| Abstract : | We studied the vertical structure of the Galactic stellar disc using realistic theoretical model,
motivated by recent observations. The Galactic disc was modeled as a gravitationally coupled,
multi-component system of stars and gas (HI, H_2) embedded into the potential of a rigid, non-
responsive dark matter halo. We showed that the vertical stellar distribution is constrained toward
the Galactic mid-plane, mainly due to gas and dark matter halo gravity, in the inner and outer
Galaxy respectively, compared to a stars-alone case. Such a stellar disc is less likely to be disturbed by external tidal encounters. The disc scaleheight increased steeply with radius beyond R= 16 kpc, consistent with observations. We also studied how the constraining effect of gas affects the potential energy of the stellar disc. Recent observations from Gaia, LAMOST etc, show that the vertical velocity dispersion of stars increases along z, in the solar neighborhood, for the Galactic thin disc. We showed that this reduces the estimation of local dynamical mid-plane density, i.e, the Oort limit by 16%, compared to the traditional isothermal case. We also showed that the outer stellar disc, being a low density and vertically extended region, is affected by the radial variation in the rotation curve, planar velocity dispersion of stars, and orientation of the stellar velocity ellipsoid, altogether by ~30-40%. Therefore the complete Jeans and Poisson equations should be used in theoretical modeling, instead of the traditional sech^2 model, to account for those effects. We theoretically studied a dark matter halo dominated, low surface brightness galaxy (UGC 7321), and showed that the scaleheight increases with radius. Interestingly, its observed vertical density profile was modeled using a thin+thick disc in previous literature. Our model showed that invoking the thick disc is redundant here. |
