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Arxiv: Galaxies Going Bananas: Inferring the 3D Geometry of High-Redshift Galaxies with JWST-CEERS Published: 10/23/2023 9:00:06 PM Updated: 1/15/2024 5:11:49 PM

Paper abstract: The 3D geometry of high-redshift galaxies remains poorly understood. We builda differentiable Bayesian model and use Hamiltonian Monte Carlo to efficientlyand robustly infer the 3D shapes of star-forming galaxies in JWST-CEERSobservations with \log M_*/M_{\odot}=9.0-10.5 at z=0.5-8.0. We reproduceprevious results from HST-CANDELS in a fraction of the computing time andconstrain the mean ellipticity, triaxiality, size and covariances with samplesas small as ~50 galaxies. We find high 3D ellipticities for allmass-redshift bins suggesting oblate (disky) or prolate (elongated) geometries.We break that degeneracy by constraining the mean triaxiality to be ~1 for\log M_*/M_{\odot}=9.0-9.5 dwarfs at z>1 (favoring the prolate scenario),with significantly lower triaxialities for higher masses and lower redshiftsindicating the emergence of disks. The prolate population traces out a``banana'' in the projected b/a-\log a diagram with an excess of low b/a,large \log a galaxies. The dwarf prolate fraction rises from ~25\% atz=0.5-1.0 to ~50-80\% at z=3-8. If these are disks, they cannot beaxisymmetric but instead must be unusually oval (triaxial) unlike localcircular disks. We simultaneously constrain the 3D size-mass relation and itsdependence on 3D geometry. High-probability prolate and oblate candidates showremarkably similar S\'ersic indices (n~1), non-parametric morphologicalproperties and specific star formation rates. Both tend to be visuallyclassified as disks or irregular but edge-on oblate candidates show more dustattenuation. We discuss selection effects, follow-up prospects and theoreticalimplications.