Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Cosimo Marconcini, Francesco D’Eugenio, Roberto Maiolino, Santiago Arribas, Andrew J. Bunker
| Summary:
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 was
obtained with both the G395H grating (R~ 2700) and the prism (R~ 100). This
target shows a main elongated UV-bright clump and a secondary component
detected in continuum emission at a projected distance of 2 kpc. The R2700 data
trace the ionised-gas morpho-kinematics in between the two components, showing
an elongated emission mainly traced by [O III]5007. We spatially resolve [O
II]3726,3729, [O III]4959,5007, and [O III]4363, which enable us to map the
electron density (ne ~ 1.0 x 103 cm-3), temperature (Te ~ 1.6 x 104 K), and
direct-method gas-phase metallicity (-1.2 to -0.7 dex solar). A spatially
resolved full-spectrum modelling of the prism indicates a north-south gas
metallicity and stellar age gradient between the two components. We found
3-sigma evidence of a spatially resolved anti-correlation of the gas-phase
metallicity and the star formation rate density, which is likely driven by gas
inflows, enhancing the star formation in JD1. We employ high-z sensitive
diagnostic diagrams to rule out the presence of a strong AGN in the main
component. These findings show the unambiguous presence of two distinct stellar
populations, with the majority of the mass ascribed to an old star formation
burst, as suggested by previous works. We disfavour the possibility of a
rotating-disc nature for MACS1149-JD1; we favour a merger event that has led to
a recent burst of star formation in two separate regions, as supported by high
values of [O III]5007/Hbeta, ionised gas velocity dispersion, and gas-phase
metallicity.
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