Spiral and bar driven peculiar velocities in Milky Way sized galaxy simulations

TL;DR

This study compares different galaxy simulation models to observed stellar velocities, finding that models with a bar and transient spiral arms best match real data, and highlights the power spectrum as a key diagnostic tool.

Contribution

It introduces a method using power spectrum analysis of velocity fields to distinguish between spiral galaxy models, validated with Milky Way-sized galaxy simulations.

Findings

Power spectrum matches APOGEE data for bar and transient spiral models.

Sensitivity of power spectrum to spiral arm properties like pitch angle.

Line of sight velocities alone are insufficient to distinguish models.

Abstract

We investigate the kinematic signatures induced by spiral and bar structure in a set of simulations of Milky Way-sized spiral disc galaxies. The set includes test particle simulations that follow a quasi-stationary density wave-like scenario with rigidly rotating spiral arms, and $N$-body simulations that host a bar and transient, co-rotating spiral arms. From a location similar to that of the Sun, we calculate the radial, tangential and line-of-sight peculiar velocity fields of a patch of the disc and quantify the fluctuations by computing the power spectrum from a two-dimensional Fourier transform. We find that the peculiar velocity power spectrum of the simulation with a bar and transient, co-rotating spiral arms fits very well to that of APOGEE red clump star data, while the quasi-stationary density wave spiral model without a bar does not. We determine that the power spectrum is sensitive to the number of spiral arms, spiral arm pitch angle and position with respect to the spiral arm. However, it is necessary to go beyond the line of sight velocity field in order to distinguish fully between the various spiral models with this method. We compute the power spectrum for different regions of the spiral discs, and discuss the application of this analysis technique to external galaxies.