Axisymmetric mass models of S0 and spiral galaxies with boxy bulges: mass-to-light ratios, dark matter and bars

TL;DR

This study models the stellar kinematics of 30 edge-on spiral and S0 galaxies with boxy bulges using axisymmetric mass models, finding no evidence for dominant dark matter within the optical disk and supporting the bar interpretation of bulges.

Contribution

It introduces a simple axisymmetric modelling approach with a single free parameter to analyze stellar kinematics and dark matter content in edge-on galaxies with boxy bulges.

Findings

Good fit of models to observed stellar kinematics within optical extent

No evidence for dominant dark matter within the optical disk

Supports the view that boxy bulges are bars viewed edge-on

Abstract

We examine a sample of 30 edge-on spiral and S0 galaxies that have boxy and peanut-shaped bulges. We compute model stellar kinematics by solving the Jeans equations for axisymmetric mass distributions derived from K-band images. These simple models have only one free parameter: the dynamical mass-to-light ratio, which we assume is independent of radius. Given the simplicity of the modelling procedure, the model second velocity moments are strikingly good fits to the observed stellar kinematics within the extent of our kinematic data, which typically reach ~ 0.5-1 R25 (where R25 is the optical radius), or equivalently 2-3 Re (where Re is the effective or half-light radius). We therefore find no evidence for a dominant dark matter component within the optical disk of spiral galaxies. This is equally true of the S0s in our sample, which significantly extends previous observational constraints on dark matter in these galaxies. The predicted kinematics do deviate slightly but systematically from the observations in the bulge region of most galaxies, but we argue that this is consistent with the claim that boxy and peanut-shaped bulges are bars viewed edge-on.