Tidally compressed molecular gas in ultraluminous and early type galaxies

Abstract

The effect of the galactic tidal field is usually considered disruptive in the literature. However, in some cases its effect can become compressive. Using the virial theorem, we have determined the minimum density for a cloud to be stable and gravitationally bound within the tidally compressive region of a galaxy. We have applied our results to a sample of early type and ultraluminous galaxies observed in the literature. For early type galaxies with a core-type luminosity profile, the molecular gas is compressed to high densities of at least 104cm-3 within the inner 50 pc where the field is compressive. For ultraluminous galaxies our treatment predicts molecular gas densities of 102 - 104cm-3 within the central few 100 pc. These values agree well with gas densities observed in the centers of these galaxies.