Anatomy of a z=6 Lyman-{α} emitter down to parsec scales: extreme UV slopes, metal-poor regions and possibly leaking star clusters

We present a detailed JWST/NIRSpec and NIRCam analysis of a gravitationally-lensed galaxy (μ=17-21) at redshift 6.14 magnified by the Hubble Frontier Field galaxy cluster MACS J0416. The target galaxy is overall a typical compact and UV-faint (MUV=-17.8) Lyman-α emitter, yet the large magnification allows the detailed characterization of structures on sub-galactic scales (down to a few parsecs). Prominent optical Hα, Hβ and [OIII]λλ4959,5007 lines are spatially resolved with the high spectral resolution grating (G395H, R~2700), with large equivalent widths, EW(Hβ+[OIII])1000 , and elevated ionising photon production efficiencies log(ξᵢₒₙ/erg⁻¹Hz)=25.2-25.7. NIRCam deep imaging reveals the presence of compact rest-UV bright regions along with individual star clusters of Reff=3-8~pc in size and M~2·10⁵-5·10⁶~M_ in mass. These clusters are characterised by steep UV slopes, βUV-2.5, which in some cases are associated with a dearth of line emission, indicating possible leaking of the ionizing radiation, as also supported by a Lyman-α emission peaking at ~100~km~s⁻¹ from the systemic redshift. While the entire system is characterised by low-metallicity, ~0.1~Z_, the NIRSpec-IFU map also reveals the presence of a low-luminosity, metal-poor region with Z2%~Z_, barely detected in NIRCam imaging; this region is displaced by >200~pc from one of the brightest structures of the system in UV, and would have been too faint to detect if not for the large magnification of the system.