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COLDz: probing cosmic star formation with radio free-free emission

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Version 2 2023-06-12, 07:39
Version 1 2023-06-10, 02:06
journal contribution
posted on 2023-06-12, 07:39 authored by Hiddo S B Algera, Jacqueline A Hodge, Dominik A Riechers, Sarah K Leslie, Ian Smail, Manuel Aravena, Elisabete da Cunha, Emanuele Daddi, Roberto Decarli, Mark Dickinson, Hansung B Gim, Lucia Guaita, Benjamin Magnelli, Eric J Murphy, Mark Sargent, others
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 multi-frequency 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× 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 multi-frequency 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.

Funding

University of Sussex Astronomy Consolidated Grant 2020-2023; G2954; STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCIL; ST/T000473/1

History

Publication status

  • Published

File Version

  • Published version

Journal

Astrophysical Journal

ISSN

0004-637X

Publisher

IOP Publishing

Issue

2

Volume

924

Page range

1-20

Department affiliated with

  • Physics and Astronomy Publications

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date

2022-01-04

First Open Access (FOA) Date

2022-03-07

First Compliant Deposit (FCD) Date

2022-01-03

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