James Webb Space Telescope Feed Post

Arxiv: GA-NIFS: the interplay between merger, star formation and chemical enrichment in MACS1149-JD1 at z=9.11 with JWST/NIRSpec Published: 7/11/2024 6:53:22 PM Updated: 7/11/2024 6:53:22 PM

Paper abstract: We present JWST/NIRSpec integral-field spectroscopy observations of the z ~9.11 lensed galaxy MACS1149-JD1, as part of the GA-NIFS programme. The data wasobtained with both the G395H grating (R~ 2700) and the prism (R~ 100). Thistarget shows a main elongated UV-bright clump and a secondary componentdetected in continuum emission at a projected distance of 2 kpc. The R2700 datatrace the ionised-gas morpho-kinematics in between the two components, showingan elongated emission mainly traced by [O III]5007. We spatially resolve [OII]3726,3729, [O III]4959,5007, and [O III]4363, which enable us to map theelectron density (ne ~ 1.0 x 103 cm-3), temperature (Te ~ 1.6 x 104 K), anddirect-method gas-phase metallicity (-1.2 to -0.7 dex solar). A spatiallyresolved full-spectrum modelling of the prism indicates a north-south gasmetallicity and stellar age gradient between the two components. We found3-sigma evidence of a spatially resolved anti-correlation of the gas-phasemetallicity and the star formation rate density, which is likely driven by gasinflows, enhancing the star formation in JD1. We employ high-z sensitivediagnostic diagrams to rule out the presence of a strong AGN in the maincomponent. These findings show the unambiguous presence of two distinct stellarpopulations, with the majority of the mass ascribed to an old star formationburst, as suggested by previous works. We disfavour the possibility of arotating-disc nature for MACS1149-JD1; we favour a merger event that has led toa recent burst of star formation in two separate regions, as supported by highvalues of [O III]5007/Hbeta, ionised gas velocity dispersion, and gas-phasemetallicity.