2023/06/08 by Ryan Endsley, Daniel P. Stark, Endsley, Ryan +76 · 15 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2306.05295
openalex publication_date 2023/06/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
Reionization is thought to be driven by faint star-forming galaxies, but characterizing this population has long remained very challenging. Here we utilize deep nine-band NIRCam imaging from JADES to study the star-forming and ionizing properties of 756 z∼6-9 galaxies, including hundreds of very UV-faint objects (MUV>-18). The faintest (m∼30) galaxies in our sample typically have stellar masses of M_∗∼(1-3)×107 M_\odot and young light-weighted ages (∼50 Myr), though some show strong Balmer breaks implying much older ages (∼500 Myr). We find no evidence for extremely massive galaxies (>3×1010 M_\odot). We infer a strong (factor >2) decline in the typical [OIII]+Hβ EWs towards very faint z∼6-9 galaxies, yet a weak UV luminosity dependence on the Hα EWs at z∼6. We demonstrate that these EW trends can be explained if fainter galaxies have systematically lower metallicities as well as more recently-declining star formation histories relative to the most UV-luminous galaxies in our sample. Our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in SFR. We also discuss how the EW trends may be influenced by a strong correlation between MUV and Lyman continuum escape fraction. This alternative explanation has dramatically different implications for the contribution of galaxies along the luminosity function to cosmic reionization. Finally, we quantify the photometric overdensities around two z>7 strong Lyα emitters. One Lyα emitter lies close to a strong photometric overdensity while the other shows no significant nearby overdensity, perhaps implying that not all strong z>7 Lyα emitters reside in large ionized bubbles.