Sample variance in photometric redshift calibration: cosmological biases and survey requirements

Abstract

We use N-body/photometric galaxy simulations to examine the impact of sample variance of spectroscopic redshift samples on the accuracy of photometric redshift (photo-z) determination and calibration of photo-z errors. We estimate the biases in the cosmological parameter constraints from weak lensing and derive requirements on the spectroscopic follow-up for three different photo-z algorithms chosen to broadly span the range of algorithms available. We find that sample variance is much more relevant for the photo-z error calibration than for photo-z training, implying that follow-up requirements are similar for different algorithms. We demonstrate that the spectroscopic sample can be used for training of photo-zs and error calibration without incurring additional bias in the cosmological parameters. We provide a guide for observing proposals for the spectroscopic follow-up to ensure that redshift calibration biases do not dominate the cosmological parameter error budget. For example, assuming optimistically (pessimistically) that the weak lensing shear measurements from the Dark Energy Survey could obtain 1-sigma constraints on the dark energy equation of state w of 0.035 (0.055), implies a follow-up requirement of 150 (40) patches of sky with a telescope such as Magellan, assuming a 1/8^2 deg effective field of view and 400 galaxies per patch. Assuming (optimistically) a VVDS-like spectroscopic completeness with purely random failures, this could be accomplished with about 75 (20) nights of observation. For more realistic assumptions regarding spectroscopic completeness, or in the presence of other sources of systematics not considered here, further degradations to dark energy constraints are possible. We test several approaches for reducing the requirements. Abridged

Accepted to MNRAS. Results and references added, format changed. 16 pages, 9 figures, 5 tables

References in corpus (15)

• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• Galaxies in the Hubble Ultra Deep Field: I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology
• Cosmology with Weak Lensing Surveys
• Calibrating Redshift Distributions Beyond Spectroscopic Limits with Cross-Correlations
• The Zurich Extragalactic Bayesian Redshift Analyzer (ZEBRA) and its first application: COSMOS
• Estimating the Redshift Distribution of Faint Galaxy Samples
• A Galaxy Photometric Redshift Catalog for the Sloan Digital Sky Survey Data Release 6
• Optimal Surveys for Weak Lensing Tomography
• The Role of Environment in the Mass-Metallicity Relation
• Redshift and Shear Calibration: Impact on Cosmic Shear Studies and Survey Design
• Size of spectroscopic calibration samples for cosmic shear photometric redshifts
• Characterizing and Propagating Modeling Uncertainties in Photometrically-Derived Redshift Distributions
• Kernel Regression For Determining Photometric Redshifts From Sloan Broadband Photometry
• Optimising cosmic shear surveys to measure modifications to gravity on cosmic scales
• Survey Requirements for Accurate and Precise Photometric Redshifts for Type Ia Supernovae

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• Lensing is Low: Cosmology, Galaxy Formation, or New Physics?
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• Photometric redshift analysis in the Dark Energy Survey Science Verification data
• Dark Energy Survey Year 3 Results: Redshift Calibration of the Weak Lensing Source Galaxies
• Redshift distributions of galaxies in the DES Science Verification shear catalogue and implications for weak lensing
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• Photometric Redshifts for Next-Generation Surveys
• Spectroscopic Needs for Imaging Dark Energy Experiments: Photometric Redshift Training and Calibration
• A Measurement of the Correlation of Galaxy Surveys with CMB Lensing Convergence Maps from the South Pole Telescope
• The 2-degree Field Lensing Survey: design and clustering measurements
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• General Requirements on Matter Power Spectrum Predictions for Cosmology with Weak Lensing Tomography
• Cosmology from large scale galaxy clustering and galaxy-galaxy lensing with Dark Energy Survey Science Verification data
• The Blanco Cosmology Survey: An Optically-Selected Galaxy Cluster Catalog and a Public Release of Optical Data Products
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• Exhausting the Information: Novel Bayesian Combination of Photometric Redshift PDFs
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• ADDGALS: Simulated Sky Catalogs for Wide Field Galaxy Surveys
• Photometric Redshift Calibration Requirements for WFIRST Weak Lensing Cosmology: Predictions from CANDELS
• Spectroscopic failures in photometric redshift calibration: cosmological biases and survey requirements
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• Probing cosmology and gastrophysics with fast radio bursts: Cross-correlations of dark matter haloes and cosmic dispersion measures
• Improved Mock Galaxy Catalogs for the DEEP2 Galaxy Redshift Survey from Subhalo Abundance and Environment Matching
• Optimising cosmic shear surveys to measure modifications to gravity on cosmic scales
• Analytic marginalization of $N(z)$ uncertainties in tomographic galaxy surveys
• Galaxy clustering with photometric surveys using PDF redshift information
• Simulation-based inference of deep fields: galaxy population model and redshift distributions
• Dark Energy Survey Year 3 Results: Redshift Calibration of the MagLim Lens Sample from the combination of SOMPZ and clustering and its impact on Cosmology
• The source-lens clustering effect in the context of lensing tomography and its self-calibration
• Cosmic Shear E/B-mode Estimation with Binned Correlation Function Data
• The Impact of Photometric Redshift Errors on Lensing Statistics in Ray-Tracing Simulations
• Mapping Variations of Redshift Distributions with Probability Integral Transforms