The effect of bars on the M-sigma relation: offset, scatter and residuals correlations

TL;DR

This study uses galaxy simulations to show that bar formation in disc galaxies increases bulge velocity dispersion, causing deviations from the standard M-sigma relation and increasing scatter, with implications for understanding black hole-host galaxy correlations.

Contribution

It demonstrates how bar formation affects the M-sigma relation, revealing offsets and increased scatter, and explores the dependence on galaxy components and properties.

Findings

Bar formation raises sigma by ~12-20%.

Barred galaxies show offset and increased scatter in M-sigma.

Offset correlates with bulge-to-disc mass ratio and anisotropy.

Abstract

We analyse a set of collisionless disc galaxy simulations to study the consequences of bar formation and evolution on the M-sigma relation of supermassive black holes. The redistribution of angular momentum driven by bars leads to a mass increase within the central region, raising the velocity dispersion of the bulge, sigma, on average by ~12% and as much as ~20%. If a disc galaxy with a SMBH satisfying the M-sigma relation forms a bar, and the SMBH does not grow in the process, then the increase in sigma moves the galaxy off the M-sigma relation. We explore various effects that can affect this result including contamination from the disc and anisotropy. The displacement from the M-sigma relation for individual model barred galaxies correlates with both M(B)/M(B+D) and beta_phi(B+D) measured within the effective radius of the bulge. Overall, this process leads to an M-sigma for barred galaxies offset from that of unbarred galaxies, as well as an increase in its scatter. We assemble samples of unbarred and barred galaxies with classical bulges and find tentative hints of an offset between the two consistent with the predicted. Including all barred galaxies, rather than just those with a classical bulge, leads to a significantly larger offset.