CALIFA, the Calar Alto Legacy Integral Field Area survey. II. First
  public data release
  We present the first public data release of the CALIFA survey. It consists of
science-grade optical datacubes for the first 100 of eventually 600 nearby
(0.005<z<0.03) galaxies, obtained with the integral-field spectrograph
PMAS/PPak mounted on the 3.5m telescope at the Calar Alto observatory. The
galaxies in DR1 already cover a wide range of properties in color-magnitude
space, morphological type, stellar mass, and gas ionization conditions. This
offers the potential to tackle a variety of open questions in galaxy evolution
using spatially resolved spectroscopy. Two different spectral setups are
available for each galaxy, (i) a low-resolution V500 setup covering the nominal
wavelength range 3745-7500A with a spectral resolution of 6.0A (FWHM), and (ii)
a medium-resolution V1200 setup covering the nominal wavelength range
3650-4840A with a spectral resolution of 2.3A (FWHM). We present the
characteristics and data structure of the CALIFA datasets that should be taken
into account for scientific exploitation of the data, in particular the effects
of vignetting, bad pixels and spatially correlated noise. The data quality test
for all 100 galaxies showed that we reach a median limiting continuum
sensitivity of 1.0x10^-18erg/s/cm^2/A/arcsec^2 at 5635A and
2.2x10^-18erg/s/cm^2/A/arcsec^2 at 4500A for the V500 and V1200 setup
respectively, which corresponds to limiting r and g band surface brightnesses
of 23.6mag/arcsec^2 and 23.4mag/arcsec^2, or an unresolved emission-line flux
detection limit of roughly 1x10^-17erg/s/cm^2/arcsec^2 and
0.6x10^-17erg/s/cm^2/arcsec^2, respectively. The median spatial resolution is
3.7", and the absolute spectrophotometric calibration is better than 15%
(1sigma). We also describe the available interfaces and tools that allow easy
access to this first public CALIFA data.
