Optimising Spectroscopic and Photometric Galaxy Surveys: Same-sky Benefits for Dark Energy and Modified Gravity

Abstract

The combination of multiple cosmological probes can produce measurements of cosmological parameters much more stringent than those possible with any individual probe. We examine the combination of two highly correlated probes of late-time structure growth: (i) weak gravitational lensing from a survey with photometric redshifts and (ii) galaxy clustering and redshift space distortions from a survey with spectroscopic redshifts. We choose generic survey designs so that our results are applicable to a range of current and future photometric redshift (e.g. KiDS, DES, HSC, Euclid) and spectroscopic redshift (e.g. DESI, 4MOST, Sumire) surveys. Combining the surveys greatly improves their power to measure both dark energy and modified gravity. An independent, non-overlapping combination sees a dark energy figure of merit more than 4 times larger than that produced by either survey alone. The powerful synergies between the surveys are strongest for modified gravity, where their constraints are orthogonal, producing a non-overlapping joint figure of merit nearly 2 orders of magnitude larger than either alone. Our projected angular power spectrum formalism makes it easy to model the cross-correlation observable when the surveys overlap on the sky, producing a joint data vector and full covariance matrix. We calculate a same-sky improvement factor, from the inclusion of these cross-correlations, relative to non-overlapping surveys. We find nearly a factor of 4 for dark energy and more than a factor of 2 for modified gravity. The exact forecast figures of merit and same-sky benefits can be radically affected by a range of forecasts assumption, which we explore methodically in a sensitivity analysis. We show that that our fiducial assumptions produce robust results which give a good average picture of the science return from combining photometric and spectroscopic surveys.

22 pages, 8 figures

References in corpus (13)

• Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements
• Calibrating Redshift Distributions Beyond Spectroscopic Limits with Cross-Correlations
• DESI and other dark energy experiments in the era of neutrino mass measurements
• Current constraints on the cosmic growth history
• Optimal Surveys for Weak Lensing Tomography
• On the complementarity of galaxy clustering with cosmic shear and flux magnification
• The WiggleZ Dark Energy Survey: measuring the cosmic growth rate with the two-point galaxy correlation function
• Investigating Emission Line Galaxy Surveys with the Sloan Digital Sky Survey Telescope
• A Prescription for Galaxy Biasing Evolution as a Nuisance Parameter
• Are the halo occupation predictions consistent with large scale galaxy clustering?
• Using Cross-Correlations to Calibrate Lensing Source Redshift Distributions: Improving Cosmological Constraints from Upcoming Weak Lensing Surveys
• Redshift-space distortions from the cross-correlation of photometric populations
• Optimising Spectroscopic and Photometric Galaxy Surveys: Efficient Target Selection and Survey Strategy

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• A Precise Photometric Ratio via Laser Excitation of the Sodium Layer I: One-photon Excitation Using 342.78 nm Light
• Combining spectroscopic and photometric surveys using angular cross-correlations III: Galaxy bias and stochastisity