THE STAR-FORMATION LAW IN DISK GALAXIES - A BAYESIAN VIEW

The dependence of the star formation rate Psi proportional to g(x)/r(y ) on gas surface density g and galactocentric radius r are studied in disk galaxies. The sample includes the Milky Way galaxy and 11 nearby Sb and Sc galaxies with known radial gas surface densities and H alpha surface brightnesses, used as a measure of the SFR. The Bayesian appr oach permits to compute genuine probabilities for the validity of seve ral different functional forms. We do not find any significant explici t dependence of the SFR on radius. A linear dependence on gas density Psi proportional to g is found to be an order of magnitude more probab le than any universal non-linear law. If each galaxy has its own expon ent x, the non-linear law Psi proportional to g(x) would also be highl y probable. These findings are fairly independent of the CO-H-2 conver sion recipe used.