Discovery of HI gas in a young radio galaxy at z = 0.44 using the Australian square kilometre array pathfinder

J. R. Allison*, E. M. Sadler, V. A. Moss, M. T. Whiting, R. W. Hunstead, M. B. Pracy, S. J. Curran, S. M. Croom, M. Glowacki, R. Morganti, S. S. Shabala, M. A. Zwaan, G. Allen, S. W. Amy, P. Axtens, L. Ball, K. W. Bannister, S. Barker, M. E. Bell, D. C.J. BockR. Bolton, M. Bowen, B. Boyle, R. Braun, S. Broadhurst, D. Brodrick, M. Brothers, A. Brown, J. D. Bunton, C. Cantrall, J. Chapman, W. Cheng, A. P. Chippendale, Y. Chung, F. Cooray, T. Cornwell, D. DeBoer, P. Diamond, P. G. Edwards, R. Ekers, I. Feain, R. H. Ferris, R. Forsyth, R. Gough, A. Grancea, N. Gupta, J. C. Guzman, G. Hampson, L. Harvey-Smith, C. Haskins, S. Hay, D. B. Hayman, I. Heywood, A. W. Hotan, S. Hoyle, B. Humphreys, B. T. Indermuehle, C. Jacka, C. Jackson, S. Jackson, K. Jeganathan, S. Johnston, J. Joseph, R. Kendall, M. Kesteven, D. Kiraly, S. B. Koribalski, M. Leach, E. Lenc, E. Lensson, S. Mackay, A. Macleod, M. Marquarding, J. Marvil, N. McClure-Griffiths, D. McConnell, P. Mirtschin, P. R. Norris, S. Neuhold, A. Ng, J. O'Sullivan, J. Pathikulangara, S. Pearce, C. Phillips, A. Popping, Y. R. Qiao, E. J. Reynolds, P. Roberts, J. R. Sault, A. Schinckel, P. Serra, R. Shaw, M. Shields, T. Shimwell, M. Storey, T. Sweetnam, E. Troup, B. Turner, J. Tuthill, A. Tzioumis, A. M. Voronkov, T. Westmeier, C. D. Wilson

*Corresponding author for this work

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    Abstract

    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 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 (tage ≈ 2500 yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of ~1 M o˙ yr-1.

    Original languageEnglish
    Pages (from-to)1249-1267
    Number of pages19
    JournalMonthly Notices of the Royal Astronomical Society
    Volume453
    Issue number2
    DOIs
    Publication statusPublished - 6 Aug 2015

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