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

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

doi:10.1093/mnras/stu727

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

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

Authors

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

Á.R. López-Sánchez

J. Loveday

Professor Peder Norberg peder.norberg@durham.ac.uk
Professor

J. Peacock

A.S.G. Robotham

E.N. Taylor

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.

Citation

Baldry, I., Alpaslan, M., Bauer, A., Bland-Hawthorn, J., Brough, S., Cluver, M., …Taylor, E. (2014). Galaxy And Mass Assembly (GAMA): AUTOZ spectral redshift measurements, confidence and errors. Monthly Notices of the Royal Astronomical Society, 441(3), 2440-2451. https://doi.org/10.1093/mnras/stu727

Journal Article Type	Article
Publication Date	Jul 1, 2014
Deposit Date	Jun 3, 2014
Publicly Available Date	Jun 5, 2014
Journal	Monthly Notices of the Royal Astronomical Society
Print ISSN	0035-8711
Electronic ISSN	1365-2966
Publisher	Royal Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	441
Issue	3
Pages	2440-2451
DOI	https://doi.org/10.1093/mnras/stu727
Keywords	Methods: data analysis, Techniques: spectroscopic, Surveys.

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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.