Galaxy And Mass Assembly (GAMA): Spectroscopic analysis
  The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric
and spectroscopic survey, using the AAOmega spectrograph on the
Anglo-Australian Telescope to obtain spectra for up to ~300000 galaxies over
280 square degrees, to a limiting magnitude of r_pet < 19.8 mag. The target
galaxies are distributed over 0<z<0.5 with a median redshift of z~0.2, although
the redshift distribution includes a small number of systems, primarily
quasars, at higher redshifts, up to and beyond z=1. The redshift accuracy
ranges from sigma_v~50km/s to sigma_v~100km/s depending on the signal-to-noise
of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis
pipeline. We present the steps involved in taking the raw two-dimensional
spectroscopic images through to flux-calibrated one-dimensional spectra. The
resulting GAMA spectra cover an observed wavelength range of 3750<lambda<8850 A
at a resolution of R~1300. The final flux calibration is typically accurate to
10-20%, although the reliability is worse at the extreme wavelength ends, and
poorer in the blue than the red. We present details of the measurement of
emission and absorption features in the GAMA spectra. These measurements are
characterised through a variety of quality control analyses detailing the
robustness and reliability of the measurements. We illustrate the quality of
the measurements with a brief exploration of elementary emission line
properties of the galaxies in the GAMA sample. We demonstrate the luminosity
dependence of the Balmer decrement, consistent with previously published
results, and explore further how Balmer decrement varies with galaxy mass and
redshift. We also investigate the mass and redshift dependencies of the
[NII]/Halpha vs [OIII]/Hbeta spectral diagnostic diagram, commonly used to
discriminate between star forming and nuclear activity in galaxies.
