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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.

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


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

J. Peacock

A.S.G. Robotham

E.N. Taylor


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.


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.

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
Keywords Methods: data analysis, Techniques: spectroscopic, Surveys.


Published Journal Article (2.1 Mb)

Copyright Statement
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.

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