COSMOS-Web: Star formation along the early Hubble sequence and the evolution of dust over the redshift range 0<z<12
Pith reviewed 2026-05-21 07:43 UTC · model grok-4.3
The pith
Mean star-formation rates in the most massive galaxies fall along the Hubble sequence from irregular to spheroid types between redshifts 2 and 4.5, showing quenching began shortly after the sequence emerged.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Stacking analysis of 850-micron emission reveals that, for the most massive galaxies, mean star-formation rate declines along the Hubble sequence from irregular galaxies at one end to spheroids at the other in the redshift window 2<z<4.5. This trend indicates that quenching was already operating soon after the Hubble sequence appeared. The decline can be matched by a starvation model with a depletion time of 10^8.2 years, while the observed growth in number density of massive bulge-dominated and spheroidal galaxies between 1.5<z<4 is reproduced by the transformation of submillimetre galaxies. A chemical-evolution model built on the cosmic star-formation history and equal gas outflow rate is,
What carries the argument
Stacking of SCUBA-2 850-micron images for galaxies classified by morphology along the Hubble sequence and stellar mass
Load-bearing premise
The 850-micron stacked emission is produced almost entirely by dust heated by star formation with negligible AGN or other contamination, and that morphological types remain reliably assigned at redshifts above 2.
What would settle it
A measurement showing that AGN contribute more than a few tens of percent of the stacked 850-micron flux for the high-redshift samples, or a reclassification of the same galaxies with higher-resolution imaging that removes the systematic drop in star-formation rate from irregulars to spheroids.
Figures
read the original abstract
We have carried out a stacking analysis with the COSMOS-Web catalogue on one of the deepest ever SCUBA-2 images at 850 microns, allowing us to estimate the mean submillimetre flux density for samples of galaxies split by stellar mass and morphological class over the redshift range 0<z<12. For all morphological classes, the mean star-formation rate estimated from the dust emission increases with redshift, reaching a value for the most massive galaxies (~10^11 soar masses) of >~80 solar masses per year at 2 < z < 4.5. In this redshift range, the mean star-formation rate for these galaxies falls along the Hubble sequence from ~280 solar masses per year for irregular galaxies at one end to ~80 solar masses per year for spheroids at the other end, which shows that quenching was already happening shortly after the emergence of the Hubble sequence. The decrease in the star-formation rate for the spheroidal galaxies can be reproduced with a `starvation' quenching model with a depletion time of ~10^{8.2} years. We also show that the transformation of `submillimetre galaxies' can reproduce the growth in number-density of massive bulge-dominated and spheroidal galaxies over the redshift range 1.5 <z < 4. As a side-project, we have used our stacking results to show that the ratio of dust mass to stellar mass in galaxies increases with redshift out to z~8 and to determine the relationship between the mean density of dust and redshift in the range 0 < z <12. We show that a chemical evolution model based on the `star-formation history' of the universe, with a gas outflow rate equal to the star-formation rate, can explain the monotonic rise in the dust-to-stellar mass ratio and reproduce the relationship between mean dust density and redshift remarkably accurately.
Editorial analysis