SARCS strong-lensing galaxy groups

Abstract

Aims.Various studies have shown a lensing bias in the mass-concentration relation of cluster-scale structures that is the result of an alignment of the major axis and the line of sight. In this paper, we aim to study this lensing bias through the mass-concentration relation of galaxy groups, thus extending observational constraints to dark matter haloes of mass ∼1013 −10 14 M . Methods. Our work is based on the stacked weak-lensing analysis of a sample of 80 strong-lensing galaxy groups. By combining several lenses, we significantly increase the signal-to-noise ratio of the lensing signal, thus providing constraints on the mass profile that cannot be obtained for individual objects. The resulting shear profiles were fitted with various mass models, among them the Navarro-Frank-White (NFW) profile, which provides an estimate of the total mass and of the concentration of the composite galaxy groups.Results. The main results of our analysis are the following: (i) the lensing signal does not allow us to firmly distinguish between a simple singular isothermal sphere mass distribution and the expected NFW mass profile; (ii) we obtain an average concentration c 200 = 8.6+2.1 −1.3 that is much higher than the value expected from numerical simulations for the corresponding average mass M 200 = 0.73−0.10 × 10 14 M ; (iii) the combination of our results with those at larger mass scales gives a mass-concentration relation c(M) of more than two decades in mass, whose slope disagrees with predictions from numerical simulations using unbiased populations of dark matter haloes; (iv) our combined c(M) relation matches results from simulations that only used haloes with a large strong-lensing cross-section, that is, elongated with a major axis close to the line of sight; (v) for the simplest case of prolate haloes, we estimate a lower limit on the minor-to-major axis ratio a/c = 0.5 for the average SARCS galaxy group with a toy model. Conclusions. Our analysis based on galaxy groups confirmed the results obtained at larger mass scales: strong lenses apparently present concentrations that are too high, which arises because the triaxial haloes are preferentially oriented with the line of sight. Because more massive systems already have large lensing cross-sections, they do not require a strong elongation along the line of sight, contrary to less massive galaxy groups. Therefore it is natural to observe higher lensing (projected) concentrations for such systems, resulting in an overall mass-concentration relation steeper than that of nonlensing haloes.

Weak-lensing-inferred scaling relations of galaxy clusters in the RCS2: mass-richness, mass-concentration, mass-bias, and more

“…The question of whether clusters are over-concentrated with respect to simulations has received considerable attention in recent years (e.g. Umetsu et al 2011;King & Mead 2011;Oguri et al 2012;Auger et al 2013;Foëx et al 2014;Umetsu et al 2014). Most of these works focus on strong lensing systems, which are expected to have higher projected concentrations than typical clusters of similar mass and redshift (Hennawi et al 2007;Oguri et al 2009Oguri et al , 2012.…”

Combining strong lensing and dynamics in galaxy clusters: integrating MAMPOSSt within LENSTOOL

“…Assuming a dark matter halo at z = 0.44 with M 200 ≈ 1 × 10 14 M ⊙ the concentration is c 200 ≈ 4.0 (computed with the procedures of Duffy et al 2008). SL2S J02140-0535 has also been studied by Foëx et al (2014), who were able to constrain the scale radius and the concentration parameters of galaxy groups using stacking techniques. SL2S J02140-0535, with an Einstein radius of ∼7 ′′ , belong to their stack "R3", which was characterized to have c 200 ∼ 10 and M 200 ∼ 10 14 M ⊙ .…”

KILOPARSEC MASS/LIGHT OFFSETS IN THE GALAXY PAIR-Lyα EMITTER LENS SYSTEM SDSS J1011+0143*

“…Indeed, extensive studies of stronglensing events in field galaxies and relaxed galaxy groups have shown that in general light traces mass well within uncertainties in terms of the coincidence of centroids (Treu & Koopmans 2004;Koopmans et al 2006;Gavazzi et al 2007;Bolton et al 2008a;Dye et al 2008;Belokurov et al 2009;Limousin et al 2009;Suyu et al 2009;Jones et al 2010;Grillo & Christensen 2011;Brownstein et al 2012;Oguri et al 2012;Grillo et al 2013Grillo et al , 2014Sonnenfeld et al 2013;Foëx et al 2014;Newman et al 2015;Shu et al 2015). Furthermore, the smaller offsets in the more massive galaxy and opposite direction between offsets associated with individual lens galaxies in SDSS J1011+0143 cannot be properly explained without considering the relative motion of the two lens galaxies.…”

“…To date, approximately 100 group-scale strong lenses have been identified in the Cambridge And Sloan Survey Of Wide ARcs in the skY (CASSOWARY) Survey (Stark et al 2013), the Sloan Bright Arcs Survey (Kubo et al 2010), andthe Strong Lensing Legacy Survey-ARCS (SARCS) sample (More et al 2012), as well as other individual observations. No mass/light offsets have been reported in these group-scale lenses either, although some works explicitly fix the mass centroid to that of the light for systems with insufficient constraints (e.g., Dye et al 2008;Belokurov et al 2009;Limousin et al 2009;Suyu et al 2009;Jones et al 2010;Grillo & Christensen 2011;Oguri et al 2012;Grillo et al 2013Grillo et al , 2014Foëx et al 2014). Nevertheless, the nondetections suggest that these isolated lens galaxies and galaxy groups are substantially relaxed.…”