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Arxiv: Mapping reionization bubbles in the JWST era I: empirical edge detection with Lyman alpha emission from galaxies Published: 11/6/2024 9:00:01 PM Updated: 11/6/2024 9:00:01 PM

Paper abstract: Ionized bubble sizes during reionization trace physical properties of thefirst galaxies. JWST's ability to spectroscopically confirm and measureLyman-alpha (Ly\alpha) emission in sub-L* galaxies opens the door to mappingionized bubbles in 3D. However, existing Lya-based bubble measurementstrategies rely on constraints from single galaxies, which are limited by thelarge variability in intrinsic Ly\alpha emission. As a first step, we presenttwo bubble size estimation methods using Lya spectroscopy of ensembles ofgalaxies, enabling us to map ionized structures and marginalize over Ly\alphaemission variability. We test our methods using Gpc-scale reionizationsimulations of the intergalactic medium (IGM). To map bubbles in the plane ofthe sky, we develop an edge detection method based on the asymmetry ofLy\alpha transmission as a function of spatial position. To map bubbles alongthe line-of-sight, we develop an algorithm using the tight relation betweenLy\alpha transmission and the line-of-sight distance from galaxies to thenearest neutral IGM patch. Both methods can robustly recover bubbles withradius \gtrsim10 comoving Mpc, sufficient for mapping bubbles even in theearly phases of reionization, when the IGM is ~70-90\% neutral. Thesemethods require \gtrsim0.002-0.004 galaxies/cMpc^3, a 5\sigma Ly\alphaequivalent width upper limit of <~30\r{A} for the faintest targets, andredshift precision \Delta z <~ 0.015, feasible with JWST spectroscopy.Shallower observations will provide robust lower limits on bubble sizes.Additional constraints on IGM transmission from Ly\alpha escape fractions andline profiles will further refine these methods, paving the way to our firstdirect understanding of ionized bubble growth.