The rotation of classical bulges in barred galaxies in the presence of gas

TL;DR

This study uses hydrodynamical simulations to investigate how varying gas fractions influence the rotation and shape of classical bulges in barred galaxies, revealing that higher gas content reduces bulge rotation and affects bar strength.

Contribution

It provides new insights into the role of gas in modulating classical bulge rotation and morphology in barred galaxies through comprehensive simulations.

Findings

Higher gas fractions inhibit strong bar formation.

Bulges gain less rotation with increased gas content.

Low-mass bulges are most affected by gas fraction variations.

Abstract

Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We carried out a comprehensive set of hydrodynamical N-body simulations with different combinations of bulge masses and gas fractions. In these models, both massive bulges and high gas content tend to inhibit the formation of strong bars. For low-mass bulges, the resulting bar is stronger in cases of low gas content. In the stronger bar models, bulges acquire more angular momentum and thus display considerable rotational velocity. Such bulges also develop anisotropic velocity dispersions and become triaxial in shape. We found that the rotation of the bulge becomes less pronounced as the gas fraction is increased from 0 to 30%. These results indicate that the gas content has a significant effect on the dynamics of the classical bulge, because it influences bar strength. Particularly in the case of the low-mass bulges (10% bulge mass fraction), all of the measured rotational and structural properties of the classical bulge depend strongly and systematically on the gas content of the galaxy.