Determination of the Intrinsic Scatter in the MBH-σ and MBH-Lbulge Relations

We derive improved versions of the relations between supermassive black hole mass M_BH and host-galaxy bulge velocity dispersion σ and luminosity L (the M_BH-σ and M_BH-L_bulge relations), based on ~ 50 M_BH measurements and ~ 20 upper limits. Particular attention is paid to recovery of the intrinsic scatter (ɛ₀) in both relations. We find the scatter to be significantly larger than estimated in most previous studies. The large scatter requires revision of the local black hole mass function, and it implies that there may be substantial selection bias in studies of the evolution of the M_BH-σ and M_BH-L_bulge relations. When only considering ellipticals, the scatter decreases. These results appear to be insensitive to a wide range of assumptions about the measurement errors and the distribution of intrinsic scatter. We also investigate the effects on the fits of culling the sample according to the resolution of the black hole's sphere of influence.