Cosmology with the submillimetre galaxies magnification bias: Proof of concept

Context. As recently demonstrated, high-z submillimetre galaxies (SMGs) are the perfect background sample for tracing the mass density profiles of galaxies and clusters (baryonic and dark matter) and their time-evolution through gravitational lensing. Their magnification bias, a weak gravitational lensing effect, is a powerful tool for constraining the free parameters of a halo occupation distribution (HOD) model and potentially also some of the main cosmological parameters. Aims. The aim of this work is to test the capability of the magnification bias produced on high-z SMGs as a cosmological probe. We exploit cross-correlation data to constrain not only astrophysical parameters (Mmin, M1, and α), but also some of the cosmological ones (Ωm, σ8, and H0) for this proof of concept. Methods. The measured cross-correlation function between a foreground sample of GAMA galaxies with spectroscopic redshifts in the range 0.21.2 is modelled using the traditionalhalomodeldescriptionthatdependsonHODandcosmologicalparameters.Theseparametersarethenestimatedbyperforming a Markov chain Monte Carlo analysis using different sets of priors to test the robustness of the results and to study the performance of this novel observable with the current set of data. Results. With our current results, Ωm and H0 cannot be well constrained. However, we can set a lower limit of >0.24 at 95% confidence level (CL) on Ωm and we see a slight trend towards H0 > 70 values. For our constraints on σ8 we obtain only a tentative peak around0.75,butaninterestingupperlimitof σ8 . 1at95%CL.Wealsostudythepossibilitytoderivebetterconstraintsbyimposing more restrictive priors on the astrophysical parameters. Key words. galaxies: high-redshift – submillimeter: galaxies – gravitational lensing: weak – cosmological parameters.