= Disk scale height
{title2=$H$}
The \b[<disk scale height>] measures the vertical spread of matter or <pressure>. For an isothermal, non-self-gravitating <thin disk>, $\rho(z)=\rho_0\exp[-z^2/(2H^2)]$ and $H=c_s/\Omega_z$. Stronger vertical <gravity> confines the same gas more tightly; a higher <sound speed> makes it thicker. Here $H$ is a standard deviation, not a sharp surface; a polytropic surface uses a different convention.<Dynamics of Astrophysical Discs by Gordon I. Ogilvie>[Lecture7, sections7.1–7.2: Gaussian and second-moment definitions]{ref}
Back to article page
