| Abstract : | The vertical density distribution of stars in a galactic disc is traditionally obtained assuming an isothermal vertical velocity dispersion of stars. But recent observed data from Gaia, LAMOST, RAVE show that this dispersion increases with height from the mid-plane. We theoretically study the dynamical effects of such non-isothermal dispersion on the vertical distribution of the thin disc stars in the Galaxy. We apply a linear gradient of +6.7 km/s/kpc in the dispersion values based on the observed data. We find that the mid-plane density is lower, and the scale height is higher in the
non-isothermal case than the corresponding values for the isothermal distribution, by ~35% in the solar neighbourhood for a stars-alone disc. The non-isothermal distribution shows a wing at high z, in agreement with observations, and is fitted well by a double sech^2, which could be mis-interpreted as the existence of a second, thicker disc, specially in external galaxies. Further, the total mid-plane density i.e, the Oort limit value, calculated using the realistic multi-component system of stars, gas in the field of dark matter halo, is reduced by 16% in the non-isothermal model. For details of this work, see- Sarkar & Jog, MNRAS, 499, 2523 (2020). |
