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Source counts and confusion at 72–231 MHz in the MWA GLEAM survey

Published online by Cambridge University Press:  11 February 2019

T. M. O. Franzen
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands
T. Vernstrom
Affiliation:
Dunlap Institute for Astronomy and Astrophysics, University of Toronto, ON, M5S 3H4, Canada
C. A. Jackson
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), 44 Rosehill Street Redfern, NSW 2016, Australia
N. Hurley-Walker
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
R. D. Ekers
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
G. Heald
Affiliation:
CSIRO Astronomy and Space Science, PO Box 1130, Bentley, WA 6102, Australia
N. Seymour
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
S. V. White
Affiliation:
International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
Corresponding
E-mail address:

Abstract

The GaLactic and Extragalactic All-sky Murchison Widefield Array survey is a radio continuum survey at 72–231 MHz of the whole sky south of declination +30º, carried out with the Murchison Widefield Array. In this paper, we derive source counts from the GaLactic and Extragalactic All-sky Murchison data at 200, 154, 118, and 88 MHz, to a flux density limit of 50, 80, 120, and 290 mJy respectively, correcting for ionospheric smearing, incompleteness and source blending. These counts are more accurate than other counts in the literature at similar frequencies as a result of the large area of sky covered and this survey’s sensitivity to extended emission missed by other surveys. At S154 MHz > 0.5 Jy, there is no evidence of flattening in the average spectral index (α ≈ −0.8 where Svα) towards the lower frequencies. We demonstrate that the Square Kilometre Array Design Study model by Wilman et al. significantly underpredicts the observed 154-MHz GaLactic and Extragalactic All-sky Murchison counts, particularly at the bright end. Using deeper Low-Frequency Array counts and the Square Kilometre Array Design Study model, we find that sidelobe confusion dominates the thermal noise and classical confusion at v ≳ 100 MHz due to both the limited CLEANing depth and the undeconvolved sources outside the field-of-view. We show that we can approach the theoretical noise limit using a more efficient and automated CLEAN algorithm.

Type
Research Article
Copyright
© Astronomical Society of Australia 2019 

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Source counts and confusion at 72–231 MHz in the MWA GLEAM survey
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