Discovery of HI gas in a young radio galaxy at $z = 0.44$ using the Australian Square Kilometre Array Pathfinder
Creators: name: Allison, J. R.
name: Sadler, E. M.
name: Moss, V. A.
name: Whiting, M. T.
name: Hunstead, R. W.
name: Pracy, M. B.
name: Curran, S. J.
name: Croom, S. M.
name: Glowacki, M.
name: Morganti, R.
name: Shabala, S. S.
name: Zwaan, M. A.
name: Allen, G.
name: Amy, S. W.
name: Axtens, P.
name: Ball, L.
name: Bannister, K. W.
name: Barker, S.
name: Bell, M. E.
name: Bock, D. C. -J.
name: Bolton, R.
name: Bowen, M.
name: Boyle, B.
name: Braun, R.
name: Broadhurst, S.
name: Brodrick, D.
name: Brothers, M.
name: Brown, A.
name: Bunton, J. D.
name: Cantrall, C.
name: Chapman, J.
name: Cheng, W.
name: Chippendale, A. P.
name: Chung, Y.
name: Cooray, F.
name: Cornwell, T.
name: DeBoer, D.
name: Diamond, P.
name: Edwards, P. G.
name: Ekers, R.
name: Feain, I.
name: Ferris, R. H.
name: Forsyth, R.
name: Gough, R.
name: Grancea, A.
name: Gupta, N.
name: Guzman, J. C.
name: Hampson, G.
name: Harvey-Smith, L.
name: Haskins, C.
name: Hay, S.
name: Hayman, D. B.
name: Heywood, I.
name: Hotan, A. W.
name: Hoyle, S.
name: Humphreys, B.
name: Indermuehle, B. T.
name: Jacka, C.
name: Jackson, C.
name: Jackson, S.
name: Jeganathan, K.
name: Johnston, S.
name: Joseph, J.
name: Kendall, R.
name: Kesteven, M.
name: Kiraly, D.
name: Koribalski, B. S.
name: Leach, M.
name: Lenc, E.
name: Lensson, E.
name: Mackay, S.
name: Macleod, A.
name: Marquarding, M.
name: Marvil, J.
name: McClure-Griffiths, N.
name: McConnell, D.
name: Mirtschin, P.
name: Norris, R. P.
name: Neuhold, S.
name: Ng, A.
name: O'Sullivan, J.
name: Pathikulangara, J.
name: Pearce, S.
name: Phillips, C.
name: Popping, A.
name: Qiao, R. Y.
name: Reynolds, J. E.
name: Roberts, P.
name: Sault, R. J.
name: Schinckel, A.
name: Serra, P.
name: Shaw, R.
name: Shields, M.
name: Shimwell, T.
name: Storey, M.
name: Sweetnam, T.
name: Troup, E.
name: Turner, B.
name: Tuthill, J.
name: Tzioumis, A.
name: Voronkov, M. A.
name: Westmeier, T.
name: Wilson, C. D.
Publisher: name: arXiv
Year: 2015
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We 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$-$517 and demonstrates ASKAP's excellent capability for performing a future wide-field survey for HI absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the HI gas is intrinsic to the host galaxy of the radio source. The narrow OIII emission lines show clear double-peaked structure, indicating either large-scale outflow or rotation of the ionized gas. Archival data from the \emph{XMM-Newton} satellite exhibit an absorbed X-ray spectrum that is consistent with a high column density obscuring medium around the active galactic nucleus. The HI absorption profile is complex, with four distinct components ranging in width from 5 to 300 km s$^{-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 $v \sim 300$ km s$^{-1}$. We infer that the expanding young radio source ($t_{\rm age} \approx 2500$ yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of $\sim$ 1 $\mathrm{M}_{\odot}$ yr$^{-1}$.
description: 18 pages, 11 figures, accepted for publication in MNRAS