Skip to main content

Research Repository

Advanced Search

Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey

Smith, Alex; He, Jian-hua; Cole, Shaun; Stothert, Lee; Norberg, Peder; Baugh, Carlton; Bianchi, Davide; Wilson, Michael J; Brooks, David; Forero-Romero, Jaime E; Moustakas, John; Percival, Will J; Tarle, Gregory; Wechsler, Risa H

Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey Thumbnail


Alex Smith

Jian-hua He

Lee Stothert

Davide Bianchi

Michael J Wilson

David Brooks

Jaime E Forero-Romero

John Moustakas

Will J Percival

Gregory Tarle

Risa H Wechsler


The Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) will be a survey of bright, low-redshift galaxies, which is planned to cover an area of ∼14000 square degrees in three passes. Each pass will cover the survey area with ∼2000 pointings, each of area ∼8 square degrees. The BGS is currently proposed to consist of a bright high priority sample to an r-band magnitude limit r ∼ 19.5, with a fainter low priority sample to r ∼ 20. The geometry of the DESI fibre positioners in the focal plane of the telescope affects the completeness of the survey and has a non-trivial impact on clustering measurements. Using a BGS mock catalogue, we show that completeness due to fibre assignment primarily depends on the surface density of galaxies. Completeness is high (>95 per cent) in low-density regions, but very low (<10 per cent) in the centre of massive clusters. We apply the pair inverse probability (PIP) weighting correction to clustering measurements from a BGS mock which has been through the fibre assignment algorithm. This method is only unbiased if it is possible to observe every galaxy pair. To facilitate this, we randomly promote a small fraction of the fainter sample to be high priority, and dither the set of tile positions by a small angle. We show that inverse pair weighting combined with angular upweighting provides an unbiased correction to galaxy clustering measurements for the complete three pass survey, and also after one pass, which is highly incomplete.


Smith, A., He, J., Cole, S., Stothert, L., Norberg, P., Baugh, C., …Wechsler, R. H. (2019). Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey. Monthly Notices of the Royal Astronomical Society, 484(1), 1285-1300.

Journal Article Type Article
Acceptance Date Dec 21, 2018
Online Publication Date Jan 9, 2019
Publication Date Mar 31, 2019
Deposit Date Apr 11, 2019
Publicly Available Date Apr 11, 2019
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 484
Issue 1
Pages 1285-1300


Published Journal Article (5.8 Mb)

Copyright Statement
© 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.

You might also like

Downloadable Citations