The star-forming and ionizing properties of dwarf z ~ 6-9 galaxies in JADES: Insights on bursty star formation and ionized bubble growth

Endsley, R, Stark, DP, Whitler, L, Topping, MW, Johnson, BD, Robertson, B, Tacchella, S, Alberts, S, Baker, WM, Bhatawdekar, R, Boyett, K, Bunker, AJ, Cameron, AJ, Carniani, S, Charlot, S, Chen, Z, Chevallard, J, Curtis-Lake, E, Danhaive, AL, Egami, E et al (2024) The star-forming and ionizing properties of dwarf z ~ 6-9 galaxies in JADES: Insights on bursty star formation and ionized bubble growth. Monthly Notices of the Royal Astronomical Society, 533 (1). pp. 1111-1142. ISSN 0035-8711

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Abstract

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 JADES (JWST Advanced Deep Extragalactic Survey)/NIRCam (Near-Infrared Camera) imaging to study the star-forming and ionizing properties of 756 z∼ 6 − 9 galaxies, including hundreds of very ultraviolet (UV)-faint objects (MUV > −18). The faintest (m ∼ 30) galaxies in our sample typically have stellar masses of M∗ ∼ (1 − 3) × 107 M⊙ 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⊙) in our sample. We infer a strong (factor >2) decline in the typical [O III]+H β equivalent widths (EWs) towards very faint z ∼ 6 − 9 galaxies, yet a weak UV luminosity dependence on the H α 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. Our data provide evidence that the brightest galaxies are frequently experiencing a recent strong upturn in star formation rate. 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 Ly α emitters. One Ly α emitter lies close to a strong photometric overdensity, while the other shows no significant nearby overdensity, perhaps implying that not all strong z > 7 Ly α emitters reside in large ionized bubbles.

Item Type:	Article
Uncontrolled Keywords:	37 Earth Sciences; 51 Physical Sciences; 3705 Geology; 5109 Space Sciences; 5107 Particle and High Energy Physics; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	29 July 2024
Date of first compliant Open Access:	2 March 2026
Date Deposited:	02 Mar 2026 09:45
Last Modified:	02 Mar 2026 09:45
DOI or ID number:	10.1093/mnras/stae1857
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28152

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