The 154 MHz radio sky observed by the Murchison Widefield Array: noise, confusion, and first source count analyses

Franzen, T. M. O.T. M. O.FranzenJackson, C. A.C. A.JacksonOffringa, A. R.A. R.OffringaEkers, R. D.R. D.EkersWayth, R. B.R. B.WaythBERNARDI, GIANNIGIANNIBERNARDI0000-0002-0916-7443Bowman, J. D.J. D.BowmanBriggs, F.F.BriggsCappallo, R. J.R. J.CappalloDeshpande, A. A.A. A.DeshpandeGaensler, B. M.B. M.GaenslerGreenhill, L. J.L. J.GreenhillHazelton, B. J.B. J.HazeltonJohnston-Hollitt, M.M.Johnston-HollittKaplan, D. L.D. L.KaplanLonsdale, C. J.C. J.LonsdaleMcWhirter, S. R.S. R.McWhirterMitchell, D. A.D. A.MitchellMorales, M. F.M. F.MoralesMorgan, E.E.MorganMorgan, J.J.MorganOberoi, D.D.OberoiOrd, S. M.S. M.OrdPrabu, T.T.PrabuSeymour, N.N.SeymourShankar, N. UdayaN. UdayaShankarSrivani, K. S.K. S.SrivaniSubrahmanyan, R.R.SubrahmanyanTingay, S. J.S. J.TingayTrott, C. M.C. M.TrottWebster, R. L.R. L.WebsterWilliams, A.A.WilliamsWilliams, C. L.C. L.Williams2020-07-032020-07-0320160035-8711http://hdl.handle.net/20.500.12386/26320We analyse a 154 MHz image made from a 12 h observation with the Murchison Widefield Array (MWA) to determine the noise contribution and behaviour of the source counts down to 30 mJy. The MWA image has a bandwidth of 30.72 MHz, a field-of-view within the half-power contour of the primary beam of 570 deg2, a resolution of 2.3 arcmin and contains 13 458 sources above 5σ. The rms noise in the centre of the image is 4-5 mJy beam-1. The MWA counts are in excellent agreement with counts from other instruments and are the most precise ever derived in the flux density range 30-200 mJy due to the sky area covered. Using the deepest available source count data, we find that the MWA image is affected by sidelobe confusion noise at the ≈3.5 mJy beam-1 level, due to incompletely peeled and out-of-image sources, and classical confusion becomes apparent at ≈1.7 mJy beam-1. This work highlights that (I) further improvements in ionospheric calibration and deconvolution imaging techniques would be required to probe to the classical confusion limit and (II) the shape of low-frequency source counts, including any flattening towards lower flux densities, must be determined from deeper ≈150 MHz surveys as it cannot be directly inferred from higher frequency data.STAMPAenThe 154 MHz radio sky observed by the Murchison Widefield Array: noise, confusion, and first source count analysesArticle10.1093/mnras/stw8232-s2.0-84975060929000379840900078https://academic.oup.com/mnras/article/459/3/3314/25952182016MNRAS.459.3314FFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering