Mapping cluster mass distributions via gravitational lensing of background galaxies

Abstract

We present a new method for measuring the projected mass distributions of galaxy clusters, based solely on the gravitational lens amplification of background galaxies by the cluster potential field. The gravitational amplification is measured by comparing the joint distribution in redshift and magnitude of galaxies behind the cluster with that of the average distribution of field galaxies. Lensing shifts the magnitude distribution in a characteristic redshift-dependent way, and simultaneously dilutes the surface density of galaxies. These effects oppose, with the latter dominating at low redshift and the former at high redshift, owing to the curvature of the galaxy luminosity function. Lensing by a foreground cluster thus induces an excess of bright high-redshift galaxies, from which the lens amplification may be inferred.We show that the total amplification is directly related to the surface mass density in the weak field limit, and so it is possible to map the mass distribution of the cluster. The method is shown to be limited by discreteness noise and galaxy clustering behind the lens. Galaxy clustering sets a lower limit to the error along the redshift direction, but a clustering independent lensing signature may be obtained from the magnitude distribution at fixed redshift. Provided the luminosity function deviates from a pure power law, the lens-induced brightening can be measured directly by comparison with the field. In the limit that galaxy luminosities are independent of environment, this method is only shot-noise limited.Statistical techniques are developed for estimating the surface mass density of the cluster. We extend these methods to account for any obscuration by cluster halo dust, which may be mapped independently of the dark matter. We apply the method to a series of numerical simulations and show the the feasibility of the approach. We consider the use of approximate redshift information, and show how the mass estimates are degraded; finally we discuss the data required to map the dark matter in clusters from photometry alone.

LoCuSS: weak-lensing mass calibration of galaxy clusters

“…We do not assume any specific functions of n b because the background distribution is not constant, and may be depleted or boosted by a magnification bias (e.g. Broadhurst, Taylor & Peacock 1995;Umetsu et al 2011Umetsu et al , 2014Coupon, Broadhurst & Umetsu 2013). The second term in the bracket denotes the member galaxy distribution; B is the fraction, f (∆C) is the colour distribution and nm(r) is the radial distribution.…”

Simultaneous measurement of cosmology and intrinsic alignments using joint cosmic shear and galaxy number density correlations

“…In doing so we incorporate several cosmological signals which have been considered before as promising probes of cosmology themselves, including galaxy clustering from photometric redshift surveys (Blake & Bridle 2005;Dolney et al 2006;Zhan 2006;Blake et al 2007;Padmanabhan et al 2007) galaxy-galaxy lensing (e.g. Schneider & Rix 1997;Guzik & Seljak 2001Seljak 2002;Seljak et al 2005;Yoo et al 2006;Johnston et al 2007;Cacciato et al 2009) and lensing magnification (Broadhurst et al 1995;Zhang & Pen 2005, 2006van Waerbeke 2010). We follow the ansatz outlined in Bernstein (2009) and extend the investigation by Bridle & King (2007) who considered the residual information content in galaxy shape correlations after marginalising over the parameters of two loglinear grid models representing the II and GI terms.…”

Weak lensing power spectra for precision cosmology

“…This introduces cuts based on observed brightness and observed size, both of which are (de)magnified by lensing (e.g. Broadhurst et al 1995;Jain 2002), and will thus bias the sampling of the cosmic shear field.…”