COSMOS-Web: The emergence of the Hubble Sequence

The first JWST deep surveys have opened a new window into understanding the morphological evolution of galaxies across cosmic time. The improved spatial resolution and near-infrared (NIR) coverage have revealed a population of morphologically evolved galaxies at very early epochs. However, all previous works are based on small-number statistics, preventing accurate probing of the morphological diversity at cosmic dawn. Aims. Leveraging the wide area coverage of the COSMOS-Web survey, we quantify the abundance of different morphological types from z ∼ 7 with unprecedented statistics and establish robust constraints on the epoch of emergence of the Hubble sequence. Methods. We measure the global (spheroids, disk-dominated, bulge-dominated, peculiar) and resolved (stellar bars) morphologies for about 400,000 galaxies down to F150W = 27 using deep learning, representing a two-orders-of-magnitude increase over previous studies. We then provide reference Stellar Mass Functions (SMFs) of different morphologies between z ∼ 0.2 and z ∼ 7 as well as best-fit parameters to inform models of galaxy formation. All catalogs and data are made publicly available. Results. (a) At redshift z > 4.5, the massive galaxy population (log M∗/M > 10) is dominated by disturbed morphologies (∼ 70%) - even in the optical rest frame - and very compact objects (∼ 30%) with effective radii smaller than ∼ 500 pc. This confirms that a significant fraction of the star formation at cosmic dawn occurs in very dense regions, although the stellar mass for these systems could be overestimated. (b) Galaxies with Hubble-type morphologies—including bulge- and disk-dominated galaxies—arose rapidly around z ∼ 4 and dominate the morphological diversity of massive galaxies as early as z ∼ 3. (c) Using stellar bars as a proxy, we speculate that stellar disks in massive galaxies might have been common (> 50%) among the star-forming population since cosmic noon (z ∼ 2–2.5) and formed as early as z ∼ 7. (d) Massive quenched galaxies are predominantly bulge-dominated from z ∼ 4 onward, suggesting that morphological transformations briefly precede or are simultaneous to quenching mechanisms at the high-mass end. (e) Low-mass (log M∗/M < 10) quenched galaxies are typically disk-dominated, pointing to different quenching routes in the two ends of the stellar mass spectrum from cosmic dawn