Detection of periodic variations in vertical velocities of Galactic masers

TL;DR

This study analyzes VLBI data of Galactic masers to detect and characterize periodic variations in their velocities, revealing spiral density wave parameters and a new vertical velocity wave with specific wavelength and amplitude.

Contribution

It provides the first detection and detailed characterization of a vertical velocity wave in Galactic masers, expanding understanding of Galactic dynamics.

Findings

Detected spiral density wave with specific amplitudes and wavelengths.

Identified a vertical velocity wave with wavelength 3.4 kpc and amplitude 4.3 km/s.

Refined parameters of the Galactic spiral structure.

Abstract

We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI. We have obtained series of residual tangential, \Delta V_{circ}, and radial, \Delta V_R, velocities for 107 masers. Based on these series, we have re-determined parameters of the Galactic spiral density wave using the method of spectral (periodogram) analysis. The tangential and radial perturbation amplitudes are f_\theta=6.0+/-2.6 km/s and f_R=7.2+/-2.2 km/s, respectively; the perturbation wavelengths are \lambda_\theta=3.2+/-0.5 kpc and \lambda_R=3.0+/-0.6 kpc for a four-armed spiral model, m=4. The phase of the Sun \chi_0 in the spiral density wave is -79^\circ+/-14^\circ and -199^\circ+/-16^\circ from the residual tangential and radial velocities, respectively. The most interesting result of this work is detecting a wave in vertical spatial velocities W versus distance R from the Galactic rotation axis. From the spectral analysis, we have found the following characteristics of this wave: the perturbation wavelength is \lambda_W=3.4+/-0.7 kpc and the amplitude f_W=4.3+/-1.2 km/s.