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The origin of the steep vertical stellar distribition in the Galactic disk

Arunima Banerjee (Indian Institute of Science, Bangalore)

Over the past two decades observations have revealed that the vertical density distribution of stars in galaxies near the mid-plane is substantially steeper than the sech2 function that is expected from an isothermal approximation. However, the physical origin for this has not been explained so far. Here we show that such steep profiles result naturally even within the isothermal regime, on taking into account the gravitational force due to the gas. Due to its low velocity dispersion the gas is concentrated closer to the galactic mid-plane than the stars, and hence it strongly affects the vertical stellar distribution even though its contribution to the total surface density is small.