We report the first gas-phase metallicity map of a distant galaxy measured with the James Webb Space Telescope (JWST). We use the NIRISS slitless spectroscopy acquired by the GLASS Early Release Science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at z = 3.06 behind the A2744 galaxy cluster. This galaxy (dubbed GLASS-Zgrad1) has stellar mass ∼108.6 M ⊙, instantaneous star formation rate ∼8.6 M ⊙ yr−1 (both corrected for lensing magnification), and global metallicity one-fourth solar. From its emission-line maps ([O iii], Hβ, Hγ, [Ne iii], and [O ii]), we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling Bayesian inference method. The exquisite resolution and sensitivity of JWST/NIRISS, combined with lensing magnification, enable us to resolve this z ∼ 3 dwarf galaxy in ≳50 resolution elements with sufficient signal, an analysis hitherto not possible. We find that the radial metallicity gradient of GLASS-Zgrad1 is strongly inverted (i.e., positive): Δ log ( O / H ) / Δ r = 0.165 ± 0.023 dex kpc−1. This measurement is robust at ≳ 4 − σ confidence level against known systematics. This positive gradient may be due to tidal torques induced by a massive nearby (∼15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of GLASS-Zgrad1. These first results showcase the power of JWST wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation (z ≳ 2). Reaching masses ≲ 109 M ⊙ at these redshifts is especially valuable to constrain the effects of galactic feedback and environment and is possible only with JWST’s new capabilities.
|Original language||English (US)|
|Journal||Astrophysical Journal Letters|
|State||Published - Oct 1 2022|
Bibliographical noteFunding Information:
We would like to thank the anonymous referee for careful reading and constructive comments that help improve the clarity of this paper. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program JWST-ERS-1324. We acknowledge financial support from NASA through grant JWST-ERS-1324. X.W. is supported by CAS Project for Young Scientists in Basic Research, Grant No. YSBR-062. X.W. thanks Zach Hemler for kindly providing his compilations of gradient measurements from the literature and Patricia Tissera for providing the tabulated results of the latest EAGLE simulations. K.G. acknowledges support from Australian Research Council Laureate Fellowship FL180100060. M.B. acknowledges support from the Slovenian national research agency ARRS through grant N1-0238.
© 2022. The Author(s). Published by the American Astronomical Society.