The prevalence of galaxy overdensities around UV-luminous Lyman

Before the end of epoch reionization, Hydrogen in Universe was predominantly neutral. This leads to a strong attenuation Ly$\alpha$ lines $z\gtrsim6$ galaxies intergalactic medium. Nevertheless, has been detected up very high redshifts ($z\sim9$) for several especially UV luminous galaxies. Here, we test what extent galaxy's local environment might impact transmission such sources. We present an analysis dedicated Hubble Space Telescope (HST) imaging CANDELS/EGS field search fainter neighbours around three most and distant spectroscopically confirmed emitters: EGS-zs8-1, EGS-zs8-2 EGSY-z8p7 at $z_\mathrm{spec}=7.73$, 7.48, 8.68, respectively. combine multi-wavelength HST with Spitzer data reliably select $z\sim7-9$ central, UV-luminous In all cases, find clear enhancement neighbouring compared expected number blank (by factor $\sim 3-9\times$). Our thus reveals ubiquitous overdensities emitting sources heart cosmic reionization epoch. show that our results are excellent agreement expectations from Dragons simulation, confirming theoretical prediction first ionized bubbles preferentially formed overdense regions. JWST follow-up observations identified here will be needed confirm their physical association map out regions produced by these