# Estimating the baryonic masses of face-on spiral galaxies from stellar kinematics

## TL;DR

This paper refines methods to estimate baryonic masses in face-on spiral galaxies using stellar kinematics, accounting for dark matter halos and disc structure, revealing that true stellar mass-to-light ratios decrease with radius.

## Contribution

It introduces a more realistic model for vertical gravity correction, showing that stellar mass-to-light ratios vary with radius and that dark matter halo effects are significant.

## Key findings

- Vertical gravity corrections increase derived stellar surface densities.
- True mass-to-light ratios decrease with radius, matching photometric gradients.
- Gaseous disc effects and thick-disc components significantly influence mass estimates.

## Abstract

The kinematic dispersions of disc stars can be used to measure the dynamic contributions of baryons to the rotation curves of spiral galaxies and hence to trace the amount and distribution of the remaining dark matter. However, the simple single-component infinite disc model traditionally used to convert stellar dispersions to mass-densities is no longer adequate. The dark matter halo has a significant effect upon the stellar dispersions for any non-maximal disc. The correction for cuspy dark matter halos is particularly large, suggesting that such models are not consistent with the observed stellar dispersions. When a more realistic model for the vertical gravity of the disc is used, the derived stellar surface densities are generally larger (smaller) for disc radii smaller (larger) than 2.3 times the radial scale-length. When the vertical gravity correction is applied to the radially resolved stellar mass-to-light ratios derived by the DiskMass consortium, the true values are not constant but decrease with radius, as expected from photometric colour gradients, and the true mass scale-lengths are about 80% of the photometric scale-lengths. The effects of a thin gaseous disc are larger than expected, especially when an allowance is made for optically thick or CO-dark gas. The presence of a thick-disc stellar component has severe consequences, particularly if its radial scale-length is smaller than that of the thin disc, as it appears to be in the Milky Way.