Black-hole mass estimates for a homogeneous sample of bright
  flat-spectrum radio quasars
  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.
