Les bâtisseurs discrets de l'Univers : JWST et lentille gravitationnelle éclairent le rôle des galaxies naines dans la réionisation ✛

Résumé original

tel que rédigé par les auteurs, en anglais arXiv:2607.01129v1

We leverage the strong gravitational field of Abell S1063 to identify faint, highly magnified galaxies using ultra-deep James Webb Space Telescope (JWST)/NIRCam imaging from the GLIMPSE survey and ancillary Hubble Space Telescope (HST)/ACS imaging from the Hubble Frontier Fields program. We construct a photometric catalogue of lensed high-redshift candidates and use these sources to constrain the faint end of the rest-frame UV luminosity function (UVLF) over $$z\simeq6$$--11. Rather than treating the UVLF turnover ($$M_{\rm t}$$) as a hard cutoff, we model it as a gradual quadratic suppression and explicitly account for the potential continued contribution of galaxies beyond the turnover. In a shallow-turnover scenario, up to one-third of the UV luminosity density can arise from sources fainter than $$M_{\rm t}$$. While we find no direct evidence for a turnover down to $$M_{\rm UV}=-13.5$$ at $$z=6$$, our analysis can only confidently exclude weak, medium, and strong turnover models down to $$M_{\rm t}=-15.9$$, $$-15.1$$, and $$-14.8$$, respectively. Across these models, we infer lower limits of the UV luminosity, star formation density, and the ionization rate as: $$\rho_{\rm UV}\geq22\times10^{25}\,{\rm erg\,s^{-1}\,Hz^{-1}\,Mpc^{-3}}$$, $${\rm SFRD}\geq25\times10^{-3}\,M_\odot\,{\rm yr^{-1}\,Mpc^{-3}}$$, and $$\log_{10}(\dot{n}_{\rm ion}/{\rm s^{-1}\,Mpc^{-3}})\geq51.02$$. We find that galaxies fainter than the conventional $$M_{\rm UV}=-17$$ limit contribute more than half of the UV luminosity density and at least $$\sim64\%$$ of the ionizing photons produced by star-forming galaxies at $$z=6$$. Because our turnover model permits a suppressed, but non-zero, galaxy population beyond $$M_{\rm t}$$, sources fainter than the turnover remain contributors to both $$\rho_{\rm UV}$$ and $$\dot{n}_{\rm ion}$$, emphasizing the need to consider the turnover and its shape during reionization.