Strong lensing in the MARENOSTRUM UNIVERSE

Abstract

Context. Strong lensing is one of the most direct probes of mass distribution in the inner regions of galaxy clusters. It can be used to constrain the density profiles and to measure the mass of the lenses. Moreover, the abundance of strong lensing events can be used to constrain structure formation and cosmological parameters through the so-called "arc-statistics" approach. However, several issues related to the use of strong lensing clusters in cosmological applications are still controversial, leading to the suspicion that several biases may affect this very peculiar class of objects. Aims. With this study we aim a better understanding of the properties of galaxy clusters that can potentially act as strong lenses. Methods. We do so by investigating the properties of a large sample of galaxy clusters extracted from the N-body/hydrodynamical simulation MareNostrum Universe. We perform ray-tracing simulations with each of them and identify those objects capable of producing strong lensing effects. We explore the correlation between the cross section for lensing and many properties of clusters, such as mass, three-dimensional and projected shapes, their concentrations, the X-ray luminosity, and the dynamical activity. Results. We quantify the minimal cluster mass required for producing both multiple images and large distortions. While we do not measure a significant excess of triaxiality in strong lensing clusters, we find that the probability of strong alignments between the major axes of the lenses and the line of sight is a growing function of the lensing cross section. In projection, the strong lenses appear rounder within R 200 , but we find that their cores tend to be more elliptical as the lensing cross section increases. As a result of the orientation bias, we also find that the cluster concentrations estimated from the projected density profiles tend to be biased high. The X-ray luminosity of strong lensing clusters tend to be higher than for normal lenses of similar mass and redshift. This is particularly significant for the least massive lenses. Finally, we find that the strongest lenses generally exhibit an excess of kinetic energy within the virial radius, thus indicating that they are more dynamically active than the usual clusters. Conclusions. We conclude that strong lensing clusters are a very peculiar class of objects, affected by many selection biases that need to be properly modeled when using them to study the inner structure of galaxy clusters or to constrain the cosmological parameters.

Comparison of an X-ray-selected sample of massive lensing clusters with the MareNostrum Universe ΛCDM simulation

“…A detailed description of the analysis performed on these objects can be found in Meneghetti et al (2010a) and in Fedeli et al (2010). We briefly summarize the most relevant aspects of the analysis here.…”

“…As explained in Meneghetti et al (2010a) and in Meneghetti et al (2003), the lensing cross sections are derived from the deflection angle maps, which are in turn calculated by means of ray-tracing methods (see also Meneghetti et al 2005a,b;Fedeli et al 2006). Bundles of light rays are traced from the observer position back to the source plane.…”

The strongest gravitational lenses

“…For instance, a very elongated halo that is directed along the line of sight can lead to a highly concentrated, projected surface mass-density profile, which causes a large tangential critical curve (see e.g. Oguri et al 2003;Dalal et al 2004;Meneghetti et al 2007Meneghetti et al , 2010. When sampling axis ratios from Eqs.…”

Characterizing strong lensing galaxy clusters using the Millennium-XXL and moka simulations

“…The robustness of this definition has already been tested and discussed in a series of works (Meneghetti et al 2008(Meneghetti et al , 2010aRedlich et al 2012;Giocoli et al 2014) to which we remind the reader for more details. The size of the Einstein radius defines a measure of the strong lensing region and, for an axially symmetric lens, permits to estimate the mass enclosed within it using the equation:…”

“…Given the significance of SLCs, characterising this peculiar class of object is crucial and this has been the focus of many studies (for example : Hennawi et al 2007;Meneghetti et al 2010a;Redlich et al 2012;Waizmann et al 2012). This is also the motivation of the present work, where we aim at characterising which clusters do generate strong lensing features.…”