A Comparison of Weak Lensing Measurements From Ground- and Space-Based Facilities

TL;DR

This study compares weak lensing measurements from ground-based Subaru and space-based HST data, highlighting their respective strengths and limitations in galaxy shape measurement, survey speed, and cluster detection.

Contribution

It provides an empirical comparison of ground- and space-based weak lensing data, quantifying measurement biases, survey efficiencies, and cluster detection capabilities.

Findings

Ground-based shear measurements achieve sub-percent bias for bright, large galaxies.

Space-based imaging offers higher galaxy density and better sensitivity to low-mass or high-redshift clusters.

Ground-based surveys are faster but less deep, affecting tomographic analysis.

Abstract

We assess the relative merits of weak lensing surveys, using overlapping imaging data from the ground-based Subaru telescope and the Hubble Space Telescope (HST). Our tests complement similar studies undertaken with simulated data. From observations of 230,000 matched objects in the 2 square degree COSMOS field, we identify the limit at which faint galaxy shapes can be reliably measured from the ground. Our ground-based shear catalog achieves sub-percent calibration bias compared to high resolution space-based data, for galaxies brighter than i'~24.5 and with half-light radii larger than 1.8". This selection corresponds to a surface density of ~15 galaxies per sq arcmin compared to ~71 per sq arcmin from space. On the other hand the survey speed of current ground-based facilities is much faster than that of HST, although this gain is mitigated by the increased depth of space-based imaging desirable for tomographic (3D) analyses. As an independent experiment, we also reconstruct the projected mass distribution in the COSMOS field using both data sets, and compare the derived cluster catalogs with those from X-ray observations. The ground-based catalog achieves a reasonable degree of completeness, with minimal contamination and no detected bias, for massive clusters at redshifts 0.2<z<0.5. The space-based data provide improved precision and a greater sensitivity to clusters of lower mass or at higher redshift.