Blue and near-infrared surface photometry of spiral structure in 34 nonbarred grand design and flocculent galaxies

Abstract

Blue and near-infrared surface photometry has been used to measure disk scale lengths, spiral arm amplitudes, and spiral arm color variations in 34 spiral galaxies. Blue and near-infrared disk scale lengths are found to be similar within each galaxy. The color and amplitude variations in azimuthal profiles of galaxies correlate with the morphology of the spiral structure. Flocculent galaxies have very weak arms in the infrared. When these arms are strong in the blue, most of the structure in the galaxies are from star formation. When the blue arms are also weak, the flocculent structure arises from weak stellar density ripples. Extreme grand design galaxies have strong near-infrared arms which must be nearly pure stellar density enhancements. The blueness of a spiral arm compared to the interarm region in a grand design or intermediate type galaxy appears to be independent of the amplitude of the arm.