COSMOS-Web: Star formation along the early Hubble sequence and the evolution of dust over the redshift range 0<z<12
Pith reviewed 2026-05-20 03:52 UTC · model grok-4.3
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The pith
Mean star-formation rate of massive galaxies at 2<z<4.5 falls from 280 to 80 solar masses per year along the Hubble sequence from irregulars to spheroids.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the redshift range 2 < z < 4.5 the mean star-formation rate for the most massive galaxies falls along the Hubble sequence from ~280 solar masses per year for irregular galaxies to ~80 for spheroids, showing that quenching was already occurring shortly after the emergence of the Hubble sequence. A chemical evolution model with outflow rate equal to the star-formation rate reproduces the monotonic rise in dust-to-stellar mass ratio out to z~8 and the relationship between mean dust density and redshift.
What carries the argument
Stacking analysis of 850-micron flux densities from the COSMOS-Web catalogue, split by stellar mass and morphological class and converted to star-formation rates and dust masses.
If this is right
- The transformation of submillimetre galaxies can reproduce the observed growth in number density of massive bulge-dominated and spheroidal galaxies over 1.5 < z < 4.
- A starvation quenching model with a depletion time of ~10^{8.2} years accounts for the lower star-formation rates measured in spheroids.
- The dust-to-stellar mass ratio increases monotonically with redshift out to z~8.
- The mean cosmic dust density follows a specific relation with redshift over 0 < z < 12 that the same chemical model reproduces.
Where Pith is reading between the lines
- If the morphological trend holds, current galaxy-formation simulations may need to introduce quenching physics at earlier epochs than most implementations assume.
- The same outflow-equals-star-formation chemical model could be tested against dust measurements in the local universe to check consistency across cosmic time.
- Deeper submillimeter surveys that reach lower stellar masses at z>4.5 could reveal whether the Hubble-sequence dependence of star formation persists or changes.
Load-bearing premise
Morphological classifications remain reliable and unbiased out to redshift 12 and the 850-micron flux provides an unbiased tracer of star-formation rate with negligible contamination from AGN or other sources.
What would settle it
High-resolution imaging that reclassifies a substantial fraction of the high-redshift sample into different morphological types with correspondingly different stacked fluxes would falsify the claimed decline along the Hubble sequence.
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