Spatially resolved emission lines in galaxies at 4 ≤ z < 10 from the JADES survey: Evidence for enhanced central star formation

¹ University of Ljubljana FMF, Jadranska 19, 1000 Ljubljana, Slovenia
² Dipartimento di Fisica, Università di Trieste, Sezione di Astronomia, Via G. B. Tiepolo 11, I-34131 Trieste, Italy
³ INAF – Osservatorio Astronomico di Trieste, Via G. Tiepolo 11, I-34143 Trieste, Italy
⁴ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34151 Trieste, Italy
⁵ Cavendish Laboratory – Astrophysics Group, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁶ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁷ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁹ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino, Firenze, Italy
¹⁰ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
¹¹ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹² Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹³ Centro de Astrobiología (CAB), CSIC-INTA, Cra. de Ajalvir Km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁴ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
¹⁵ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
¹⁶ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
¹⁷ Department of Astronomy and Astrophysics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA

^⋆ Corresponding author; roberta.tripodi@inaf.it

Received: 14 March 2024
Accepted: 4 November 2024

Abstract

We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at 4 ≤ z < 10 using James Webb Space Telescope (JWST)/NIRSpec Micro Shutter Assembly (MSA) data from the JWST Advanced Deep Extragalactic (JADES) survey, focusing on deep, spatially resolved spectroscopy in the GOODS-S extragalactic field. By performing a stacking of the 2D spectra of the galaxies in our sample, we find an increasing or flat radial trend with increasing radius for [O III]λ5007/Hβ and a decreasing trend for the blended spectral complex (Hη + [Ne III]λ3869 + He Iλ3889 + Hζ)/[O II]λ3727 (3−4σ significance). These results are still valid when stacking the sample in two redshift bins (i.e. 4 ≤ z < 5.5 and 5.5 ≤ z < 10). The comparison with star-formation photoionisation models suggests that the ionisation parameter increases by ∼0.5 dex with redshift. Under the hypothesis that radial variations in (Hη + [Ne III]λ3869 + He Iλ3889 + Hζ)/[O II]λ3727 are dominated by trends in [Ne III]λ3869/[O II]λ3727, we find a tentative metallicity gradient that increases with radius (i.e. ‘inverted’) in both redshift bins. Moreover, our analysis reveals strong negative gradients for the equivalent width of Hβ (7σ significance). This trend persists even after removing known active galactic nucleus candidates, and is therefore consistent with a radial gradient primarily in stellar age and secondarily in metallicity. Taken together, our results suggest that the sample is dominated by active central star formation, with possibly inverted metallicity gradients sustained by recent episodes of accretion of pristine gas or strong radial flows. Deeper observations and larger samples are needed to confirm these preliminary results and to validate our interpretation.