EasyCritics I: Efficient detection of strongly-lensing galaxy groups and clusters in wide-field surveys

TL;DR

EasyCritics is a fast, efficient algorithm that detects strongly-lensing galaxy groups and clusters in wide-field surveys by modeling light as a tracer of mass, without relying on arc recognition.

Contribution

It introduces a novel, highly parallelized method that predicts critical curves from luminous red galaxies, enabling quick detection of lensing structures in large datasets.

Findings

Successfully identified known lenses in CFHTLS data

Detected a previously missed cluster with giant arc candidates

Operates in under 1 minute for 1 deg² with GPU acceleration

Abstract

We present EasyCritics, an algorithm to detect strongly-lensing groups and clusters in wide-field surveys without relying on a direct recognition of arcs. EasyCritics assumes that light traces mass in order to predict the most likely locations of critical curves from the observed fluxes of luminous red early-type galaxies in the line of sight. The positions, redshifts and fluxes of these galaxies constrain the idealized gravitational lensing potential as a function of source redshift up to five free parameters, which are calibrated on few known lenses. From the lensing potential, EasyCritics derives the critical curves for a given, representative source redshift. The code is highly parallelized, uses fast Fourier methods and, optionally, GPU acceleration in order to process large datasets efficiently. The search of a $\smash{1 \, \mathrm{deg}^2}$ field of view requires less than 1 minute on a modern quad-core CPU, when using a pixel resolution of $0.25''/\mathrm{px}$. In this first part of a paper series on EasyCritics, we describe the main underlying concepts and present a first demonstration on data from the Canada-France-Hawaii-Telescope Lensing Survey. We show that EasyCritics is able to identify known group- and cluster-scale lenses, including a cluster with two giant arc candidates that were previously missed by automated arc detectors.