Emission from Thermal Instabilities

Abstract

We present the results of numerical simulations of the growth of thermal instabilities in cooling flows. These simulations begin with 10⁷ – 10⁸K gas and follow the evolution of the instability as the gas cools to a terminal temperature of 10⁴K. Only perturbations larger than 1 kpc develop shocks in the hot environment of cooling flows. These large perturbations evolve through three distinct phases: (l) the formation of a cold core, (2) a supersonic accretion phase onto the cold core, and (3) a subsonic accretion phase. We present the optical and ultraviolet line emission produced during the supersonic accretion phase. The emission lines have a lower luminosity and higher ionization level than the observed optical emission in cooling flows. These shocked condensations are a strong source of high ionization lines which may be detectable in the ultraviolet.