The rotation curves of flattened Sersic bulges

TL;DR

This paper introduces a method to deproject flattened Sersic bulges to accurately derive their 3D luminosity profiles and assess their impact on galaxy rotation curves, highlighting the importance of considering bulge flattening.

Contribution

It provides a novel deprojection technique for axisymmetric bulges with arbitrary flattening and analyzes how bulge shape affects rotation curve interpretation.

Findings

Rotation curves are significantly affected by bulge flattening and concentration.

Neglecting bulge flattening can lead to 30% overestimation of mass-to-light ratio.

Proper modeling reduces errors in galaxy mass decomposition.

Abstract

I present a method to deproject the observed intensity profile of an axisymmetric bulge with arbitrary flattening to derive the 3D luminosity density profile and to calculate the contribution of the bulge to the rotation curve. I show the rotation curves for a family of fiducial bulges with Sersic surface brightness profiles and with various concentrations and intrinsic axis ratios. Both parameters have a profound impact on the shape of the rotation curve. In particular, I show how the peak rotation velocity, as well as the radius where it is reached, depend on both parameters. I also discuss the implications of the flattening of a bulge for the decomposition of a rotation curve and use the case of NGC 5533 to show the errors that result from neglecting it. For NGC 5533, neglecting the flattening of the bulge leads to an overestimate of its mass-to-light ratio by approximately 30% and an underestimate of the contributions from the stellar disc and dark matter halo in the regions outside the bulge-dominated area.