Paper detail

Is the black hole in NGC1277 really over-massive?

A claim has been made by van den Bosch et al. (2012) that NGC1277 hosts an over-massive BH with a mass larger than half its spheroid mass. We revisit this claim by examining the predictions from dynamical realisations based on new MGE models of NGC1277. We present realisations which fit the observed photometry. M/L is fixed following scaling relations which predict a Salpeter-like IMF. A model without a BH provides a surprisingly good fit of the observed kinematics outside the unresolved central region, but not, as expected, of the central dispersion and h4 values. A model with a MBH of 5 10^9 Msun allows to fit the dispersion profile, consistently with models of the same mass and M/L in vdB+12. It departs from the central h4 values by only about twice the given uncertainty. A slightly varying M/L or the addition of high velocity stars would further lower the need for a very massive BH. These results do not rule out the presence of an over-massive BH at the centre of NGC1277. However, they lead us to advocate the use of 3-sigma confidence intervals for derived MBH as better, more conservative, guidelines for such studies. We caution for the use of ill-defined spheroidal components as an input for scaling relations, and emphasise the fact that a MBH in the range 2-5 10^9 Msun would represent less than 5% of the spheroid mass of our models. This would make the BH in NGC1277 consistent or just twice as large as what a recent version of the MBH-sigma relation predicts. We examine the impact of the presence of a bar by running simulations from the same MGE model but with extreme anisotropies. An inner small bar forms, and an end-on view gets closer to fitting the central dispersion profile without the need for a central BH, while adding a black hole of 2.5 10^9 Msun, in line with the prediction from scaling relations, allows to fit the dispersion peak and h3 profiles. EDITED and ABRIDGED.