Galaxy And Mass Assembly (GAMA): spectroscopic analysis

Abstract

The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic
\nsurvey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain
\nspectra for up to _ 300 000 galaxies over 280 square degrees, to a limiting magnitude of
\nrpet < 19.8mag. The target galaxies are distributed over 0 < z . 0.5 with a median redshift
\nof z _ 0.2, although the redshift distribution includes a small number of systems, primarily
\nquasars, at higher redshifts, up to and beyond z = 1. The redshift accuracy ranges from
\nσv _ 50 kms−1 to σv _ 100 kms−1 depending on the signal-to-noise of the spectrum. Here
\nwe describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps
\ninvolved in taking the raw two-dimensional spectroscopic images through to flux-calibrated
\none-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range
\nof 3750 . λ . 8850 °A at a resolution of R _ 1300. The final flux calibration is typically
\naccurate to 10 − 20%, although the reliability is worse at the extreme wavelength ends, and
\npoorer in the blue than the red. We present details of the measurement of emission and absorption
\nfeatures in the GAMA spectra. These measurements are characterised through a variety
\nof quality control analyses detailing the robustness and reliability of the measurements. We
\nillustrate the quality of the measurements with a brief exploration of elementary emission line
\nproperties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence
\nof the Balmer decrement, consistent with previously published results, and explore further
\nhow Balmer decrement varies with galaxy mass and redshift. We also investigate the mass
\nand redshift dependencies of the [NII]/Hα vs [OIII]/Hβ spectral diagnostic diagram, commonly
\nused to discriminate between star forming and nuclear activity in galaxies.