Redetermination of Galactic Spiral Density Wave Parameters Based on Spectral Analysis of Maser Radial Velocities

TL;DR

This study uses spectral analysis of maser radial velocities to refine parameters of the Galactic spiral density wave, revealing key characteristics like amplitude, wavelength, and pitch angle with improved accuracy.

Contribution

It introduces a spectrum reconstruction method based on maximum entropy to analyze maser data with large gaps, leading to more precise spiral density wave parameters.

Findings

Perturbation amplitude: 7.7 km/s

Wavelength: 2.2 kpc

Pitch angle: -5 degrees

Abstract

To redetermine the Galactic spiral density wave parameters, we have performed a spectral (Fourier) analysis of the radial velocities for 44 masers with known trigonometric parallaxes, proper motions, and line-of-sight velocities. The masers are distributed in a wide range of Galactocentric distances $(3.5<R<13.2$ kpc) and are characterized by a wide scatter of position angles $\theta$ in the Galactic XY plane. This has required an accurate allowance for the dependence of the perturbation phase both on the logarithm of the Galactocentric distances and on the position angles of the objects. To increase the significance of the extraction of periodicities from data series with large gaps, we have proposed and implemented a spectrum reconstruction method based on a generalized maximum entropy method. As a result, we have extracted a periodicity describing a spiral density wave with the following parameters from the maser radial velocities: the perturbation amplitude $f_R = 7.7^{+1.7}_{-1.5}$ km s$^{-1}$, the perturbation wavelength $\lambda=2.2^{+0.4}_{-0.1}$ kpc, the pitch angle of the spiral density wave $i=-5^{+0.2^\circ}_{-0.9^\circ}$, and the phase of the Sun in the spiral density wave $\chi_\odot= -147^{+3^\circ}_{-17^\circ}$.