James Webb Space Telescope Feed Post

JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs Published: 8/5/2022 7:56:44 PM Updated: 6/6/2023 12:44:45 AM

Paper abstract: We present an interstellar medium and stellar population analysis of threespectroscopically confirmed z>7 galaxies in the ERO JWST NIRCam and JWSTNIRSpec data of the SMACS J0723.3-7327 cluster. We use the Bayesian spectralenergy distribution (SED) fitting code \texttt{Prospector} with a flexiblestar-formation history (SFH), a variable dust attenuation law, and aself-consistent model of nebular emission (continuum and emission lines).Importantly, we self-consistently fit both the emission line fluxes from JWSTNIRSpec and the broad-band photometry from JWST NIRCam, taking into accountslit-loss effects. We find that these three z=7.6-8.5 galaxies(M_{*}~10^{8}~M_{\odot}) are young with rising SFHs andmass-weighted ages of 3-4 Myr, though we find indications for underlyingolder stellar populations. The inferred gas-phase metallicities broadly agreewith the direct metallicity estimates from the auroral lines. The galaxy withthe lowest gas-phase metallicity (\mathrm{Z}_{\rmgas}=0.06~\mathrm{Z}_{\odot}) has a steeply rising SFH, is very compact(<0.2~\mathrm{kpc}) and has a high star-formation rate surface density(\Sigma_{\rmSFR}~22~\mathrm{M}_{\odot}~\mathrm{yr}^{-1}~\mathrm{kpc}^{-2}),consistent with rapid gas accretion. The two other objects with highergas-phase metallicity show more complex multi-component morphologies on kpcscales, indicating that their recent increase in star-formation rate is drivenby mergers or internal, gravitational instabilities. We discuss effects ofassuming different SFH priors or only fitting the photometric data. Ouranalysis highlights the strength and importance of combining JWST imaging andspectroscopy for fully assessing the nature of galaxies at the earliest epochs.