Metal-Enriched Neutral Gas Reservoir around a Strongly-lensed, Low-mass Galaxy at z=4 Identified by JWST/NIRISS and VLT/MUSE

Xiaojing Lin, Zheng Cai, Siwei Zou, Zihao Li, Zuyi Chen, Fuyan Bian, Fengwu Sun, Yiping Shu, Yunjing Wu, Mingyu Li, Jianan Li, Xiaohui Fan, J. Xavier Prochaska, Daniel Schaerer, Stephane Charlot, Daniel Espada, Miroslava Dessauges-Zavadsky, Eiichi Egami, Daniel Stark, Kirsten K. Knudsen, Gustavo Bruzual, Jacopo Chevallard

Submitted on 7 September 2022


Direct observations of low-mass, low-metallicity galaxies at z4 provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in sources similar to those that reionized the Universe. Combining the James Webb Space Telescope (JWST), VLT/MUSE, and ALMA, we present detailed observations of a strongly lensed, low-mass (107.6 M) galaxy at z=3.98 (also see Vanzella et al. 2022). We identify strong narrow nebular emission, including CIV λλ1548,1550, HeII λ1640, OIII] λλ1661,1666, [NeIII] λ3868, [OII] λ3727, and Balmer series of Hydrogen from this galaxy, indicating a metal-poor HII region (0.12 Z) powered by massive stars. Further, we detect a metal-enriched damped Lyα system (DLA) associated with the galaxy with the HI column density of NHI1021.8 cm2. The metallicity of the associated DLA may reach the super solar metallicity (Z). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope (β) map at the spatial resolution of 100 pc at z=4, with steep UV slopes reaching β2.5 around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further support that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low column-density neutral gas.


Comment: 4 pages, 1 table; submitted to the ApJL; welcome comments

Subject: Astrophysics - Astrophysics of Galaxies