SIMBAD references

The question as to whether the distribution of radio loudness in active galactic nuclei (AGNs) is actually bimodal has been discussed extensively in the literature. Furthermore, there have been claims that radio loudness depends on black hole mass (M_BH) and Eddington ratio (L_bol/L_Edd). We investigate these claims using the low-redshift broad line AGN sample of Greene & Ho, which consists of 8434 objects at z < 0.35 from the Sloan Digital Sky Survey Fourth Data Release (SDSS DR4). We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGNs, 821 have corresponding observed radio fluxes in the FIRST survey. We calculated the radio-loudness parameter () for all objects above the FIRST detection limit (1 mJy), and an upper limit to for the undetected objects. Using these data, the question of radio bimodality is investigated for different subsets of the total sample. We find no clear demarcation between the radio loud (RL; > 10) and radio quiet ( < 10) objects, but instead fill in a more radio-intermediate population in a continuous fashion for all subsamples. We find that 4.7% of the AGNs in the flux-limited subsample are RL based on core radio emission alone. We calculate the radio-loud fraction (RLF) as both a function of M_BHand L_bol/L_Edd. The RLF decreases (from 13% to 2%) as L_bol/L_Eddincreases over 2.5 orders of magnitude. The RLF is nearly constant (∼5%) over four decades in M_BH, except for an increase at M_BH> 10⁸ M_☉. We find for the FIRST detected subsample that 367 of the RL AGNs have M_BH < 10⁸ M_☉, a large enough number to indicate that RL AGNs are not a product of only the most massive black holes in the local universe.