Effect of inelastic electron-atom collisions on the Balmer decrement

We have calculated the Balmer decrement in radiatively ionized hydrogen gas as a function of temperature and density, taking into account the effect of electron-atom collisions. It is found that once the electron density exceeds 1010 significant deviations from the normal radiative recombination decrement begin to occur. Implications of these results for the physical conditions in the line emitting region of the Seyfert galaxy NGC 4131 are discussed briefly. Subject headings: atomic processes - galaxies, individual - Seyfert galaxies