Analysis of galaxy kinematics based on Cepheids from the Gaia DR2 Catalogue

Abstract

ABSTRACT To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalogue are used in large part. Our working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at the solar distance is V0 = 240 ± 3 km s−1. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be R0 = 8.27 ± 0.10 kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at the present time and in the past. Therefore, the value of the wavelength λR, θ is in the range [2.4–3.0] kpc, the pitch angle iR, θ is in the range [−13○, −10○] for a four-arm pattern model, and the amplitudes of the radial and tangential perturbations are fR ∼ 12 km s−1 and fθ ∼ 9 km s−1, respectively. Velocities of Cepheids older than 120 Myr currently give a wavelength λR, θ ∼ 5 kpc. This value differs significantly from the one we obtained from samples of young Cepheids. An analysis of the positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength λR, θ = 2.7 kpc and amplitudes of radial and tangential perturbations fR = 7.9 km s−1 and fθ = 5 km s−1, respectively.