The Strongly Lensed H α -emitting Galaxy Population at 3.8 < z < 6.6

Abstract H α luminosity traces the ionizing-photon output of short-lived, massive stars and is therefore a key diagnostic of star formation in high-redshift galaxies. Recent JWST observations have delivered updated H α luminosity functions (LFs) of H α -emitting galaxies out to an unprecedented 3.8 < z < 6.6, yet strong gravitational lensing can systematically skew the bright end and bias the cosmic star formation rate (SFR) density inferred from the LF. To quantify the population of strongly lensed H α -emitting galaxies at 3.8 < z < 6.6, we use Monte Carlo sampling based on these new LFs and gravitational-lensing ray-tracing simulations with lenstronomy : sources adopt Sérsic surface-brightness profiles; foreground deflectors are drawn from an empirical velocity-dispersion function to build a 900 deg 2 light cone. In parallel, we convolve the intrinsic LF with the global magnification probability density to obtain an analytic approximation of lensed counts, which efficiently propagates intrinsic LF parameter uncertainties to lensed results. Our simulations show that ≳90% of H α -emitting galaxies with SFR ≳ 10 3 M ⊙ yr −1 are strongly lensed systems at 3.8 < z < 6.6, and the lensed number fraction per SFR bin rises from ∼10% to ∼90% across log 10 SFR ≃ 2.64 –3.05 M ⊙ yr −1 . Given the ∼ 62 arcmin 2 GOODS-South coverage and a 50%–100% overall completeness, the existing FRESCO and CONGRESS observations should contain ∼1.7–3.4 strongly lensed H α -emitting galaxies with SFR > 10 M ⊙ yr −1 . These results imply that, in the JWST era, analyses relying on samples with apparent SFR ≳ 10 3 M ⊙ yr −1 must correct for strong lensing in order to obtain unbiased inferences.