The star-formation efficiency and density of the disks of spiral galaxies

The four well studied spiral galaxies M33, M81, M100, and M101 are used to analyze the dependences of the star-formation rate (SFR) and star-formation efficiency (SFE = SFR/M _gas ) on galactocentric distance R and the photometric and some kinematic parameters of galactic disks. The dependences SFR(R) were estimated based on UV and far-infrared data using published extinction-corrected UV brightness profiles of the galaxies. The local SFE values are most closely related to the surface brightness (density) of the galactic disk at a given R, with this dependence being the same for all four galaxies (except for their central regions). In order to explain the observed disk densities in terms of a simple conservative model (“toy model”) for the evolution of the gas density, the local value of the parameter N in the Schmidt law for the disk (SFR ～ σ _gas ^N ) must not exceed unity. In this case, the observed dependences σ _gas (R) and SFE(R) can be matched assuming that accretion is occuring in the central regions of the disks.