Evidence for the Faint-End Suppression in the z = 6 $\sim$ 8 UV Luminosity Function: A Lensing Analysis of Abell 2744

Abstract

We determine the $z=6-8$ ultraviolet (UV) LF in the JWST UNCOVER field behind Abell 2744, through a depth-tied completeness model and source-plane selection taking multiple images into account. We compute the intrinsic $M_{UV}$ LFs and lens-dependent effective volumes $V_{eff,\ell}(M_{UV})$ for two of them (CATS, GLAFIC), and construct binned LFs with statistical (Gehrels) errors presented separately from the lens-model spread. When fitting each lens model independently with both the original and turnover-extended form (while keeping $M^*=-20.5$), we obtain decisive model selection in favour of a faint-end turnover. The peak of the turnover posteriors is at $\alpha \simeq -1$, $\beta \simeq 1.6$, and drive $M_T$ to the high side of our prior ($\sim -18$) and the difference in normalization between CATS-GLAFIC is absorbed into $\phi^*$. A similar magnification-bias test in the image plane gives a $B(\mu)$ trend matching to what is expected, which provides an internal consistency of our selection and volumes. Our results indicate an early suppression of the UV LF at $z=6-8$, and carry implications for the ionizing contribution of ultra-faint systems during reionization.