Early Results from GLASS-JWST. IV. Spatially Resolved Metallicity in a Low-mass z ∼ 3 Galaxy with NIRISS*
Xin Wang, Tucker Jones, Benedetta Vulcani, Tommaso Treu, Takahiro Morishita, Guido Roberts-Borsani, Matthew A. Malkan, Alaina Henry, Gabriel Brammer, Victoria Strait, Maruša Bradač, Kristan Boyett, Antonello Calabrò, M. Castellano, A. Fontana, Karl Glazebrook, Patrick L. Kelly, Nicha Leethochawalit, Danilo Marchesini, P. Santini, Michele Trenti, Lilan Yang
Abstract
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 ∼10 8.6 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 ], H β , H γ , [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): <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>r</mml:mi> </mml:math> = 0.165 ± 0.023 dex kpc −1 . This measurement is robust at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>≳</mml:mo> <mml:mn>4</mml:mn> <mml:mo>−</mml:mo> <mml:mspace width="0.25em"/> <mml:mi>σ</mml:mi> </mml:math> 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 ≲ 10 9 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.