Nowhere to Hide: Radio-faint AGN in GOODS-N field

I. Initial catalogue and radio properties^⋆

¹ Kapteyn Astronomical Institute, University of Groningen, 9747 AD Groningen, The Netherlands
² Jodrell Bank Centre for Astrophysics/e-MERLIN, The University of Manchester, M13 9PL Manchester, UK
e-mail: jack.radcliffe@manchester.ac.uk
³ ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia
⁶ Joint Institute for VLBI ERIC, Postbus 2, 7990 AA Dwingeloo, The Netherlands

Received: 9 May 2018
Accepted: 31 July 2018

Abstract

Context. The occurrence of active galactic nuclei (AGN) is critical to our understanding of galaxy evolution and formation. Radio observations provide a crucial, dust-independent tool to study the role of AGN. However, conventional radio surveys of deep fields ordinarily have arc-second scale resolutions often insufficient to reliably separate radio emission in distant galaxies originating from star-formation and AGN-related activity. Very long baseline interferometry (VLBI) can offer a solution by identifying only the most compact radio emitting regions in galaxies at cosmological distances where the high brightness temperatures (in excess of 10⁵ K) can only be reliably attributed to AGN activity.

Aims. We present the first in a series of papers exploring the faint compact radio population using a new wide-field VLBI survey of the GOODS-N field. This will expand upon previous surveys, permitting the characterisation of the faint, compact radio source population in the GOODS-N field. The unparalleled sensitivity of the European VLBI Network (EVN) will probe a luminosity range rarely seen in deep wide-field VLBI observations, thus providing insights into the role of AGN to radio luminosities of the order 10²² WHz⁻¹ across cosmic time.

Methods. The newest VLBI techniques are used to completely cover an entire 7′̣5 radius area to milliarcsecond resolutions, while bright radio sources (S > 0.1 mJy) are targeted up to 25′ from the pointing centre. Multi-source self-calibration, and a primary beam model for the EVN array are used to correct for residual phase errors and primary beam attenuation respectively.

Results. This paper presents the largest catalogue of VLBI detected sources in GOODS-N comprising of 31 compact radio sources across a redshift range of 0.11–3.44, almost three times more than previous VLBI surveys in this field. We provide a machine-readable catalogue and introduce the radio properties of the detected sources using complementary data from the e-MERLIN Galaxy Evolution survey (eMERGE).