A multi-wavelength study of spiral structure in galaxies. I. General
  characteristics in the optical
  Different spiral generation mechanisms are expected to produce different
morphological and kinematic features. In this first paper in a series we
carefully study the parameters of spiral structure in 155 face-on spiral
galaxies, selected from the Sloan Digital Sky Survey, in the three $gri$ bands.
We use a method for deriving a set of parameters of spiral structure, such as
the width of the spiral arms, their fraction to the total galaxy luminosity and
their colour, which have not been properly studied before. Our method is based
on an analysis of a set of photometric cuts perpendicular to the direction of a
spiral arm. Based on the results of our study, we compare the main three
classes of spirals: grand design, multi-armed and flocculent. We conclude that:
i) for the vast majority of galaxies (86\%) we observe an increase of their arm
width with galactocentric distance; ii) more luminous spirals in grand design
galaxies exhibit smaller variations of the pitch angle with radius than less
luminous grand design spirals; iii) grand design galaxies show less difference
between the pitch angles of individual arms than multi-armed galaxies. Apart
from these distinctive features, all three spiral classes do not differ
significantly by their pitch angle, arm width, width asymmetry, and
environment. Wavelength dependence is found only for the arm fraction.
Therefore, observationally we find no strong difference (except for the view
and number of arms) between grand design, multi-armed and flocculent spirals in
the sample galaxies.
