Galactic rotation curves of spiral galaxies and dark matter in $f(\mathcal{R},T)$ gravity theory

Galactic rotation curve is a powerful indicator of the state of the gravitational field within a galaxy. Flatness of these curves implies the linear increase of mass to have constant velocity with the radial distance. In this paper, we focus on the possibility of explaining the flatness of observed rotation curves of spiral galaxies without postulating the existence of dark matter in the framework of $f(\mathcal{R},T)$ gravity where the gravitational Lagrangian is written by an arbitrary function of $\mathcal{R}$, the Ricci scalar and of $T$, the trace of stress-energy tensor $T_{\mu\nu}$. We derive the gravitational field equations in this gravity theory for the static spherically symmetric spacetime and solve the equations for metric coefficients using a specific model that has minimal coupling between matter and geometry. The orbital motion of a massive test particle moving in a stable circular orbit is considered and the behaviour of tangential velocity in the halo region with the help of the considered model is studied. The linear variation with distance of the interaction mass generated due to matter-geometry coupling successfully explains the galactic dynamics without the existence of dark matter at large distances from the galactic core.Comment: 13 pages, 4 figure