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  • Connecting X-ray absorption...
    Moss, V. A; Allison, J. R; Sadler, E. M; Urquhart, R; Soria, R; Callingham, J.R; Curran, S. J; Musaeva, A; Mahony, E. K; Glowacki, M; Farrell, S. A; Bannister, K. W; Chippendale, A. P; Edwards, P. G; Harvey-Smith, L; Heywood, I; Hotan, A. W; Indermuehle, B. T; Lenc, E; Marvil, J; McConnell, D; Reynolds, J. E; Voronkov, M. A; Wark, R. M; Whiting, M. T

    Monthly Notices of the Royal Astronomical Society, 11/2017, Volume: 471, Issue: 3
    Journal Article

    Abstract Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21 cm H i absorption and soft X-ray absorption, offering new insight into the physical nature of the circumnuclear medium of these distant galaxies. To better understand this relationship, we investigate soft X-ray absorption as an indicator for the detection of associated H i absorption, as part of preparation for the First Large Absorption Survey in H i to be undertaken with the Australian Square Kilometre Array Pathfinder (ASKAP). We present the results of our pilot study using the Boolardy Engineering Test Array, a precursor to ASKAP, to search for new absorption detections in radio sources brighter than 1 Jy that also feature soft X-ray absorption. Based on this pilot survey, we detected H i absorption towards the radio source PKS 1657−298 at a redshift of z = 0.42. This source also features the highest X-ray absorption ratio of our pilot sample by a factor of 3, which is consistent with our general findings that X-ray absorption predicates the presence of dense neutral gas. By comparing the X-ray properties of active galactic nuclei with and without detection of H i absorption at radio wavelengths, we find that X-ray hardness ratio and H i absorption optical depth are correlated at a statistical significance of 4.71σ. We conclude by considering the impact of these findings on future radio and X-ray absorption studies.