Reducing Systematic Error in Weak Lensing Cluster Surveys

Abstract

Weak lensing provides an important route toward collecting samples of clusters of galaxies selected by mass. Subtle systematic errors in image reduction can compromise the power of this technique. We use the B-mode signal to quantify this systematic error and to test methods for reducing this error. We show that two procedures are efficient in suppressing systematic error in the B-mode:(1) refinement of the mosaic CCD warping procedure to conform to absolute celestial coordinates and (2) truncation of the smoothing procedure on a scale of 10 . Application of these procedures reduces the systematic error to 20% of its original amplitude. We provide an analytic expression for the distribution of the highest peaks in noise maps that can be used to estimate the fraction of false peaks in the weak-lensing κ-signal-to-noise ratio (S/N) maps as a function of the detection threshold. Based on this analysis, we select a threshold S/N = 4.56 for identifying an uncontaminated set of weak-lensing peaks in two test fields covering a total area of ∼3 deg 2 . Taken together these fields contain seven peaks above the threshold. Among these, six are probable systems of galaxies and one is a superposition. We confirm the reliability of these peaks with dense redshift surveys, X-ray, and imaging observations. The systematic error reduction procedures we apply are general and can be applied to future large-area weak-lensing surveys. Our high-peak analysis suggests that with an S/N threshold of 4.5, there should be only 2.7 spurious weak-lensing peaks even in an area of 1000 deg 2 , where we expect ∼2000 peaks based on our Subaru fields.

Two- and three-dimensional wide-field weak lensing mass maps from the Hyper Suprime-Cam Subaru Strategic Program S16A data

“…Such weak lensing mass maps provide an important means of studying the large-scale structure of the Universe as well as non-Gaussian features of the matter density field. For example, massive clusters of galaxies can be identified from peaks in mass maps (e.g., Miyazaki et al 2002Miyazaki et al , 2007Wittman et al 2006;Shan et al 2012;Utsumi et al 2014;Liu et al 2015). Correlations of mass maps with light maps constructed from galaxies and clusters of galaxies can reveal the connection between mass and light, by constraining mass-tolight ratios and galaxy biases (e.g., Hoekstra et al 2002;Okabe et al 2010;Jullo et al 2012;Chang et al 2016;Pujol et al 2016;Utsumi et al 2016).…”

HectoMAPping the Universe

“…Tests of the projected matter distribution revealed by weak lensing against the distribution derived from the redshift survey show that the galaxies trace the three-dimensional large-scale matter distribution throughout the redshift range of the survey (Geller et al 2005). Later using both the DLS map and a field observed in better seeing with the Subaru telescope, Geller et al (2010), Kurtz et al (2012), and Utsumi et al (2014) demonstrate that thresholds for reliable detection of massive clusters of galaxies based on lensing maps have been overly optimistic. These results are consistent with the conclusions of larger surveys (e.g.…”

X-Ray Temperatures, Luminosities, and Masses from XMM-Newton Follow-upof the First Shear-selected Galaxy Cluster Sample∗

“…More recently, two weak lensing detections near this position have been reported. Utsumi et al (2014), in their analysis of a Subaru Suprime camera observation of a part of the DLS field F2, and Miyazaki et al (2015), in their weak lensing analysis of a Subaru Hyper Suprime-Cam (HSC) observation covering all of the same DLS field, both find weak lensing detections that are within ∼ 1 ′ (but on opposite sides) of the corresponding X-ray source position (of B11). A nearby optical cluster (z ∼ 0.54, Ascaso et al 2014) is found to be approximately ∼ 1.5 ′ away from the X-ray source and possibly consistent with the Miyazaki et al (2015) weak lensing peak.…”