Effects of Strong Gravitational Lensing on Millimeter-Wave Galaxy Number Counts

TL;DR

This paper investigates how strong gravitational lensing influences millimeter-wave galaxy counts, using simulations and models to predict counts and redshift distributions, and compares these with recent SPT observations.

Contribution

It introduces a detailed simulation framework accounting for source size and lens ellipticity to predict lensed galaxy counts and redshifts, aligning with recent observational data.

Findings

SPT sources are mostly strongly lensed galaxies at z>2

Predicted counts agree with SPT measurements within uncertainties

Magnification factors depend on source counts and flux assumptions

Abstract

We study the effects of strong lensing on the observed number counts of mm sources using a ray tracing simulation and two number count models of unlensed sources. We employ a quantitative treatment of maximum attainable magnification factor depending on the physical size of the sources, also accounting for effects of lens halo ellipticity. We calculate predicted number counts and redshift distributions of mm galaxies including the effects of strong lensing and compare with the recent source count measurements of the South Pole Telescope (SPT). The predictions have large uncertainties, especially the details of the mass distribution in lens galaxies and the finite extent of sources, but the SPT observations are in good agreement with predictions. The sources detected by SPT are predicted to largely consist of strongly lensed galaxies at z>2. The typical magnifications of these sources strongly depends on both the assumed unlensed source counts and the flux of the observed sources.