Publications

Discovery of HI gas in a young radio galaxy at z = 0.44 using the Australian Square Kilometre Array Pathfinder

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

We report the discovery of a new 21-cm H I 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 H I absorption at these redshifts. Optical spectroscopy and imaging using the Gemini-South telescope indicates that the H I gas is intrinsic to the host galaxy of the radio source. The narrow [O III] 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 H I 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 H I 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. We infer that the expanding young radio source (age ~ 2500 yr) is cocooned within a dense medium and may be driving circumnuclear neutral gas in an outflow of ~1 M_sun/yr.

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