Cosmology through arc statistics I: sensitivity to Ω_mand σ₈

Abstract

The next generation of large sky photometric surveys will finally be able to use arc statistics as a cosmological probe. Here we present the first of a series of papers on this topic. In particular, we study how arc counts are sensitive to the variation of two cosmological parameters: the (total) matter density parameter, Ω m , and the normalisation of the primordial power spectrum, expressed in terms of σ 8 . Both these parameters influence the abundances of collapsed structures and their internal structure. We compute the expected number of gravitational arcs with various length-to-width ratios in mock light cones, by varying these cosmological parameters in the ranges 0.1 Ω m 0.5 and 0.6 σ 8 1. We find that the arc counts dependence on Ω m and σ 8 is similar, but not identical, to that of the halo counts. We investigate how the precision of the constraints on the cosmological parameters based on arc counts depends on the survey area. We find that the constraining power of arc statistics degrades critically only for surveys covering an area smaller than 10% of the whole sky. Finally, we consider the case in which the search for arcs is done only in frames where galaxy clusters have been previously identified. Adopting the selection function for galaxy clusters expected to be detected from photometric data in future wide surveys, we find that less than 10% of the arcs will be missed, with only a small degradation of the corresponding cosmological constraints.

The universality of the virial halo mass function and models for non-universality of other halo definitions

“…For an extensive review, see Borgani & Kravtsov (2011). However in the near future, many wide-field surveys are expected to use the cluster mass function to constrain cosmological parameters (Pillepich et al 2012;Laureijs et al 2011;Sartoris et al 2015;Boldrin et al 2015). In the light of these, a mass function calibrated to an accuracy of a few percent, and flexible enough to account for different halo identification definitions, is of primary importance.…”

Strong-lensing of Gravitational Waves by Galaxy Clusters

“…Therefore R detect will grow as more strong-lensing clusters are discovered. Forecasts for upcoming large-scale optical/near-infrared surveys indicate that Euclid and LSST will find of order 1 strong-lensing cluster per square degree in the redshift range z ∼ 0.2 − 0.5 considered above (Boldrin et al, 2016). It should therefore be possible to achieve a further two orders of magnitude gain to give R detect 1 per detector year during the 2020s.…”

Simulation-based marginal likelihood for cluster strong lensing cosmology

“…For clusters of a fixed mass at the time of observation, lower values of Ω M , Ω Λ or σ 8 or higher values of the spectral index, n, would require the host haloes to have formed earlier, and subsequently lead to higher concen-⋆ E-mail: madhura.killedar.astro@gmail.com (MK) trations (Cole & Lacey 1996;Tormen et al 1997;Navarro et al 1997;Wechsler et al 2002;van den Bosch 2002). Galaxy clusters gravitationally lens and distort the images of background galaxies; their lensing efficiency is a powerful probe of cosmology with the ability to constrain the aforementioned structure formation parameters (Bartelmann et al 1998;Takahashi & Chiba 2001;Bartelmann et al 2003;Wambsganss et al 2004;Boldrin et al 2016). This is partly because the cosmological model determines the formation history of clusters, but also because the critical surface mass density for lensing, a function of the angular diameter distances between observer, lens and source(s), is also dependent on these cosmological parameters.…”