Strong lensing of submillimetre galaxies: A tracer of foreground structure?

TL;DR

This paper investigates the likelihood of strong gravitational lensing in bright submillimetre galaxies using simulations, revealing most high-redshift sources above 100mJy are strongly lensed, impacting future observational strategies.

Contribution

It provides the first detailed estimates of strong lensing probabilities for SMGs based on the latest simulations and observed distributions, highlighting the role of lensing in high-redshift galaxy detection.

Findings

Almost all high-redshift SMGs above 100mJy are strongly lensed.

Lensing probability increases with observed flux density.

Uncertainty mainly due to unknown SMG spatial extent.

Abstract

The steep source counts and negative K-corrections of bright submillimetre galaxies (SMGs) suggest that a significant fraction of those observed at high flux densities may be gravitationally lensed, and that the lensing objects may often lie at redshifts above 1, where clusters of galaxies are difficult to detect through other means. In this case follow-up of bright SMGs may be used to identify dense structures along the line of sight. Here we investigate the probability for SMGs to experience strong lensing, using the latest N-body simulations and observed source flux and redshift distributions. We find that almost all high redshift sources with a flux density above 100mJy will be lensed, if they are not relatively local galaxies. We also give estimates of the fraction of sources experiencing strong lensing as a function of observed flux density. This has implications for planning follow-up observations for bright SMGs discovered in future surveys with SCUBA-2 and other instruments. The largest uncertainty in these calculations is the maximum allowed lensing amplification, which is dominated by the presently unknown spatial extent of SMGs.