Spiral arms in CALIFA galaxies traced by non-circular velocities,
  abundances, and extinctions
  We derive maps of the observed velocity of ionized gas, the oxygen abundance,
and the extinction (Balmer decrement) across the area of the four spiral
galaxies NGC36, NGC180, NGC6063, and NGC7653 from integral field spectroscopy
obtained by the Calar Alto Legacy Integral Field Area (CALIFA) survey. We
searched for spiral arms through Fourier analysis of the spatial distribution
of three tracers (non-circular motion, enhancement of the oxygen abundance, and
of the extinction) in the discs of our target galaxies. The spiral arms
(two-armed logarithmic spirals in the deprojected map) are shown in each target
galaxy for each tracer considered. The pitch angles of the spiral arms in a
given galaxy obtained with the three different tracers are close to each other.
The enhancement of the oxygen abundance in the spiral arms as compared to the
abundance in the interarm regions at a given galactocentric distance is small;
within a few per cent. We identified a metallicity gradient in our target
galaxies. Both barred galaxies in our sample show flatter gradients than the
two galaxies without bars. Galactic inclination, position angle of the major
axis, and the rotation curve were also obtained for each target galaxy using
the Fourier analysis of the two-dimensional velocity map.
