Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS). II. Cold Molecular Gas Evolution out to Redshift 6
Abstract
We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the Atacama Large Millimeter/submillimeter Array (ALMA) public archive in the COSMOS deep field (A3COSMOS). Our A3COSMOS data set contains ∼700 galaxies (0.3 ≲ z ≲ 6) with high-confidence ALMA detections in the (sub)millimeter continuum and multiwavelength spectral energy distributions. Multiple gas mass calibration methods are compared, and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans tail continuum) have been tested. Combining our A3COSMOS sample with ∼1000 CO-observed galaxies at 0 ≲ z ≲ 4 (75% at z < 0.1), we parameterize galaxies’ molecular gas depletion time ({τ }depl}) and molecular gas to stellar mass ratio ({μ }molgas}) each as a function of the stellar mass ({M}\star ), offset from the star-forming main sequence ({{Δ }}{MS}) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature) and implies a “downsizing” effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and “mass quenching” (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our {μ }molgas} function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semianalytic modeling. These together provide a coherent picture of cold molecular gas, star formation rate, and stellar mass evolution in galaxies across cosmic time.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2019
- DOI:
- 10.3847/1538-4357/ab578d
- arXiv:
- arXiv:1910.12883
- Bibcode:
- 2019ApJ...887..235L
- Keywords:
-
- Galaxy evolution;
- High-redshift galaxies;
- Interstellar medium;
- Submillimeter astronomy;
- 594;
- 734;
- 847;
- 1647;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 41 pages, 23 figures, 3 tables, resubmitted to ApJ after addressing referee's comments. Meanwhile we provide a Python package to calculate our gas evolution function ( https://ascl.net/code/v/2377 )