The Spiral Pattern Speed in the Milky Way Galaxy

TL;DR

This study estimates the spiral pattern speed in the Milky Way using maser kinematics, revealing two possible values depending on the sign correlation of velocity components, with implications for galactic dynamics.

Contribution

The paper introduces a spectral analysis method to determine the spiral pattern speed and related parameters using maser data, accounting for velocity perturbations and sign variations.

Findings

Estimated pattern speeds of 25.8 and 35.4 km/s/kpc.

Confirmed periodic vertical velocity perturbations in masers.

Identified the dependence of pattern speed on velocity component signs.

Abstract

For a sample of masers, the basic kinematic equations were solved by including the Galactic rotation parameters and the peculiar velocity of the Sun as the unknown variables. Based on spectral analysis, the following estimates were obtained: $|f|_{R,\theta}=(7.0,5.1)\pm(1.2,1.4)$ km s$^{-1}$ and the corresponding wavelengths $\lambda_{R,\theta}=(1.9,1.7)\pm(0.4,0.7)$ kpc, as well as $\chi_\odot=-140^\circ\pm15^\circ$. The presence of periodic perturbations in the vertical velocities of masers with an amplitude of $|f|_W=3.1\pm1.4$ km s$^{-1}$ and a wavelength of $\lambda=1.9\pm0.8$ kpc was confirmed. It is shown that the velocities $f_R$ and $f_\theta$ can have both the same and different signs. Therefore, we obtained a large scatter of estimates. Thus, if $f_R$ and $f_\theta$ have the same signs, then $\Omega_p=25.8\pm2.0$ km s$^{-1}$ kpc$^{-1}$ and $R_{cor}=9.1\pm0.8$ kpc. And when $f_R$ and $f_\theta$ have different signs, then $\Omega_p=35.4\pm2.0$ km s$^{-1}$ kpc$^{-1}$ and $R_{cor}=6.8\pm0.8$ kpc.