paper

pop-cosmos: Star formation over 12 Gyr from generative modelling of a deep infrared-selected galaxy catalogue

arXiv:2509.20430 · doi:10.1093/mnras/stag764

Abstract

We study star formation over 12 Gyr using pop-cosmos, a generative model trained on 26-band photometry of 420,000 COSMOS2020 galaxies (IRAC Ch.1 ). The model learns distributions over 16 SPS parameters via score-based diffusion, matching observed colours and magnitudes. We compute the star formation rate density (SFRD) to by directly integrating individual galaxy SFRs. The SFRD peaks at , with peak value M yr Mpc. We classify star-forming (SF) and quiescent (Q) galaxies using specific SFR yr, comparing with colour selection. The sSFR criterion yields up to 20% smaller quiescent fractions across , with -selected samples contaminated by galaxies with sSFR up to yr. Our sSFR-selected stellar mass function shows a negligible number density of low-mass ( M) Q galaxies at , where colour-selection shows a prominent increase. Non-parametric star formation histories around the SFRD peak reveal distinct patterns: SF galaxies show gradually decreasing SFR correlations with lookback time ( to over 13 Gyr), implying increasingly stochastic star formation toward early epochs. Q galaxies exhibit full correlation () during the most recent 300 Myr, then sharp decorrelation with earlier star-forming epochs, marking clear quenching transitions. Massive (M) galaxies quench on a time-scale of Gyr, with mass assembly concentrated in their first 3.5 Gyr. Finally, AGN activity (infrared luminosity) peaks as massive ( M) galaxies approach the transition between star-forming and quiescent states, declining sharply once quiescence is established. This provides evidence that AGN feedback operates in a critical regime during the Gyr quenching transition.

arXiv comment26 pages, 17 figures, accepted for publication at MNRAS

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