Target Selection and Sample Characterization for the DESI LOW-Z Secondary Target Program

Author:

Darragh-Ford EliseORCID,Wu John F.ORCID,Mao Yao-YuanORCID,Wechsler Risa H.ORCID,Geha MarlaORCID,Forero-Romero Jaime E.ORCID,Hahn ChangHoonORCID,Kallivayalil NityaORCID,Moustakas JohnORCID,Nadler Ethan O.ORCID,Nowotka Marta,Peek J. E. G.ORCID,Tollerud Erik J.ORCID,Weiner BenjaminORCID,Aguilar J.ORCID,Ahlen S.ORCID,Brooks D.ORCID,Cooper A. P.ORCID,de la Macorra A.,Dey A.ORCID,Fanning K.,Font-Ribera A.ORCID,Gontcho A Gontcho S.ORCID,Honscheid K.,Kisner T.ORCID,Kremin AnthonyORCID,Landriau M.ORCID,Levi Michael E.ORCID,Martini P.ORCID,Meisner Aaron M.ORCID,Miquel R.ORCID,Myers Adam D.,Nie JundanORCID,Palanque-Delabrouille N.ORCID,Percival W. J.ORCID,Prada F.ORCID,Schlegel D.ORCID,Schubnell M.,Tarlé GregoryORCID,Vargas-Magaña M.,Zhou ZhiminORCID,Zou H.ORCID

Abstract

Abstract We introduce the DESI LOW-Z Secondary Target Survey, which combines the wide-area capabilities of the Dark Energy Spectroscopic Instrument (DESI) with an efficient, low-redshift target selection method. Our selection consists of a set of color and surface brightness cuts, combined with modern machine-learning methods, to target low-redshift dwarf galaxies (z < 0.03) between 19 < r < 21 with high completeness. We employ a convolutional neural network (CNN) to select high-priority targets. The LOW-Z survey has already obtained over 22,000 redshifts of dwarf galaxies (M * < 109 M ), comparable to the number of dwarf galaxies discovered in the Sloan Digital Sky Survey DR8 and GAMA. As a spare fiber survey, LOW-Z currently receives fiber allocation for just ∼50% of its targets. However, we estimate that our selection is highly complete: for galaxies at z < 0.03 within our magnitude limits, we achieve better than 95% completeness with ∼1% efficiency using catalog-level photometric cuts. We also demonstrate that our CNN selections z < 0.03 galaxies from the photometric cuts subsample at least 10 times more efficiently while maintaining high completeness. The full 5 yr DESI program will expand the LOW-Z sample, densely mapping the low-redshift Universe, providing an unprecedented sample of dwarf galaxies, and providing critical information about how to pursue effective and efficient low-redshift surveys.

Funder

National Science Foundation

U.S. Department of Energy

Publisher

American Astronomical Society

Subject

Space and Planetary Science,Astronomy and Astrophysics

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