Cosmology with the submillimetre galaxies magnification bias: Proof of concept

¹ Departamento de Fisica, Universidad de Oviedo, C. Federico Garcia Lorca 18, 33007 Oviedo, Spain
e-mail: bonaveralaura@uniovi.es
² Instituto Universitario de Ciencias y Tecnologias Espaciales de Asturias (ICTEA), C. Independencia 13, 33004 Oviedo, Spain
³ International School for Advanced Studies (SISSA), Via Bonomea 265, 34136 Trieste, Italy
⁴ INFN Sezione di Trieste, Via Valerio 2, 34127 Trieste, Italy
⁵ Institute for Fundamental Physics of the Universe (IFPU), Via Beirut 2, 34014 Trieste, Italy
⁶ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 1, Roma, Italy
⁷ INFN, Sezione di Roma 2, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 1, Roma, Italy
⁸ School of Physics & Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK

Received: 30 March 2020
Accepted: 2 June 2020

Abstract

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 (M_min, M₁, and α), but also some of the cosmological ones (Ω_m, 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 0.2 < z < 0.8 and a background sample of H-ATLAS galaxies with photometric redshifts > 1.2 is modelled using the traditional halo model description that depends on HOD and cosmological parameters. These parameters are then estimated by performing 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, Ω_m and H₀ cannot be well constrained. However, we can set a lower limit of > 0.24 at 95% confidence level (CL) on Ω_m and we see a slight trend towards H₀ >  70 values. For our constraints on σ₈ we obtain only a tentative peak around 0.75, but an interesting upper limit of σ₈ ≲ 1 at 95% CL. We also study the possibility to derive better constraints by imposing more restrictive priors on the astrophysical parameters.