Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Mirko Curti, Mirko Curti, , ,
| Summary:
We present the analysis of the stellar and interstellar medium (ISM)
properties of MARTA-4327, a star-forming galaxy at z=2.224 observed by means of
deep JWST/NIRSpec spectroscopy in both medium- and high-resolution gratings as
part of the "Measuring Abundances at high Redshift with the Te Approach"
(MARTA) programme. We report one of the highest-redshift detections of the
Wolf-Rayet (WR) blue and red bumps in a non-lensed system. The broad He
ii$lambda$4686 feature is consistent with a young ($sim 5-6$ Myr) burst
dominated by WN stars, although both SSP models and empirical templates
struggle to reproduce the nitrogen stellar features at $approx$ 4640 A.
Based on the relative strength of the available optical stellar features, we
disfavor the presence of very massive stars (VMS) in this system. Elemental
abundance ratios such as Ne/O, N/O, and Ar/O align with observations of local
star-forming galaxies (including WR galaxies), suggesting that any impact of
the WR population on the chemical enrichment of the ISM is strongly localized.
However, the gas-phase Fe/O ratio appears enhanced compared to local galaxies
of similar metallicity, which we interpret as evidence for reduced Fe depletion
onto dust grains, possibly linked to localized destruction in WR-driven wind
environments. In addition, we detect a broad and blueshifted (~70 km/s)
H$alpha$ component, revealing the presence of an ionized outflow with a mass
loading factor $eta sim 0.2$. Finally, we report the robust detection of O
I$lambda$8446 emission (among the first at high redshift), which we
interpret as originating from Ly$beta$ fluorescence and/or collisional
excitation in dense clumps. Overall, MARTA-4327 represents a unique system for
studying the role of massive stars in shaping the ISM in galaxies at Cosmic
Noon.
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