Insight from JWST/Near Infrared Camera into galaxy overdensities around bright Lyman-alpha emitters during reionization: implications for ionized bubbles at z ∼ 9

Several studies have detected Lyman-alpha (Ly Alpha) from bright (M-UV less than or similar to-21.5) galaxies during the early stages of reionization despite the significantly neutral intergalactic medium. To explain these detections, it has been suggested that z > 7 Ly Alpha emitters (LAEs) inhabit physical Mpc (pMpc)-scale ionized regions powered by overdensities of faint galaxies; however, systematic searches for these overdensities near LAEs have been challenging. Here, we use Cosmic Evolution Early Release Science JWST/Near Infrared Camera imaging to search for large-scale galaxy overdensities near two very ultraviolet (UV)-bright, z = 8.7 LAEs in the Extended Groth Strip (EGS) field. We colour select 27 z = 8.4-9.1 candidates, including the one LAE in the footprint (EGSY8p7). From spectral energy distribution models, we infer moderately faint UV luminosities (-21.2 less than or similar to M-UV less than or similar to-19.1) and stellar masses of M-* approximate to 10(7.5-8.8) M-circle dot. All are efficient ionizing agents (epsilon ion & lowast;approximate to 1025.5-26.0 Hz erg(-1)) and are generally morphologically simple with only one compact (r(e) less than or similar to 140 to similar to 650 pc) star-forming component. 13 candidates lie within 5 arcmin of EGSY8p7, leading to a factor-of-four galaxy overdensity at less than or similar to 5 arcmin (similar to 1.4 projected pMpc at z similar to 8.7) separations from EGSY8p7. Separations of 10-15 arcmin (similar to 2.7-4.1 projected pMpc) are consistent with an average field. The spatial distribution of our sample may qualitatively suggest an R >= 2 pMpc ionized bubble encompassing both LAEs in EGS, which is theoretically unexpected but may be possible for a galaxy population four times more numerous than the average to create with moderate escape fractions (f(esc) greater than or similar to 0.15) over long times (greater than or similar to 200 Myr). Upcoming spectroscopic follow-up will characterize the size of any ionized bubble that may exist and the properties of the galaxies powering such a bubble.