Early Results from GLASS-JWST. IV. Spatially Resolved Metallicity in a Low-mass z ∼ 3 Galaxy with NIRISS*

Abstract

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.

The Identification of a Dusty Multiarm Spiral Galaxy at z = 3.06 with JWST and ALMA

“…We note that there are two companion galaxies in the same field that could be related to A2744-DSG-z3. The first one is a star-forming dwarf galaxy close to A2744-DSG-z3, denoted as GLASS-Z grad1 (Wang et al 2022). The angular offset is ≈3 1 on the image plane and then is delensed to ≈2″.…”

“…Thanks to the JWST/NIRISS grism observations, the target close to A2744-DSG-z3 (GLASS-Zgrad1, recently reported in Wang et al 2022) is identified as one companion galaxy at the same redshift. The stellar mass of GLASS-Zgrad1 is ≈10 9 M e , and the delensed angular separation between the two sources is ≈2″, corresponding to 15.4 kpc at z = 3.06.…”

“…This relation was constructed and calibrated using simulated SEDs derived from stellar population synthesis methods (see Sun et al 2022). Meanwhile, the target GLASS-Z grad1, reported in Wang et al (2022), is a star-forming galaxy with stellar mass (M * ) of ∼10 9 M e at the same redshift. The impact parameter between these two galaxies is ≈3 1.…”

Early Results from GLASS-JWST. VI. Extreme Rest-optical Equivalent Widths Detected in NIRISS Wide Field Slitless Spectroscopy

“…We refer the reader to Roberts-Borsani et al (2022, Paper I of this series) and Vanzella et al (2022, Paper VII of this series) for GLASS-ERS studies that provide detailed discussion and utilization of gravitational lensing. In this study we only measure integrated line properties of galaxies and we refer the reader to Wang et al (2022, Paper IV of this series) for a GLASS-ERS study of spatially resolved emission line properties. Where applicable, we use H 0 = 70 km s −1 Mpc −1 , Ω m = 0.3, and Ω ∧ = 0.7.…”

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

“…We constrain jointly three key ISM properties: gas-phase metallicity (12+log(O/H)), nebular dust extinction (A N V ), and de-reddened Hβ flux ( f Hβ ), through the following likelihood function following Refs. 60,61 , i.e., L ∝ exp…”