Thin and thick stellar disks in NGC 551

Abstract

The Milky Way contains two stellar disks: a thin disk extending to a height of a few hundred parsecs and a thick disk extending to a height of a few kiloparsecs. Understanding galactic structure helps us comprehend the evolutionary processes that shaped the galaxy into its current form. The vertical stability of a galactic disk depends on the balance between gravitational forces and pressure gradients. Theoretically, the disk’s vertical structure can be calculated by solving the coupled Poisson-Jeans equations. The gravitational component is interpreted through observed mass (from optical and radio observations), while pressure is estimated from observed velocity dispersion. Within the galactic disk, stellar mass contributes significantly to the total mass, which is balanced by stellar velocity dispersion. Therefore, solving the Poisson-Jeans equations requires information about both stellar surface density and velocity dispersion.