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Astron. Astrophys. 333, 399-410 (1998)

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Cooling limits on galaxy formation

Gas dynamical simulations incorporating a background UV field and metal enrichment

Daniel Källander and John Hultman

Uppsala Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden (e-mail: pohlman@astro.uu.se)

Received 26 February 1997 / Accepted 25 November 1997


We present hydrodynamical simulations of the formation of galaxies in the mass range [FORMULA], with the focus on the efficiency of gas cooling.

The effect of a background UV radiation field, and the effect of metal enrichment of halo gas due to star formation and stellar evolution, are investigated. A background radiation field is found to strongly suppress the formation of galaxies with circular velocities less than [FORMULA] km/s. The effect is, however, not large enough to reconcile hierarchical clustering models with observations.

Metal enrichment of the halo gas increases the cooling rate at low redshifts. We find that the mass fraction of gas at virial temperatures may be reduced by a factor of two, in simulations with a UV background field added. The decrease in overall efficiency of gas cooling due to the inclusion of a UV background field can be more than compensated for by the increased cooling that follows metal enrichment of halo gas, but the effect may depend strongly on the assumed model of metal enrichment.

Key words: galaxies: formation – cooling flows – hydrodynamics – methods: numerical

Send offprint requests to: J. Hultman

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998