James Webb Space Telescope Feed Post

Arxiv: Exploring the nature of UV-bright z \gtrsim 10 galaxies detected by JWST: star formation, black hole accretion, or a non-universal IMF? Published: 5/8/2023 9:00:00 PM Updated: 2/12/2024 4:12:17 PM

Paper abstract: We use the Cosmic Archaeology Tool (CAT) semi-analytical model to explore thecontribution of Population (Pop) III/II stars and active galactic nuclei (AGNs)to the galaxy UV luminosity function (LF) evolution at 4 <= z <= 20. Wecompare in particular with recent JWST data in order to explore the apparenttension between observations and theoretical models in the number density ofbright galaxies at z \gtrsim 10. The model predicts a star formation historydominated by UV faint (M_{\rm UV} > - 18) galaxies, with a Pop IIIcontribution of <~ 10\% (<~ 0.5\%) at z ~eq 20 (z ~eq10). Stars are the primary sources of cosmic reionization, with 5 - 10 \% ofionizing photons escaping into the intergalatic medium at 5 <= z <= 10,while the contribution of unobscured AGNs becomes dominant only at z <~5. The predicted stellar and AGN UV LFs reproduce the observational data at 5<~ z <~ 9 - 10. At higher redshift, CAT predicts a steeperevolution in the faint-end slope (M_{\rm UV} > - 18), and a number density ofbright galaxies (M_{\rm UV} ~eq -20) consistent with data at z ~ 10 -11, but smaller by 0.8 dex at z ~ 12 - 13, and 1.2 dex at z ~ 14 -16, when compared to the values estimated by recent studies. Including the AGNemission does not affect the above findings, as AGNs contribute at most to<~ 10 \% of the total UV luminosity at M_{\rm UV} < - 19 and z\gtrsim 10. Interestingly, considering a gradual transition in the stellarIMF, modulated by metallicity and redshift as suggested by recent simulations,the model agrees with JWST data at z ~ 12 - 13, and the disagreement at z~ 14 - 16 is reduced to 0.5 dex.