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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Sub-millimetre source identifications and the microjansky source population at 8.4ghz in thewilliam herschel deep field
Monthly Notices of the Royal Astronomical Society, Volume 428, No. 2, Year 2013
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Description
Sub-millimetre observations of the William Herschel Deep Field (WHDF) using the Large Apex Bolometer Camera (LABOCA) revealed possible sub-mm counterparts for two X-rayabsorbed quasars. The primary aim here is to exploit ExpandedVery LargeArray (EVLA) radio continuum imaging at 8.4GHz to establish the absorbed quasars as radio/sub-mm sources. The main challenge in reducing the WHDF EVLA data was the presence of a strong 4C source at the field edge. A new calibration algorithm was applied to the data to model and subtract this source. The resulting thermal noise limited radiomap covers a sky area which includes the 16× 16arcmin2 Extended WHDF. It contains 41 radio sources above the 4σ detection threshold, 17 of which have primary beam corrected flux densities. The radio observations show that the two absorbed active galactic nuclei (AGN) with LABOCA detections are also coincident with radio sources, confirming the tendency for X-ray-absorbed AGN to be sub-mm bright. These two sources also show strong ultraviolet excess (UVX) which suggest that the nuclear sightline is gas absorbed but not dust absorbed. Of the three remaining LABOCA sources within the ≈5arcmin half-power diameter of the EVLA primary beam, one is identified with a faint nuclear X-ray/radio source in a nearby galaxy, one with a faint radio source and the other is unidentified in any other band. More generally, differential radio source counts calculated from the beam-corrected data are in good agreement with previous observations, showing atS < 50μJy a significant excess over a pure AGN model. In the full area, of 10 sources fainter than this limit, six have optical counterparts of which three are UVX (i.e. likely quasars) including the two absorbed quasar LABOCA sources. The other faint radio counterparts are not UVX but are only slightly less blue and likely to be star-forming/merging galaxies, predominantly at lower luminosities and redshifts. The four faint, optically unidentified radio sources may be either dust-obscured quasars or galaxies. These high-redshift obscured AGN and lower redshift star-forming populations are thus the main candidates to explain the observed excess in the faint source counts and hence also the excess radio background found previously by the Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE2) experiment. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Authors & Co-Authors
Heywood, Ian
United Kingdom, Oxford
University of Oxford
South Africa, Grahamstown
Rhodes University
Bielby, Richard M.
United Kingdom, Durham
Durham University
Hill, Michael D.
United Kingdom, Durham
Durham University
Metcalfe, Nigel
United Kingdom, Durham
Durham University
Rawlings, Steve G.
United Kingdom, Oxford
University of Oxford
Shanks, Tom
United Kingdom, Durham
Durham University
Smirnov, Oleg M.
South Africa, Grahamstown
Rhodes University
South Africa, Pinelands
Square Kilometre Array, South Africa
Statistics
Citations: 8
Authors: 7
Affiliations: 4
Identifiers
Doi:
10.1093/mnras/sts046
ISSN:
00358711
e-ISSN:
13652966
Research Areas
Cancer
Environmental
Study Design
Cross Sectional Study
Study Approach
Quantitative