Resolving stellar populations, star formation, and interstellar medium conditions with JWST in a large spiral galaxy at z ≈ 2

Cosmic noon represents the prime epoch where today’s massive galaxies assembled most of their stellar masses, and it is an ideal period for observations with both the space-based James Webb Telescope (JWST) and ground-based near-IR integral-field unit (IFU) spectrographs. This work analyzes JWST NIRSpec Micro Shutter Array (MSA) and NIRCam Wide Field Slitless Spectroscopy (WFSS) observations of K20-ID7, a large spiral, star-forming (SF) galaxy at z = 2.224 with evidence of radial gas inflows. Leveraging ground-based IFU ERIS observations, we conducted a comprehensive and resolved study of the interstellar medium and stellar properties of this galaxy, covering the rest-frame optical to near-IR. Our analysis – using several emission-line diagnostics, resolved spectral energy distribution (SED) fitting of high-resolution imaging, and Pa β line detection in NIRCam WFSS data – reveals massive SF clumps ( M ★ ≃ (0.67 − 3.5) × 10 9 M ⊙ ) with star formation rates (SFRs) of 3 − 24 M ⊙ yr −1 , low dust attenuation ( A V ≃ 0.4), electron densities ( n e ≲ 300 cm −3 ), and ionization parameter (log( U ) ≃ −3.0). The central bulge is modestly massive ( M ★ = (7 ± 3)×10 9 M ⊙ ), heavily obscured ( A V = 6.43 ± 0.55), and likely formed most of its stellar mass in the past (SFR = 82 ± 42 M ⊙ yr −1 over the last ∼100 Myr). Yet, it continues to form stars at a lower rate (SFR = 12 ± 8 M ⊙ yr −1 over the last ∼10 Myr). We infer a relatively low sulfur abundance of log(S/O) ≃ −1.9, which may have implications for sulfur production via type I supernova explosions. Moreover, all distinct galaxy regions feature a metallicity of 12+log(O/H) ≈ 8.54, likely due – along with the enhanced N/O abundance (i.e., log(N/O) ≃ −1.0) – to dilution effects from radial inflows of metal-poor gas. Lastly, we find tentative evidence of a negative gradient in stellar age, suggesting possible inside-out growth for K20-ID7.