Biases in physical parameter estimates through differential lensing magnification

TL;DR

This paper investigates how differential lensing magnification biases the estimation of physical properties of background galaxies, emphasizing the need for detailed lens modeling to correct these biases.

Contribution

It introduces a simplified galaxy model to analyze the impact of differential magnification on spectral properties and highlights the importance of accurate lens modeling.

Findings

Differential magnification alters derived galaxy properties.

Biases can lead to over- or under-estimates of parameters.

Strong lensing regions cause significant biases.

Abstract

We study the lensing magnification effect on background galaxies. Differential magnification due to different magnifications of different source regions of a galaxy will change the lensed composite spectra. The derived properties of the background galaxies are therefore biased. For simplicity, we model galaxies as a superposition of an axis-symmetric bulge and a face-on disk in order to study the differential magnification effect on the composite spectra. We find that some properties derived from the spectra (e.g., velocity dispersion, star formation rate and metallicity) are modified. Depending on the relative positions of the source and the lens, the inferred results can be either over- or under-estimates of the true values. In general, for an extended source at strong lensing regions with high magnifications, the inferred physical parameters (e.g. metallicity) can be strongly biased. Therefore detailed lens modelling is necessary to obtain the true properties of the lensed galaxies.