative to the Eddington limit). For the radio-detected objects, we find a significant (>99.5 per cent) anticorrelation between radio loudness R parameter and BH mass, consistent with previous studies of low-redshift radio-loud quasars. The truly radio-loud quasars (R>30) are found to be confined to MBH≲1010 M⊙ within our sample. We also find that R is only weakly correlated with Eddington ratio Lbol/LEdd. Combined with previous results on the low-redshift R−Lbol/LEdd relation, this result indicates no strong Lbol/LEdd dependence of R at Lbol/LEdd≳10−2. On the other hand, the large scatter in these relationships suggests that other physical properties such as BH spin and quasar clustering must also play an important role in quasar radio emission.