Optical Studies of Star Formation in Normal Spiral Galaxies: Radial Characteristics

Abstract

First results of a new, homogeneous CCD imaging survey of nearby southern spiral galaxies in V, I and Ha are presented. Elliptical aperture photometry has been used to determine the deprojected surface brightnesses as a function of galactocentric radius, and thus to trace the past and present star formation behaviour. From a sub-sample of nine mainly barred spirals, we find a couple of notable trends. Firstly, nearly all of the barred spirals show evidence of significant levels of ongoing star formation in the bulge, probably fed by gas inflow along the bar. Secondly, the disk Ha profiles are quite shallow compared with the broadband exponential disks, implying a relative insensitivity of the current star formation rate to the surface density of stars already formed. In both the bulge and the disk, the gas consumption timescales are such as to require gas replenishment, e.g. by radial inflow.