Mapping the kinematic parameters of the Galaxy from the Gaia EDR3 red giants and sub-giants

Abstract

ABSTRACT We present the results of a kinematic analysis of red giants and sub-giants whose centroids are in the plane of our Galaxy. For this, the positions, parallaxes, proper motions, and radial velocities of these stars from the Gaia EDR3 catalogue were used. We applied two approaches to obtain kinematic parameters. The first approach – solving the equations of the Ogorodnikov–Milne model with respect to 12 unknowns – is generally accepted, but has a number of disadvantages. The second approach applied by us is to find the Galactocentric centroid velocity components and their partial derivatives with respect to coordinates from the solution of formal equations for the scalar stellar velocity field. To calculate the kinematic parameters by the methods mentioned above, same stellar samples were used. From these samples spherical regions with a radius of 1 kpc were selected, the centers of which were located strictly in the Galactic mid-plane at the nodes of the coordinate grid (xgal, ygal) of a rectangular Galactocentric coordinate system with step 100 pc. The investigated region of the Galaxy is located approximately in coordinate ranges 120° < θ < 240°, 0 kpc <R < 16 kpc, –1 kpc <z <1 kpc. We show the behaviour of kinematic parameters depending on the Galactocentric coordinates. The kinematic parameters as a function of Galactic coordinates were derived for the first time. Also, for the first time, the parameters ∂VR/∂θ and ∂Vθ/∂θ were derived.