We have selected a complete sample of flat-spectrum radio quasars ( FSRQs ) from the WMAP 7-yr catalog within the SDSS area , all with measured redshift , and have compared the black hole mass estimates based on fitting a standard accretion disk model to the ‘ blue bump ’ with those obtained from the commonly used single epoch virial method .
The sample comprises 79 objects with a flux density limit of 1 Jy at 23 GHz , 54 of which ( 68 % ) have a clearly detected ‘ blue bump ’ .
Thirty-four of the latter have , in the literature , black hole mass estimates obtained with the virial method .
The mass estimates obtained from the two methods are well correlated .
If the calibration factor of the virial relation is set to f = 4.5 , well within the range of recent estimates , the mean logarithmic ratio of the two mass estimates is equal to zero with a dispersion close to the estimated uncertainty of the virial method .
The fact that the two independent methods agree so closely in spite of the potentially large uncertainties associated with each lends strong support to both of them .
The distribution of black-hole masses for the 54 FSRQs in our sample with a well detected blue bump has a median value of 7.4 \times 10 ^ { 8 } M _ { \odot } .
It declines at the low mass end , consistent with other indications that radio loud AGNs are generally associated with the most massive black holes , although the decline may be , at least partly , due to the source selection .
The distribution drops above \log ( M _ { \bullet } / M _ { \odot } ) = 9.4 , implying that ultra-massive black holes associated with FSRQs must be rare .