Dark Energy Survey Year 1 Results: Redshift distributions of the weak lensing source galaxies

B. Hoyle , D. Gruen , G.M. Bernstein , M.M. Rau , J. de Vicente , W.G. Hartley , E. Gaztanaga , J. Derose , M.A. Troxel , C. Davis , A. Alarcon , N. Maccrann , J. Prat , C. Sánchez , E. Sheldon , R.H. Wechsler , J. Asorey , M.R. Becker , C. Bonnett , A. Carnero Rosell , D. Carollo , M. Carrasco Kind , F.J. Castander , R. Cawthon , C. Chang , M. Childress , T.M. Davis , A. Drlica-Wagner , M. Gatti , K. Glazebrook , J. Gschwend , S.R. Hinton , J.K. Hoormann , A.G. Kim , A. King , K. Kuehn , G. Lewis , C. Lidman , H. Lin , E. Macaulay , M.A.G. Maia , P. Martini , D. Mudd , A. Möller , R.C. Nichol , R.L.C. Ogando , R.P. Rollins , A. Roodman , A.J. Ross , E. Rozo , E.S. Rykoff , S. Samuroff , I. Sevilla-Noarbe , R. Sharp , N.E. Sommer , B.E. Tucker , S.A. Uddin , T.N. Varga , P. Vielzeuf , F. Yuan , B. Zhang , T.M.C. Abbott , F.B. Abdalla , S. Allam , J. Annis , K. Bechtol , A. Benoit-Lévy (1) , E. Bertin (1) , D. Brooks , E. Buckley-Geer , D.L. Burke , M.T. Busha , D. Capozzi , J. Carretero , M. Crocce , C.B. d'Andrea , L.N. da Costa , D.L. Depoy , S. Desai , H.T. Diehl , P. Doel , T.F. Eifler , J. Estrada , A.E. Evrard , E. Fernandez , B. Flaugher , P. Fosalba , J. Frieman , J. García-Bellido , D.W. Gerdes , T. Giannantonio , D.A. Goldstein , R.A. Gruendl , G. Gutierrez , K. Honscheid , D.J. James , M. Jarvis , T. Jeltema , M.W.G. Johnson , M.D. Johnson , D. Kirk , E. Krause , S. Kuhlmann , N. Kuropatkin , O. Lahav , T.S. Li , M. Lima , M. March , J.L. Marshall , P. Melchior , F. Menanteau , R. Miquel , B. Nord , C.R. O'Neill , A.A. Plazas , A.K. Romer , M. Sako , E. Sanchez , B. Santiago , V. Scarpine , R. Schindler , M. Schubnell , M. Smith , R.C. Smith , M. Soares-Santos , F. Sobreira , E. Suchyta , M.E.C. Swanson , G. Tarle , D. Thomas , D.L. Tucker , V. Vikram , A.R. Walker , J. Weller , W. Wester , R.C. Wolf , B. Yanny , J. Zuntz

1 IAP - Institut d'Astrophysique de Paris

We describe the derivation and validation of redshift distribution estimates and their uncertainties for the populations of galaxies used as weak-lensing sources in the Dark Energy Survey (DES) Year 1 cosmological analyses. The Bayesian Photometric Redshift (bpz) code is used to assign galaxies to four redshift bins between z ≈ 0.2 and ≈1.3, and to produce initial estimates of the lensing-weighted redshift distributions $$n^i_{\rm PZ}(z)\propto \mathrm{d}n^i/\mathrm{d}z$$ for members of bin i. Accurate determination of cosmological parameters depends critically on knowledge of n^i, but is insensitive to bin assignments or redshift errors for individual galaxies. The cosmological analyses allow for shifts $$n^i(z)=n^i_{\rm PZ}(z-\Delta z^i)$$ to correct the mean redshift of n^i(z) for biases in $$n^i_{\rm PZ}$$. The Δz^i are constrained by comparison of independently estimated 30-band photometric redshifts of galaxies in the Cosmic Evolution Survey (COSMOS) field to bpz estimates made from the DES griz fluxes, for a sample matched in fluxes, pre-seeing size, and lensing weight to the DES weak-lensing sources. In companion papers, the Δz^i of the three lowest redshift bins are further constrained by the angular clustering of the source galaxies around red galaxies with secure photometric redshifts at 0.15 < z < 0.9. This paper details the bpz and COSMOS procedures, and demonstrates that the cosmological inference is insensitive to details of the n^i(z) beyond the choice of Δz^i. The clustering and COSMOS validation methods produce consistent estimates of Δz^i in the bins where both can be applied, with combined uncertainties of $$\sigma_{\Delta z^i}=0.015, 0.013, 0.011,$$ and 0.022 in the four bins. Repeating the photo-z procedure instead using the Directional Neighbourhood Fitting algorithm, or using the n^i(z) estimated from the matched sample in COSMOS, yields no discernible difference in cosmological inferences.

Mots clés: methods: data analysis; catalogues; surveys

Domaines: Astrophysique [astro-ph]

B. Hoyle, D. Gruen, G.M. Bernstein, M.M. Rau, J. de Vicente, et al.. Dark Energy Survey Year 1 Results: Redshift distributions of the weak lensing source galaxies. Mon.Not.Roy.Astron.Soc., 2018, 478 (1), pp.592-610. ⟨10.1093/mnras/sty957⟩. ⟨hal-01802087⟩