A PHOTOMETRIC-METHOD FOR QUANTIFYING ASYMMETRIES IN DISK GALAXIES

A photometric method for quantifying deviations from axisymmetry in op tical images of disk galaxies is applied to a sample of 32 face-on and nearly face-on spirals. The method involves comparing the relative fl uxes contained within trapezoidal sectors arranged symmetrically about the galaxy center of light, excluding the bulge and/or barred regions . Such a method has several advantages over others, especially when qu antifying asymmetry in flocculent galaxies. Specifically, the averagin g of large regions improves the signal-to-noise in the measurements; t he method is not strongly affected by the presence of spiral arms; and it identifies the kinds of asymmetry that are likely to be dynamicall y important. Application of this ''method of sectors'' to R-band image s of 32 disk galaxies indicates that about 30% of spirals show deviati ons from axisymmetry at the 5 sigma level.