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Black Hole

Lensing of space time around a black hole. At Oxford we study black holes observationally and theoretically on all size and time scales - it is some of our core work.

Credit: ALAIN RIAZUELO, IAP/UPMC/CNRS. CLICK HERE TO VIEW MORE IMAGES.

Dr James Allison

CDF (Christ Church)

Research theme

  • Astronomy and astrophysics

Sub department

  • Astrophysics

Research groups

  • Galaxy formation and evolution
  • Hintze Centre for Astrophysical Surveys
  • MeerKAT
james.allison@physics.ox.ac.uk
Christ Church webpage
  • About
  • Teaching
  • Research
  • Publications

Further observational evidence for a critical ionizing luminosity in active galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 470:4 (2017) 4600-4607

Authors:

SJ Curran, RW Hunstead, HM Johnston, MT Whiting, EM Sadler, JR Allison, C Bignell
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Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN

Monthly Notices of the Royal Astronomical Society Oxford University Press 471:3 (2017) 2952-2973

Authors:

VA Moss, Allison, EM Sadler, R Urquhart, R Soria, Callingham, SJ Curran, A Musaeva, EK Mahony, M Glowacki, Farrell, KW Bannister, AP Chippendale, PG Edwards, L Harvey-Smith, Ian Heywood, AW Hotan, BT Indermuehle, E Lenc, J Marvil, D McConnell, JE Reynolds, MA Voronkov, RM Wark, MT Whiting

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.
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Atomic and molecular absorption in redshifted radio sources

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 467:4 (2017) 4514-4525

Authors:

SJ Curran, MT Whiting, JR Allison, A Tanna, EM Sadler, R Athreya
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The Detection of an Extremely Bright Fast Radio Burst in a Phased Array Feed Survey

The Astrophysical Journal American Astronomical Society 841:1 (2017) L12-L12

Authors:

KW Bannister, RM Shannon, J-P Macquart, C Flynn, PG Edwards, M O’Neill, S Osłowski, M Bailes, B Zackay, N Clarke, LR D’Addario, R Dodson, PJ Hall, A Jameson, D Jones, R Navarro, JT Trinh, J Allison, CS Anderson, M Bell, AP Chippendale, JD Collier, G Heald, I Heywood, AW Hotan, K Lee-Waddell, JP Madrid, J Marvil, D McConnell, A Popping, MA Voronkov, MT Whiting, GR Allen, DC-J Bock, DP Brodrick, F Cooray, DR DeBoer, PJ Diamond, R Ekers, RG Gough, GA Hampson, L Harvey-Smith, SG Hay, DB Hayman, CA Jackson, S Johnston, BS Koribalski, NM McClure-Griffiths, P Mirtschin, A Ng, RP Norris, SE Pearce, CJ Phillips, DN Roxby, ER Troup, T Westmeier
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Delayed triggering of radio active galactic nuclei in gas-rich minor mergers in the local Universe

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 464:4 (2017) 4706-4720

Authors:

SS Shabala, A Deller, S Kaviraj, E Middelberg, RJ Turner, YS Ting, JR Allison, TA Davis
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