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Arxiv: Preliminary Evidence for Lensing-Induced Alignments of High-Redshift Galaxies in JWST-CEERS Published: 7/24/2024 9:00:01 PM Updated: 7/24/2024 9:00:01 PM

Paper abstract: The majority of low-mass (\log_{10} M_*/M_{\odot}=9-10) galaxies at highredshift (z>1) appear elongated in projection. We use JWST-CEERS observationsto explore the role of gravitational lensing in this puzzle. The typicalgalaxy-galaxy lensing shear \gamma~1\% is too low to explain thepredominance of elongated early galaxies with ellipticity e~0.6.However, non-parametric quantile regression with Bayesian Additive RegressionTrees reveals hints of an excess of tangentially-aligned source-lens pairs with\gamma>10\%. On larger scales, we also find evidence for weak lensing shear.We rule out the null hypothesis of randomly oriented galaxies at \gtrsim99\%significance in multiple NIRCam chips, modules and pointings. The number ofsuch regions is small and attributable to chance, but coherent alignmentpatterns suggest otherwise. On the chip scale, the average complex ellipticity\langle e\rangle~10\% is non-negligible and beyond the level of our PSFuncertainties. The shear variance\langle\overline{\gamma}^2\rangle~10^{-3} is an order of magnitude abovethe conventional weak lensing regime but is more sensitive to PSF systematics,intrinsic alignments, cosmic variance and other biases. Taking it as an upperlimit, the maximum implied ``cosmic shear'' is only a few percent and cannotexplain the elongated shapes of early galaxies. The alignments themselves mayarise from lensing by a protocluster or filament at z~0.75 where we findan overabundance of massive lens galaxies. We recommend a weak lensing searchfor overdensities in ``blank'' deep fields with JWST and the Roman SpaceTelescope.