COLDz: Shape of the CO Luminosity Function at High Redshift and the Cold Gas History of the Universe

Riechers, Dominik A.; Pavesi, Riccardo; Sharon, Chelsea E.; Hodge, Jacqueline A.; Decarli, Roberto; Walter, Fabian; Carilli, Christopher L.; Aravena, Manuel; da Cunha, Elisabete; Daddi, Emanuele; Dickinson, Mark; Smail, Ian; Capak, Peter L.; Ivison, Rob J.; Sargent, Mark; Scoville, Nicholas Z.; Wagg, Jeff

doi:10.3847/1538-4357/aafc27

COLDz: Shape of the CO Luminosity Function at High Redshift and the Cold Gas History of the Universe

Riechers, Dominik A.; Pavesi, Riccardo; Sharon, Chelsea E.; Hodge, Jacqueline A.; Decarli, Roberto; Walter, Fabian; Carilli, Christopher L.; Aravena, Manuel; da Cunha, Elisabete; Daddi, Emanuele; Dickinson, Mark; Smail, Ian; Capak, Peter L.; Ivison, Rob J.; Sargent, Mark; Scoville, Nicholas Z.; Wagg, Jeff

Authors

Dominik A. Riechers

Riccardo Pavesi

Chelsea E. Sharon

Jacqueline A. Hodge

Roberto Decarli

Fabian Walter

Christopher L. Carilli

Manuel Aravena

Elisabete da Cunha

Emanuele Daddi

Mark Dickinson

Professor Ian Smail ian.smail@durham.ac.uk
Emeritus Professor

Peter L. Capak

Rob J. Ivison

Mark Sargent

Nicholas Z. Scoville

Jeff Wagg

Abstract

We report the first detailed measurement of the shape of the CO luminosity function at high redshift, based on >320 hr of the NSF's Karl G. Jansky Very Large Array (VLA) observations over an area of ~60 arcmin2 taken as part of the CO Luminosity Density at High Redshift (COLDz) survey. COLDz "blindly" selects galaxies based on their cold gas content through CO(J = 1 → 0) emission at z ~ 2–3 and CO(J = 2 → 1) at z ~ 5–7 down to a CO luminosity limit of log(${L}_{\mathrm{CO}}^{{\prime} }$/K km s−1 pc2) sime 9.5. We find that the characteristic luminosity and bright end of the CO luminosity function are substantially higher than predicted by semi-analytical models, but consistent with empirical estimates based on the infrared luminosity function at z ~ 2. We also present the currently most reliable measurement of the cosmic density of cold gas in galaxies at early epochs, i.e., the cold gas history of the universe, as determined over a large cosmic volume of ~375,000 Mpc3. Our measurements are in agreement with an increase of the cold gas density from z ~ 0 to z ~ 2–3, followed by a possible decline toward z ~ 5–7. These findings are consistent with recent surveys based on higher-J CO line measurements, upon which COLDz improves in terms of statistical uncertainties by probing ~50–100 times larger areas and in the reliability of total gas mass estimates by probing the low-J CO lines accessible to the VLA. Our results thus appear to suggest that the cosmic star formation rate density follows an increased cold molecular gas content in galaxies toward its peak about 10 billion years ago, and that its decline toward the earliest epochs is likely related to a lower overall amount of cold molecular gas (as traced by CO) bound in galaxies toward the first billion years after the Big Bang.

Citation

Riechers, D. A., Pavesi, R., Sharon, C. E., Hodge, J. A., Decarli, R., Walter, F., …Wagg, J. (2019). COLDz: Shape of the CO Luminosity Function at High Redshift and the Cold Gas History of the Universe. Astrophysical Journal, 872(1), Article 7. https://doi.org/10.3847/1538-4357/aafc27

Journal Article Type	Article
Acceptance Date	Jan 4, 2019
Online Publication Date	Feb 6, 2019
Publication Date	Feb 10, 2019
Deposit Date	Feb 20, 2019
Publicly Available Date	Feb 20, 2019
Journal	Astrophysical Journal
Print ISSN	0004-637X
Publisher	American Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	872
Issue	1
Article Number	7
DOI	https://doi.org/10.3847/1538-4357/aafc27