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

Le résumé fourni par la source

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.

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