Size bias and differential lensing of strongly lensed, dusty galaxies identified in wide-field surveys

TL;DR

This paper investigates how size bias and differential lensing affect the selection and observation of strongly lensed dusty galaxies in wide-field surveys, highlighting the importance of lens modeling for accurate interpretation.

Contribution

It identifies size bias in lensed galaxy samples and models differential lensing effects, emphasizing the need for multi-frequency lens modeling to correct observational biases.

Findings

Higher flux sources are biased towards more compact objects.

At high magnifications, compact regions are more strongly amplified.

At intermediate magnifications (~10), extended regions can be more magnified.

Abstract

We address two selection effects that operate on samples of gravitationally lensed dusty galaxies identified in millimeter- and submillimeter-wavelength surveys. First, we point out the existence of a "size bias" in such samples: due to finite source effects, sources with higher observed fluxes are increasingly biased towards more compact objects. Second, we examine the effect of differential lensing in individual lens systems by modeling each source as a compact core embedded in an extended diffuse halo. Considering the ratio of magnifications in these two components, we find that at high overall magnifications the compact component is amplified by a much larger factor than the diffuse component, but at intermediate magnifications (~10) the probability of a larger magnification for the extended region is higher. Lens models determined from multi-frequency resolved imaging data are crucial to correct for this effect.