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The VLA-COSMOS 3 GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to z ≲ 6

Delhaize, J. and Capak, P. (2017) The VLA-COSMOS 3 GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to z ≲ 6. Astronomy and Astrophysics, 602 . Art. No. A4. ISSN 0004-6361.

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We examine the behaviour of the infrared-radio correlation (IRRC) over the range 0 <z ≲ 6 using new, highly sensitive 3 GHz observations with the Karl G. Jansky Very Large Array (VLA) and infrared data from the Herschel Space Observatory in the 2 deg^2 COSMOS field. We distinguish between objects where emission is believed to arise solely from star-formation, and those where an active galactic nucleus (AGN) is thought to be present. We account for non-detections in the radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio (q_(TIR)), decreases with increasing redshift: q_(TIR)(z) = (2.88 ± 0.03)(1 + z)^(−0.19 ± 0.01). This is consistent with several previous results from the literature. Moderate-to-high radiative luminosity AGN do not follow the same q_(TIR)(z) trend as star-forming galaxies, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed q_(TIR)(z) trend of the star-forming galaxy population. We demonstrate that the choice of the average radio spectral index directly affects the normalisation, as well as the derived trend with redshift of the IRRC. An increasing fractional contribution to the observed 3 GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect K corrections in the radio may govern the derived trend of decreasing q_(TIR) with increasing redshift. A more detailed understanding of the radio spectrum is therefore required for robust K corrections in the radio and to fully understand the cosmic evolution of the IRRC. Lastly, we present a redshift-dependent relation between rest-frame 1.4 GHz radio luminosity and star formation rate taking the derived redshift trend into account.

Item Type:Article
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URLURL TypeDescription Paper
Delhaize, J.0000-0002-6149-0846
Additional Information:© 2017 ESO. Article published by EDP Sciences. Received 29 July 2016; Accepted 17 February 2017; Published online 13 June 2017. We thank the anonymous referee for useful comments which have helped to improve this paper. We also thank Tijana Prodanović for valuable discussions. This research was funded by the European Unions Seventh Frame-work programme under grant agreement 337595 (ERC Starting Grant, “CoSMass”). This research was supported by the Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence “Origin and Structure of the Universe”. N.B. acknowledges the European Unions Seventh Framework programme under grant agreement 333654 (CIG, AGN feedback). M.B. and P. Ciliegi acknowledge support from the PRIN-INAF 2014. A.K. acknowledges support by the Collaborative Research Council 956, sub-project A1, funded by the Deutsche Forschungsgemeinschaft (DFG). M.T.S. acknowledges support from a Royal Society Leverhulme Trust Senior Research Fellowship. Support for B.M. was provided by the DFG priority programme 1573 “The physics of the interstellar medium”. M.A. acknowledges partial support from FONDECYT through grant 1140099.
Funding AgencyGrant Number
European Research Council (ERC)337595
Munich Institute for Astro- and Particle Physics (MIAPP)UNSPECIFIED
European Research Council (ERC)333654
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)956
Leverhulme TrustUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)1573
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1140099
Subject Keywords:galaxies: evolution – galaxies: star formation – radio continuum: galaxies – infrared: galaxies
Record Number:CaltechAUTHORS:20170928-104505397
Persistent URL:
Official Citation:The VLA-COSMOS 3 GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to z ≲ 6 J. Delhaize, V. Smolčić, I. Delvecchio, M. Novak, M. Sargent, N. Baran, B. Magnelli, G. Zamorani, E. Schinnerer, E. J. Murphy, M. Aravena, S. Berta, M. Bondi, P. Capak, C. Carilli, P. Ciliegi, F. Civano, O. Ilbert, A. Karim, C. Laigle, O. Le Fèvre, S. Marchesi, H. J. McCracken, M. Salvato, N. Seymour and L. Tasca A&A, 602 (2017) A4 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81896
Deposited By: Tony Diaz
Deposited On:28 Sep 2017 18:22
Last Modified:28 Sep 2017 18:22

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