Galaxy And Mass Assembly (GAMA): autoz spectral redshift measurements, confidence and errors

I. K. Baldry*, M. Alpaslan, A. E. Bauer, J. Bland-Hawthorn, S. Brough, M. E. Cluver, S. M. Croom, L. J. M. Davies, S. P. Driver, M. L. P. Gunawardhana, B. W. Holwerda, A. M. Hopkins, L. S. Kelvin, J. Liske, A. R. Lopez-Sanchez, J. Loveday, P. Norberg, John Peacock, A. S. G. Robotham, E. N. Taylor

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The Galaxy And Mass Assembly (GAMA) survey has obtained spectra of over 230 000 targets using the Anglo-Australian Telescope. To homogenize the redshift measurements and improve the reliability, a fully automatic redshift code was developed (autoz). The measurements were made using a cross-correlation method for both the absorption- and the emission-line spectra. Large deviations in the high-pass-filtered spectra are partially clipped in order to be robust against uncorrected artefacts and to reduce the weight given to single-line matches. A single figure of merit (FOM) was developed that puts all template matches on to a similar confidence scale. The redshift confidence as a function of the FOM was fitted with a tanh function using a maximum likelihood method applied to repeat observations of targets. The method could be adapted to provide robust automatic redshifts for other large galaxy redshift surveys. For the GAMA survey, there was a substantial improvement in the reliability of assigned redshifts and in the lowering of redshift uncertainties with a median velocity uncertainty of 33 km s(-1).

Original languageEnglish
Pages (from-to)2440-2451
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume441
Issue number3
DOIs
Publication statusPublished - 1 Jul 2014

Keywords

  • methods: data analysis
  • techniques: spectroscopic
  • surveys
  • DIGITAL SKY SURVEY
  • OSCILLATION SPECTROSCOPIC SURVEY
  • SDSS-III
  • RADIAL-VELOCITIES
  • DATA REDUCTION
  • DATA RELEASE
  • SPECTROGRAPH
  • CATALOG

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