The Ubiquity of Supermassive Black Holes in the Hubble Sequence

TL;DR

This study demonstrates that supermassive black holes are common across all galaxy types, including bulgeless galaxies, and that their mass correlates with the total stellar mass of the host galaxy, not just the bulge.

Contribution

It provides the first large-scale evidence that supermassive black holes are present in all galaxy morphologies, challenging the previous bulge-centric correlation models.

Findings

Supermassive black holes are found in all galaxy types, including bulgeless galaxies.

The black hole mass correlates with the total stellar mass of the galaxy.

The fraction of bulgeless galaxies hosting black holes is about 9%.

Abstract

We present the results of a study of a statistically significant sample of galaxies which clearly demonstrate that supermassive black holes are generically present in all morphological types. Our analysis is based on the quantitative morphological classification of 1.12 million galaxies in the SDSS DR7 and on the detection of black hole activity via two different methods, the first one based on their X-ray/radio emission and the second one based on their mid-infrared colors. The results of the first analysis confirm the correlation between black hole and total stellar mass for 8 galaxies and includes one galaxy classified as bulgeless. The results of our second analysis, consisting of 15,991 galaxies, show that galaxies hosting a supermassive black hole follow the same morphological distribution as the general population of galaxies in the same redshift range. In particular, the fraction of bulgeless galaxies, 1,450 galaxies or 9 percent, is found to be the same as in the general population. We also present the correlation between black hole and total stellar mass for 6,247 of these galaxies. Importantly, whereas previous studies were limited to primarily bulge-dominated systems, our study confirms this relationship to all morphological types, in particular, to 530 bulgeless galaxies. Our results indicate that the true correlation that exists for supermassive black holes and their host galaxies is between the black hole mass and the total stellar mass of the galaxy and hence, we conclude that the previous assumption that the black hole mass is correlated with the bulge mass is only approximately correct.