Vertical gradients of azimuthal velocity in a global thin disk model of spiral galaxies NGC 2403, NGC 4559, NGC 4302 and NGC 5775

TL;DR

This study estimates the vertical gradient of rotational velocity in spiral galaxies using a thin-disc model, showing the gradient's potential to reveal mass distribution and matching observed values across different galaxies.

Contribution

It demonstrates that the vertical velocity gradient can be modeled with simple rotation curves and highlights the impact of mass distribution assumptions on gradient predictions.

Findings

Gradients vary broadly and match observations.

Mass models with spheroidal components reduce predicted gradients.

Gradient behavior can inform on galaxy mass distribution.

Abstract

We estimate the vertical gradient of rotational velocity for several spiral galaxies in the framework of a global thin-disc model, using the approximation of quasi-circular orbits. We obtain gradients having a broad range of values, in agreement with measurements, for galaxies with both low and high gradients. To model the gradient, it suffices to know the rotation curve only. We illustrate, using the example of galaxy NGC 4302 with particularly high gradients, that mass models of galactic rotation curves that assume a significant spheroidal mass component reduce the predicted gradient value, which may suggest that the mass distribution is dominated by a flattened disc-like component. We conclude that the value and behaviour of the vertical gradient in rotational velocity can be used to study the mass distribution in spiral galaxies.