Local Jeans estimates of the Galaxy’s circular velocity, based on RGB stars from the Gaia catalogue

ABSTRACT The study investigates estimates of the circular velocity of the Milky Way reconstructed using different prescriptions for the density of tracer stars. The analysis is based on the Jeans equation and employs red giant branch (RGB) stars. The spatial density of the tracer population is specified in two ways: either via an analytical exponential profile or directly from observed star counts in neighboring volumes of identical geometry. It is shown that the use of an analytical density profile leads to a smoother circular velocity curve $V_{\rm cir}(R)$, consistent in shape with previously published results. In contrast, employing a local density estimated from star counts reveals systematic azimuthal variations in the local Jeans-based estimates of the circular velocity. In the radial range $R\ \approx\ 6{\text{-}}15$ kpc, differences between local curves $V_{\rm cir}(R,\Theta)$ are found to reach ${\sim} 10{\text{-}}15$ $\rm km\, s^{-1}$, depending on the azimuth. The observed density is not interpreted as an exact reconstruction of the true density distribution of RGB stars, since it may retain residual effects of the selection function, interstellar extinction, and population mixing. A comparison of the two approaches demonstrates that circular velocity estimates derived from the Jeans equation are sensitive to the adopted description of the tracer density. Under conditions of incomplete and non-uniform coverage of the Galactic disc, the Jeans equation can be regarded not only as a tool for constructing a single global relation $V_{\mathrm{cir}}(R)$, but also as a means of obtaining local dynamical estimates that are sensitive to potential non-axisymmetry in the Galactic disc.