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The eMERGE Survey - I: very large array 5.5 GHz observations of the GOODS-North field.

Guidetti, D. and Bondi, M. and Prandoni, I. and Muxlow, T.W.B. and Beswick, R. and Wrigley, N. and Smail, I. and McHardy, I. and Thomson, A.P. and Radcliffe, J. and Argo, M.K. (2017) 'The eMERGE Survey - I: very large array 5.5 GHz observations of the GOODS-North field.', Monthly notices of the Royal Astronomical Society., 471 (1). pp. 210-226.


We present new observations of the GOODS-N field obtained at 5.5 GHz with the Karl G. Jansky Very Large Array. The central region of the field was imaged to a median rms of 3 μJy beam−1 with a resolution of 0.5 arcsec. From a 14-arcmin diameter region, we extracted a sample of 94 radio sources with signal-to-noise ratio greater than 5. Near-IR identifications are available for about ∼88 per cent of the radio sources. We used different multiband diagnostics to separate active galactic nuclei (AGNs), both radiatively efficient and inefficient, from star-forming galaxies. From our analysis, we find that about 80 per cent of our radio-selected sample is AGN dominated, with the fraction rising to 92 per cent when considering only the radio sources with redshift >1.5. This large fraction of AGN-dominated radio sources at very low flux densities (the median flux density at 5.5 GHz is 42 μJy), where star-forming galaxies are expected to dominate, is somewhat surprising and at odds with other results. Our interpretation is that both the frequency and angular resolution of our radio observations strongly select against radio sources whose brightness distribution is diffuse on a scale of several kpc. Indeed, we find that the median angular sizes of the AGN-dominated sources is around 0.2–0.3 arcsec against 0.8 arcsec for star-forming galaxies. This highlights the key role that high frequency radio observations can play in pinpointing AGN-driven radio emission at μJy levels. This work is part of the eMERGE legacy project.

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Publisher statement: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.
Date accepted:10 May 2017
Date deposited:22 August 2017
Date of first online publication:15 July 2017
Date first made open access:22 August 2017

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