The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

(DES Collaboration)

doi:10.1093/mnras/staa1812

The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

(DES Collaboration)

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Abstract

Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to Az ∼ 0.04 in the weighted mean redshift of different redshift intervals (Az ∼ 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the Az = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

Original language	English
Pages (from-to)	4769-4786
Number of pages	18
Journal	Monthly Notices of the Royal Astronomical Society
Volume	496
Issue number	4
DOIs	https://doi.org/10.1093/mnras/staa1812
State	Published - Aug 1 2020

Funding

This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. Based in part on observations at Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation. The DES data management system is supported by the National Science Foundation under grants AST-1138766 and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588, SEV-2016-0597, and MDM-2015-0509, some of which include ERDF funds from the European Union. IFAE is partially funded by the CERCA program of the Gen-eralitat de Catalunya. Research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, and 306478. We acknowledge support from the Brazilian Instituto Nacional de Ciência e Tecnologia (INCT) e-Universe (CNPq grant 465376/2014-2). We thank Andrina Nicola for early consultant on spectra simulations. CC is supported by the Henry Luce Foundation. Funding for the DES Projects has been provided by the U.S. Department of Energy, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, the Center for Cosmology and AstroParticle Physics at the Ohio State University, the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Fi-nanciadora de Estudos e Projetos, Fundac¸ão Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência, Tecnologia e Inovac¸ão, the Deutsche Forschungsgemein-schaft and the Collaborating Institutions in the DES.

Funders	Funder number
Deutsche Forschungsgemein-schaft
European Union’s Seventh Framework Program
FP7/2007
Fermi Research Alliance, LLC	DE-AC02-07CH11359
Gen-eralitat de Catalunya
INCT
Kavli Institute of Cosmological Physics at the University of Chicago
Ministry of Science and Education of Spain
Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University
National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign
U.S. National Science Foundation
National Science Foundation	AST-1138766, AST-1536171
U.S. Department of Energy
Henry Luce Foundation
Office of Science
High Energy Physics
Ohio State University
Seventh Framework Programme	1138766, 240672, 306478, 291329
Higher Education Funding Council for England
Instituto Nacional de Ciência e Tecnologia Midas
Science and Technology Facilities Council
European Commission
European Research Council
Ministerio de Economía y Competitividad	SEV-2016-0588, SEV-2016-0597, ESP2015-66861, MDM-2015-0509, FPA2015-68048, AYA2015-71825
Conselho Nacional de Desenvolvimento Científico e Tecnológico	465376/2014-2
Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro
Financiadora de Estudos e Projetos
Ministério da Ciência e Tecnologia
European Regional Development Fund

Keywords

Distance scale
Galaxies: distances and redshifts
Galaxies: statistics
Gravitational lensing: weak
Large-scale structure of Universe

Access to Document

10.1093/mnras/staa1812

Cite this

@article{d69be8c614f346a5b09cea6d8bf0d218,

title = "The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys",

abstract = "Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to Az ∼ 0.04 in the weighted mean redshift of different redshift intervals (Az ∼ 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the Az = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.",

keywords = "Distance scale, Galaxies: distances and redshifts, Galaxies: statistics, Gravitational lensing: weak, Large-scale structure of Universe",

author = "{(DES Collaboration)} and Hartley, {W. G.} and C. Chang and S. Samani and {Carnero Rosell}, A. and Davis, {T. M.} and B. Hoyle and D. Gruen and J. Asorey and J. Gschwend and C. Lidman and K. Kuehn and A. King and Rau, {M. M.} and Wechsler, {R. H.} and J. DeRose and Hinton, {S. R.} and L. Whiteway and Abbott, {T. M.C.} and S. Allam and M. Aguena and J. Annis and S. Avila and Bernstein, {G. M.} and E. Bertin and Bridle, {S. L.} and D. Brooks and Burke, {D. L.} and {Carrasco Kind}, M. and J. Carretero and Castander, {F. J.} and R. Cawthon and M. Costanzi and {Da Costa}, {L. N.} and S. Desai and Diehl, {H. T.} and Dietrich, {J. P.} and B. Flaugher and P. Fosalba and J. Frieman and J. Garc{\'i}a-Bellido and E. Gaztanaga and Gerdes, {D. W.} and Gruendl, {R. A.} and G. Gutierrez and Hollowood, {D. L.} and K. Honscheid and James, {D. J.} and S. Kent and E. Krause and E. Suchyta",

note = "Publisher Copyright: {\textcopyright} 2020 The Author(s).",

year = "2020",

month = aug,

day = "1",

doi = "10.1093/mnras/staa1812",

language = "English",

volume = "496",

pages = "4769--4786",

journal = "Monthly Notices of the Royal Astronomical Society",

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publisher = "Oxford University Press",

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TY - JOUR

T1 - The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

AU - (DES Collaboration)

AU - Hartley, W. G.

AU - Chang, C.

AU - Samani, S.

AU - Carnero Rosell, A.

AU - Davis, T. M.

AU - Hoyle, B.

AU - Gruen, D.

AU - Asorey, J.

AU - Gschwend, J.

AU - Lidman, C.

AU - Kuehn, K.

AU - King, A.

AU - Rau, M. M.

AU - Wechsler, R. H.

AU - DeRose, J.

AU - Hinton, S. R.

AU - Whiteway, L.

AU - Abbott, T. M.C.

AU - Allam, S.

AU - Aguena, M.

AU - Annis, J.

AU - Avila, S.

AU - Bernstein, G. M.

AU - Bertin, E.

AU - Bridle, S. L.

AU - Brooks, D.

AU - Burke, D. L.

AU - Carrasco Kind, M.

AU - Carretero, J.

AU - Castander, F. J.

AU - Cawthon, R.

AU - Costanzi, M.

AU - Da Costa, L. N.

AU - Desai, S.

AU - Diehl, H. T.

AU - Dietrich, J. P.

AU - Flaugher, B.

AU - Fosalba, P.

AU - Frieman, J.

AU - García-Bellido, J.

AU - Gaztanaga, E.

AU - Gerdes, D. W.

AU - Gruendl, R. A.

AU - Gutierrez, G.

AU - Hollowood, D. L.

AU - Honscheid, K.

AU - James, D. J.

AU - Kent, S.

AU - Krause, E.

AU - Suchyta, E.

PY - 2020/8/1

Y1 - 2020/8/1

N2 - Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to Az ∼ 0.04 in the weighted mean redshift of different redshift intervals (Az ∼ 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the Az = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

AB - Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to Az ∼ 0.04 in the weighted mean redshift of different redshift intervals (Az ∼ 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the Az = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

KW - Distance scale

KW - Galaxies: distances and redshifts

KW - Galaxies: statistics

KW - Gravitational lensing: weak

KW - Large-scale structure of Universe

UR - http://www.scopus.com/inward/record.url?scp=85091661510&partnerID=8YFLogxK

U2 - 10.1093/mnras/staa1812

DO - 10.1093/mnras/staa1812

M3 - Article

AN - SCOPUS:85091661510

SN - 0035-8711

VL - 496

SP - 4769

EP - 4786

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 4

ER -

The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

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