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

Smith, Alex and He, Jian-hua and Cole, Shaun and Stothert, Lee and Norberg, Peder and Baugh, Carlton and Bianchi, Davide and Wilson, Michael J. and Brooks, David and Forero-Romero, Jaime E. and Moustakas, John and Percival, Will J. and Tarle, Gregory and Wechsler, Risa H. (2019) 'Correcting for fibre assignment incompleteness in the DESI Bright Galaxy Survey.', Monthly notices of the Royal Astronomical Society., 484 (1). pp. 1285-1300.


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.

Item Type:Article
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Publisher statement:© 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.
Date accepted:21 December 2018
Date deposited:11 April 2019
Date of first online publication:09 January 2019
Date first made open access:11 April 2019

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