Fueling starburst galaxies with gas-rich mergers

Abstract

The dynamics of gas are modeled in a merger of two disk/halo galaxies of equal mass using a hybrid N-body/gasdynamics code. Violent tidal forces acting on the disks draw out extended tails and trigger the formation of central bars. As such bars form, gas in the inner half of each disk loses most of its angular momentum through gravitational torques and falls into a compact cloud within the center of the galaxy. These nuclear gas clouds merge when their parent galaxies do, resulting in the rapid assembly of about 5 billion solar masses of gas, which may plausibly be identified with the large central clouds seen in CO observations of galaxies such as NGC 520. Violent star formation in such central gas clouds, which seems inevitable, offers a likely explanation for luminous IRAS galaxies and may contribute significantly to the central stellar populations of merger remnants. If some of the nuclear gas can continue to lose angular momentum, it may be able to fuel or even form a central black hole, resulting in a radio galaxy or possibly even a quasar.