Gravitational lensing modification of the high redshift galaxy luminosity function

TL;DR

This paper investigates how gravitational lensing affects the observed luminosity function of high-redshift galaxies, showing that finite galaxy sizes and lens ellipticity reduce magnification bias and influence size constraints.

Contribution

It introduces a detailed model of magnification bias considering finite source sizes and lens ellipticity, providing new insights into the intrinsic sizes of high-redshift galaxies.

Findings

Finite source sizes and lens ellipticity suppress magnification bias.

The UV luminosity function constrains galaxy sizes, favoring smaller galaxies.

Tabulated maximum magnification as a function of source size and lens ellipticity.

Abstract

The bright end of the rest-frame UV luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing magnification bias. Motivated by recent discoveries of very high-z galaxies with JWST, we study the dependence of magnification bias on the finite size of sources at $6<z<14$. We calculate the magnification probability distributions and use these to calculate the magnification bias assuming a rest-frame Schechter UVLF for galaxies at redshift $6<z<14$. We find that the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end which declines more sharply than the power-law resulting from assumption of point sources. By assuming a luminosity-size relation for the source population and comparing with the observed $z=6$ galaxy luminosity function from Harikane+(2022), we show that the UVLF can be used to set mild constraints on the galaxies intrinsic size, favoring smaller galaxies compared to the fiducial luminosity-size relation. In the future, wide surveys using Euclid and Roman Space Telescope will place stronger constraints. We also tabulate the maximum magnification possible as a function of source size and lens ellipticity.