The Gas and Stellar Content of a Metal-poor Galaxy at z = 8.496 as Revealed by JWST and ALMA
Schaerer, D.; Magdis, G. E.; Bauer, F. E.; Brammer, G.; Fujimoto, S.; Watson, D.; Kokorev, V.; Greve, T. R.; Toft, S.; Valentino, F.; Rizzo, F.; Giménez-Arteaga, C.; Kohno, K.; Espada, D.; Koekemoer, A. M.; van der Wel, A.; Nelson, E. J.; Knudsen, K. K.; Shapley, A. E.; Heintz, K. E.; González-López, J.; Gillman, S.; Lee, M. M.; Vijayan, A. P.; Hatsukade, B.; Sanders, R. L.; Harikane, Y.; Strait, V. B.; Christiansen, C. R.; Wilson, S. N.
Denmark, United States, Spain, Chile, Japan, Sweden, Netherlands, Switzerland, France, Germany, Belgium
Abstract
We present a joint analysis of the galaxy S04590 at z = 8.496 based on NIRSpec, NIRCam, and NIRISS observations obtained as part of the Early Release Observations program of the James Webb Space Telescope (JWST) and the far-infrared [C II] 158 μm emission line detected by dedicated Atacama Large Millimeter/submillimeter Array (ALMA) observations. We determine the physical properties of S04590 from modeling of the spectral energy distribution (SED) and through the redshifted optical nebular emission lines detected with JWST/NIRSpec. The best-fit SED model reveals a low-mass (M ⋆ = 107.2-108 M ⊙) galaxy with a low oxygen abundance of $12+\mathrm{log}({\rm{O}}/{\rm{H}})={7.16}_{-0.12}^{+0.10}$ derived from the strong nebular and auroral emission lines. Assuming that [C II] effectively traces the interstellar medium, we estimate the total gas mass of the galaxy to be M gas = (8.0 ± 4.0) × 108 M ⊙ based on the luminosity and spatial extent of [C II]. This yields an exceptionally high gas fraction, f gas = M gas/(M gas + M ⋆) ≳ 90%, though one still consistent with the range expected for low metallicity. We further derive the metal mass of the galaxy based on the gas mass and gas-phase metallicity, which we find to be consistent with the expected metal production from Type II supernovae. Finally, we make the first constraints on the dust-to-gas (DTG) and dust-to-metal (DTM) ratios of galaxies in the epoch of reionization at z ≳ 6, showing overall low mass ratios of logDTG < -3.8 and logDTM < -0.5, though they are consistent with established scaling relations and in particular with those of the local metal-poor galaxy I Zwicky 18. Our analysis highlights the synergy between ALMA and JWST in characterizing the gas, metal, and stellar content of the first generation of galaxies.