Discovery of H I gas in a young radio galaxy at z = 0.44 using the Australian Square Kilometre Array Pathfinder
Forsyth, R.; Sault, R. J.; Heywood, I.; Wilson, C. D.; Braun, R.; Johnston, S.; Morganti, R.; Edwards, P. G.; Ball, L.; Zwaan, M. A.; Norris, R. P.; Koribalski, B. S.; McConnell, D.; Croom, S. M.; Sadler, E. M.; Feain, I.; Westmeier, T.; Serra, P.; Glowacki, M.; Shimwell, T.; Hunstead, R. W.; Brown, A.; Marvil, J.; Bell, M. E.; Lenc, E.; Harvey-Smith, L.; Gupta, N.; Tzioumis, A.; Reynolds, J. E.; Shields, M.; Boyle, B.; Allison, J. R.; Moss, V. A.; Whiting, M. T.; Pracy, M. B.; Curran, S. J.; Shabala, S. S.; Allen, G.; Amy, S. W.; Axtens, P.; Bannister, K. W.; Barker, S.; Bock, D. C. -J.; Bolton, R.; Bowen, M.; Broadhurst, S.; Brodrick, D.; Brothers, M.; Bunton, J. D.; Cantrall, C.; Chapman, J.; Cheng, W.; Chippendale, A. P.; Chung, Y.; Cooray, F.; Cornwell, T.; DeBoer, D.; Diamond, P.; Ekers, R.; Ferris, R. H.; Gough, R.; Grancea, A.; Guzman, J. C.; Hampson, G.; Haskins, C.; Hay, S.; Hayman, D. B.; Hotan, A. W.; Hoyle, S.; Humphreys, B.; Indermuehle, B. T.; Jacka, C.; Jackson, C.; Jackson, S.; Jeganathan, K.; Joseph, J.; Kendall, R.; Kesteven, M.; Kiraly, D.; Leach, M.; Lensson, E.; Mackay, S.; Macleod, A.; Marquarding, M.; McClure-Griffiths, N.; Mirtschin, P.; Neuhold, S.; Ng, A.; O'Sullivan, J.; Pathikulangara, J.; Pearce, S.; Phillips, C.; Popping, A.; Qiao, R. Y.; Roberts, P.; Schinckel, A.; Shaw, R.; Storey, M.; Sweetnam, T.; Troup, E.; Turner, B.; Tuthill, J.; Voronkov, M. A.
Australia, New Zealand, Netherlands, Germany, United Kingdom, United States, India, South Africa
Abstract
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-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⊙ yr-1.