The Millennium Galaxy Catalogue:
The local supermassive black hole mass function
in early- and late-type galaxies
Authors:Alister W. Graham, Simon P. Driver, Paul D. Allen, Jochen Liske
Abstract:
We provide a new estimate of the local supermassive black hole mass function
using (i) the empirical relation between supermassive black hole mass
and the Sersic index of the host spheroidal stellar system and (ii)
the measured (spheroid) Sersic indices drawn from 10k galaxies in the
Millennium Galaxy Catalogue.
The observational simplicity of our approach, and the direct measurements of
the black hole predictor quantity, i.e. the Sersic index, for both
elliptical galaxies and the bulges of disc galaxies makes it straightforward
to estimate accurate black hole masses in early- and late-type galaxies alike.
We have parameterised the supermassive black hole mass function with a
Schechter function and find, at the low-mass end, a logarithmic slope
(1+α) of ~0.7 for the full galaxy sample and ~1.0 for the
early-type galaxy sample. Considering spheroidal stellar systems brighter
than MB = -18 mag, and integrating down to black hole masses of 106
MSun, we find that the local mass density of supermassive black holes in
early-type galaxies ρbh, early-type = (3.5±1.2) x 105
h370 MSun Mpc-3, and in late-type galaxies
ρbh, late-type = (1.0±0.5) x 105
h370 MSun Mpc-3. The
uncertainties are derived from Monte Carlo simulations which include
uncertainties in the Mbh-n relation, the catalogue of Sersic
indices, the galaxy weights and Malmquist bias. The combined, cosmological,
supermassive black hole mass density is thus Ωbh, total = (3.2±1.2) x 10-6 h70. That is, using a new and independent method,
we conclude that (0.007±0.003)h703 per cent of the universe's baryons
are presently locked up in supermassive black holes at the centres of galaxies.