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COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission

Algera, Hiddo S.B.; Hodge, Jacqueline A.; Riechers, Dominik A.; Leslie, Sarah K.; Smail, Ian; Aravena, Manuel; Cunha, Elisabete da; Daddi, Emanuele; Decarli, Roberto; Dickinson, Mark; Gim, Hansung B.; Guaita, Lucia; Magnelli, Benjamin; Murphy, Eric J.; Pavesi, Riccardo; Sargent, Mark T.; Sharon, Chelsea E.; Wagg, Jeff; Walter, Fabian; Yun, Min

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Authors

Hiddo S.B. Algera

Jacqueline A. Hodge

Dominik A. Riechers

Sarah K. Leslie

Manuel Aravena

Elisabete da Cunha

Emanuele Daddi

Roberto Decarli

Mark Dickinson

Hansung B. Gim

Lucia Guaita

Benjamin Magnelli

Eric J. Murphy

Riccardo Pavesi

Mark T. Sargent

Chelsea E. Sharon

Jeff Wagg

Fabian Walter

Min Yun



Abstract

Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5  z  3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation.

Citation

Algera, H. S., Hodge, J. A., Riechers, D. A., Leslie, S. K., Smail, I., Aravena, M., …Yun, M. (2022). COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission. Astrophysical Journal, 924(2), https://doi.org/10.3847/1538-4357/ac34f5

Journal Article Type Article
Acceptance Date Oct 28, 2021
Online Publication Date Jan 13, 2022
Publication Date 2022
Deposit Date Mar 15, 2022
Publicly Available Date Mar 29, 2024
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 924
Issue 2
DOI https://doi.org/10.3847/1538-4357/ac34f5

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