AI Insight
This study uses JWST observations to analyze how galaxies at redshifts z=5-12 acquired their stellar mass through a semi-empirical model based on observed UV luminosity functions. The research finds that massive galaxies experienced bursty star formation with exceptionally high star formation efficiencies (SFE) of 0.8-0.9 at z>9, decreasing to 0.2-0.3 at lower redshifts. The analysis reveals that dust attenuation increases predicted star formation rates at z<8 and can push SFEs above unity at z>8, while adopting top-heavy initial mass functions reduces SFEs by factors of 2-3, suggesting variable IMFs may be necessary to explain high-redshift galaxy evolution.
Why it matters
This work addresses a fundamental challenge in cosmology regarding the unexpectedly high abundance of early galaxies observed by JWST, which traditional models struggle to explain. The findings suggest that our understanding of star formation processes, dust physics, and stellar initial mass functions may need revision for the early universe, with implications for interpreting observations of the first galaxies.
arXiv:2605.26209v1 Announce Type: new
Abstract: JWST has measured an unprecedented abundance of galaxies above $zgtrsim 4-5$, whose formation and evolution are still difficult to reconcile within traditional galaxy evolution models in a $Lambda$CDM framework. Here, we present a study on the star formation histories of these high-redshift galaxies between $zsimeq5-12$ via a data-driven semi-empirical model that uses the observed UV LFs as input to retrieve SFRs, naturally bypassing any uncertain modelling of cooling, feedback and/or stochastic processes. Galaxy stellar masses are progressively built in time by integrating their SFRs assigned along their progenitor haloes via the SFR-halo accretion rate relation, derived from abundance matching between the input observed UV LFs with the dark matter halo accretion rate distributions at each redshift. This makes the SFEs a full prediction of the model rather than a tuned input, serving as a natural baseline to test burstiness, dust attenuation, or IMF variations. Our approach naturally reproduces the total stellar mass function, the large-scale clustering, and the star-forming main sequence. We find that massive galaxies grew their stellar mass with a bursty star formation at $zsim9-10$, broadly in agreement with the star formation histories inferred from spectral energy distribution fitting, with the SFE reaching high peaks of $0.8-0.9$ at $z>9$ and lowering to standard values of $0.2-0.3$ below $zlesssim9$. We find that the presence of dust could enhance the predicted SFRs at $zlesssim8$, better reproducing the observed SFRs of massive dusty galaxies, and increase the SFEs to values close to or even above unity at $z gtrsim 8$. Finally, switching to top-heavy IMFs reduces the SFEs by a factor of $2-3$, highlighting the need for a variable IMF as an inevitable ingredient in the evolution of galaxies at high redshifts to avoid unphysical SFEs, especially in the presence of dust.