Kavli Affiliate: Michael Gladders
| Summary:
We present NIRSpec/IFS observations of a rest-frame UV-bright, massive ($M_* sim 10^10$ M$_odot$, $z_AB=20.5$) galaxy highly magnified by gravitational-lensing observed just after the end of the epoch of reionization ($z=5.04$, $barμsim90$). With JWST accessing the restframe UV and optical spectrum of this galaxy with high fidelity, we classify this UV-bright galaxy as post-starburst in nature — due to weak/absent emission lines and strong absorption features — making this an example of a new class of UV-bright but significantly quenched galaxies being discovered in this epoch. With a median $E(B-V)=0.44pm0.14$, we identify the presence of stellar absorption across the arc both in Balmer lines and the MgII doublet, indicative of older stellar populations dominated by A stars (and potentially B stars). Using spatially-resolved maps of rest-optical strong emission lines, we find a heterogeneous distribution of nebular metallicities across the arc, potentially hinting at different enrichment processes. With a low median lensing-corrected H$α$ star formation rate of SFR$_Hα = 0.024 pm 0.001$ M$_odot$ yr$^-1$, we find in the most "star-forming" clumps indications of lower ionization (log$_10$U $sim -3.2$), lower nebular metallicities (12+log$_10$O/H $lesssim$ 8.3), and hints of higher densities that suggest a possible recent infall of more pristine (low metallicity) gas onto the galaxy. Investigating the regions with no detectable H$β$ emission, we find (for the first time at $z>5$) signatures of diffuse ionized gas (DIG). Separating DIG from HII regions within a galaxy has predominantly been demonstrated at lower redshifts, where such spatial resolution allows clear separation of such regions — highlighting the immense power of gravitational lensing to enable studies at the smallest spatial scales at cosmic dawn.
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