Do black hole masses scale with classical bulge luminosities only? The case of the two composite pseudobulge galaxies NGC3368 and NGC3489

TL;DR

This study measures supermassive black hole masses in two galaxies with pseudobulges, finding that black hole scaling relations align better with classical bulge components than total bulge luminosity.

Contribution

It provides detailed SMBH mass measurements in galaxies with pseudobulges, highlighting the importance of classical bulge components in scaling relations.

Findings

SMBH masses are consistent with the M_BH-sigma relation.

Black hole masses align better with classical bulge luminosity than total bulge luminosity.

Stellar population aging may influence bulge-black hole scaling conclusions.

Abstract

It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge mass and the velocity dispersion, which implies that the bulge and the SMBH of a galaxy have grown together during the formation process. The spiral galaxy NGC3368 and the S0 galaxy NGC3489 both host a pseudobulge and a much smaller classical bulge component at the centre. We present high resolution, near-infrared IFU data of these two galaxies, taken with SINFONI at the VLT, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC3368 is M_BH=7.5x10^6 M_sun with an error of 1.5x10^6 M_sun, which mostly comes from the non-axisymmetry in the data. For NGC3489, a solution without black hole cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M_BH=6.00^{+0.56}_{-0.54} (stat) +/- 0.64 (sys) x 10^6 M_sun. Although both galaxies seem to be consistent with the M_BH-sigma relation, at face value they do not agree with the relation between bulge magnitude and black hole mass when the total bulge magnitude (i.e., including both classical bulge and pseudobulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion.