# Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS): II. Cold Molecular Gas Evolution out to Redshift 6

**Authors:** Daizhong Liu, E. Schinnerer, B. Groves, B. Magnelli, P. Lang, S. Leslie, E. Jimenez-Andrade, D. A. Riechers, G. Popping, Georgios E. Magdis, E. Daddi, M. Sargent, Yu Gao, Y. Fudamoto, P. A. Oesch, F. Bertoldi  
**arXiv:** [1910.12883](https://arxiv.org/abs/1910.12883)  
**Date:** 2019-10-28  
**Summary page:** https://www.summarizepaper.com/en/paper/1910.12883v1/

## Key points

- Researchers present new measurements of the cosmic cold molecular gas evolution out to redshift 6
- The study is based on systematic mining of the ALMA public archive in the COSMOS deep field (A3COSMOS)
- The team compared multiple gas mass calibration methods and tested biases in band conversions from observed ALMA wavelength to rest-frame Rayleigh-Jeans(RJ)-tail continuum
- Combining their A3COSMOS sample with approximately 1,000 CO-observed galaxies at 0 < z < 4 (75% at z < 0.1), they parameterized galaxies' molecular gas depletion time and molecular gas to stellar mass ratio (gas fraction) each as a function of stellar mass, offset from the star-forming main sequence (Delta MS), and cosmic age or redshift
- Their proposed functional form provides a statistically better fit to current data than existing functional forms in literature, implying a "downsizing" effect where more massive galaxies evolve earlier than less massive ones, and "mass-quenching," where gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones
- The team adopted galaxy stellar mass functions and applied their function for gas mass calculation to infer the cosmic cold molecular gas density evolution out to redshift 6 for the first time
- They found agreement with CO blind surveys as well as semi-analytic modeling, providing a coherent picture of cold molecular gas, star formation rate (SFR), and stellar mass evolution in galaxies across cosmic time

## Summary

In a recent study, researchers present new measurements of the cosmic cold molecular gas evolution out to redshift 6. The study is based on systematic mining of the ALMA public archive in the COSMOS deep field (A3COSMOS), which contains approximately 700 galaxies with high-confidence ALMA detections in both the (sub-)millimeter continuum and multi-wavelength spectral energy distributions (SEDs). The team compared multiple gas mass calibration methods and tested biases in band conversions from observed ALMA wavelength to rest-frame Rayleigh-Jeans(RJ)-tail continuum. Combining their A3COSMOS sample with approximately 1,000 CO-observed galaxies at 0 < z < 4 (75% at z < 0.1), they parameterized galaxies' molecular gas depletion time and molecular gas to stellar mass ratio (gas fraction) each as a function of stellar mass, offset from the star-forming main sequence (Delta MS), and cosmic age or redshift. Their proposed functional form provides a statistically better fit to current data than existing functional forms in literature, implying a "downsizing" effect where more massive galaxies evolve earlier than less massive ones, and "mass-quenching," where gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones. The team adopted galaxy stellar mass functions and applied their function for gas mass calculation to infer the cosmic cold molecular gas density evolution out to redshift 6 for the first time. They found agreement with CO blind surveys as well as semi-analytic modeling, providing a coherent picture of cold molecular gas, star formation rate (SFR), and stellar mass evolution in galaxies across cosmic time. Overall, this study presents important new insights into our understanding of how cold molecular gas evolves over time within galaxies. These findings have significant implications for our understanding of galaxy formation and evolution throughout cosmic history.