Methodological refinement of the submillimeter galaxy magnification bias. I. Cosmological analysis with a single redshift bin

Abstract

Aims: The main goal of this work is to test the results of a methodological improvement in the measurement of the magnification bias signal on a sample of submillimeter galaxies. In particular, we investigate the constraining power of cosmological parameters within the ΛCDM model. We also discuss important points that can affect the results.
Methods: We measured the angular cross-correlation function between a sample of foreground GAMA II galaxies in a single wide spectroscopic redshift bin of 0.2 < z < 0.8 and a sample of background submillimeter galaxies from Herschel-ATLAS. We focused on the photometric redshift range of 1.2 < z < 4.0, with an improved methodological framework. Interpreting the weak lensing signal within the halo model formalism and performing a Markov chain Monte Carlo (MCMC) algorithm, we obtained the posterior distribution of both the halo occupation distribution and cosmological parameters within a flat ΛCDM model. Our analysis was also performed with additional galaxy clustering information via a foreground angular auto-correlation function.
Results: We observed an overall remarkable improvement in terms of uncertainties in both the halo occupation distribution and cosmological parameters with respect to previous results. A priori knowledge about β, the logarithmic slope of the background integral number counts, is found to be paramount to derive constraints on σ₈ when using the cross-correlation data alone. Assuming a physically motivated prior distribution for β, we obtain mean values of Ω_m = 0.23_−0.06^+0.03 and σ₈ = 0.79_−0.10^+0.10 and an unconstrained distribution for the Hubble constant. These results are likely to suffer from sampling variance, since one of the fields, G15, appears to have an anomalous behavior with a systematically higher cross-correlation. We find that removing it from the sample yields mean values of Ω_m = 0.27_−0.04^+0.02 and σ₈ = 0.72_−0.04^+0.04 and, for the first time, a (loose) restriction of the Hubble constant is obtained via this observable: h = 0.79_−0.14^+0.13. The addition of the angular auto-correlation of the foreground sample in a joint analysis tightens the constraints, but also reveals a discrepancy between both observables that might be an aggravated consequence of sampling variance or due to the presence of unmodeled aspects on small and intermediate scales.