Allison, J.R.Sadler, Elaine MMoss, V.A.Whiting, M.T.Hunstead, RichardCurran, S.J.Croom, Scott MGlowacki, M.Morganti, RaffaellaTzioumis, A KStorey, M.Sweetnam, T.Troup, E.Turner, B.Tuthill, J.Voronkov, M.A.Westmeier, T.Wilson, C.D.Zwaan, M APracy, MichaelShabala, Stanislav SZwaan, M.A.Allen, GAmy, S.W.Axtens, P.Ball, LewisBannister, KeithBarker, S.Bell, M.Bock, D. C.-J.Bolton, R.Bowen, M.Boyle, B.Braun, R.Broadhurst, S.Brodrick, D.Brothers, M.Brown, A.Bunton, John D.Cantrall, C.Chapman, J.Cheng, W.Chippendale, A.P.Chung, Y.Cooray, F.Cornwell, T.DeBoer, D.Diamond, P.Edwards, P GEkers, Ronald DFeain, IFerris, Richard HForsyth, R.Gough, RGrancea, A.Gupta, N.Guzman, J.C.Hampson, G.Harvey-Smith, L.Haskins, C.Hay, S.Hayman, D.B.Heywood, I.Hotan, A.W.Hoyle, S.Humphreys, B.Indermuehle, B.T.Jacka, C.Jackson, Carole AJackson, S.Jeganathan, K.Johnston, SJoseph, J.Kendall, R.Kesteven, M JKiraly, D.Koribalski, Baerbel SLeach, M.Lenc, EmilLensson, E.Mackay, S.Macleod, A.Marquarding, MMarvil, J.McClure-Griffiths, NaomiMcConnell, DMirtschin, P.Norris, R PNeuhold, S.Ng, A.O’Sullivan, J.Pathikulangara, JosephPearce, S.Phillips, CPopping, A.Qiao, R.Y.Reynolds, J ERoberts, P.Sault, Robert JSchinckel, A.Serra, P.Shaw, R.Shields, M.Shimwell, Timothy W2016-06-130035-8711http://hdl.handle.net/1885/102535We report the discovery of a new 21-cm HI absorption system using commissioning data from the Boolardy Engineering Test Array of the Australian Square Kilometre Array Pathfinder (ASKAP). Using the 711.5-1015.5 MHz band of ASKAP we were able to conduct a blind search for the 21-cm line in a continuous redshift range between z = 0.4 and 1.0, which has, until now, remained largely unexplored. The absorption line is detected at z = 0.44 towards the GHz-peaked spectrum radio source PKS B1740-517 and demonstrates ASKAP's excellent capability for performing a future wide-field survey for HI absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the HI gas is intrinsic to the host galaxy of the radio source. The narrow [OIII] emission lines show clear double-peaked structure, indicating either large-scale outflow or rotation of the ionized gas. Archival data from the XMM-Newton satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the active galactic nucleus. The HI absorption profile is complex, with four distinct components ranging in width from 5 to 300 km s-1 and fractional depths from 0.2 to 20 per cent. In addition to systemic HI gas, in a circumnuclear disc or ring structure aligned with the radio jet, we find evidence for a possible broad outflow of neutral gas moving at a radial velocity of v ~ 300 km s-1. We infer that the expanding young radio source (t<inf>age</inf> ≈ 2500 yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of ~1 M o˙ yr-1.Author/s retain copyright201510.1093/mnras/stv15322016-06-10