Tailoring Strong Lensing Cosmographic Observations

TL;DR

This paper explores optimizing spectroscopic followup and understanding systematics in strong lensing time delay cosmography to improve dark energy constraints, providing strategies for resource allocation and systematic mitigation.

Contribution

It introduces a code for optimizing spectroscopic resource allocation and analyzes the impact of systematics on cosmological parameter estimation in strong lensing.

Findings

Optimizing lens redshift distribution improves dark energy figure of merit by 40%.

Systematics levels significantly influence cosmological parameter accuracy.

Guidelines for selecting double vs quad image systems based on systematic differences.

Abstract

Strong lensing time delay cosmography has excellent complementarity with other dark energy probes, and will soon have abundant systems detected. We investigate two issues in the imaging and spectroscopic followup required to obtain the time delay distance. The first is optimization of spectroscopic resources. We develop a code to optimize the cosmological leverage under the constraint of constant spectroscopic time, and find that sculpting the lens system redshift distribution can deliver a 40% improvement in dark energy figure of merit. The second is the role of systematics, correlated between different quantities of a given system or model errors common to all systems. We show how the levels of different systematics affect the cosmological parameter estimation, and derive guidance for the fraction of double image vs quad image systems to follow as a function of differing systematics between them.