The LOFAR window on star-forming galaxies and AGNs – curved radio SEDs and IR–radio correlation at 0<z<2.5

Calistro Rivera, G. and Williams, W.L. and Hardcastle, M.J. and Duncan, K. and Rottgering, H.J.A. and Best, P.N. and Brüggen, M. and Chyży, K.T. and Conselice, C.J. and de Gasperin, F. and Engels, D. and Gürkan, G. and Intema, H.T. and Jarvis, M.J. and Mahony, E.K. and Miley, G.K. and Morabito, L.K. and Prandoni, I. and Sabater, J. and Smith, D.J.B. and Tasse, C. and van der Werf, P.P. and White, G.J. (2017) The LOFAR window on star-forming galaxies and AGNs – curved radio SEDs and IR–radio correlation at 0<z<2.5. Monthly Notices of the Royal Astronomical Society, 469 (3). pp. 3468-3488. ISSN 1365-2966

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We present a study of the low-frequency radio properties of star-forming (SF) galaxies and active galactic nuclei (AGNs) up to redshift z = 2.5. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of 1542 galaxies in ∼ 7 deg2 of the LOFAR Boötes field. Using the extensive multiwavelength data set available in Boötes and detailed modelling of the far-infrared to ultraviolet spectral energy distribution (SED), we are able to separate the star formation (N = 758) and the AGN (N = 784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGNs. We investigate the redshift evolution of the infrared–radio correlation for SF galaxies and find that the ratio of total infrared to 1.4-GHz radio luminosities decreases with increasing redshift: q1.4 GHz = (2.45 ± 0.04) (1 + z)−0.15 ± 0.03. Similarly, q150 MHz shows a redshift evolution following q150 GHz = (1.72 ± 0.04) (1 + z)−0.22 ± 0.05. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from q1.4 GHz is not an accurate approximation at all redshifts.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Keywords: galaxies: evolution, galaxies: nuclei, galaxies: photometry, galaxies: starburst, infrared: galaxies, radio continuum: galaxies
Schools/Departments: University of Nottingham, UK > Faculty of Science > School of Physics and Astronomy
Identification Number: 10.1093/mnras/stx1040
Depositing User: Eprints, Support
Date Deposited: 15 Jun 2017 12:01
Last Modified: 13 Oct 2017 00:03

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