Ian Heywood: Publications

A unique, ring-like radio source with quadrilateral structure detected with machine learning

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2023)

Authors:

M Lochner, L Rudnick, I Heywood, K Knowles, SS Shabala

Abstract:

Abstract We report the discovery of a unique object in the MeerKAT Galaxy Cluster Legacy Survey (MGCLS) using the machine learning anomaly detection framework Astronomaly. This strange, ring-like source is 30′ from the MGCLS field centred on Abell 209, and is not readily explained by simple physical models. With an assumed host galaxy at redshift 0.55, the luminosity (1025 W Hz−1) is comparable to powerful radio galaxies. The source consists of a ring of emission 175 kpc across, quadrilateral enhanced brightness regions bearing resemblance to radio jets, two “ears” separated by 368 kpc, and a diffuse envelope. All of the structures appear spectrally steep, ranging from -1.0 to -1.5. The ring has high polarization (25%) except on the bright patches (<10%). We compare this source to the Odd Radio Circles recently discovered in ASKAP data and discuss several possible physical models, including a termination shock from starburst activity, an end-on radio galaxy, and a supermassive black hole merger event. No simple model can easily explain the observed structure of the source. This work, as well as other recent discoveries, demonstrates the power of unsupervised machine learning in mining large datasets for scientifically interesting sources.

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MeerKAT follow-up of enigmatic GLEAM 4-Jy (G4Jy) sources

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 518:3 (2023) 4290-4309

Authors:

Precious K Sejake, Sarah V White, Ian Heywood, Kshitij Thorat, Hertzog L Bester, Sphesihle Makhathini, Bernie Fanaroff

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MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star forming galaxies and active galactic nuclei

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2022)

Authors:

CL Hale, IH Whittam, MJ Jarvis, PN Best, NL Thomas, I Heywood, M Prescott, N Adams, J Afonso, Fangxia An, RAA Bowler, JD Collier, RHW Cook, R Davé, BS Frank, M Glowacki, PW Hatfield, S Kolwa, CC Lovell, N Maddox, L Marchetti, LK Morabito, E Murphy, I Prandoni, Z Randriamanakoto, AR Taylor

Abstract:

Abstract We present deep 1.4 GHz source counts from ∼5 deg2 of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to S1.4GHz ∼15 μJy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25 per cent contribution to the total sky background temperature (Tb ∼100 mK) at ∼15 μJy.

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MIGHTEE: the nature of the radio-loud AGN population

Monthly Notices of the Royal Astronomical Society Oxford University Press 516:1 (2022) 245-263

Authors:

Ih Whittam, Mj Jarvis, Cl Hale, M Prescott, Lk Morabito, I Heywood, Nj Adams, J Afonso, Fangxia An, Y Ao, Raa Bowler, Jd Collier, J Delhaize, B Frank, M Glowacki, Pw Hatfield, N Maddox, L Marchetti, Am Matthews, S Randriamampandry, Z Randriamanakoto, Djb Smith, Ar Taylor, Nl Thomas, M Vaccari

Abstract:

We study the nature of the faint radio source population detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Early Science data in the COSMOS field, focusing on the properties of the radio-loud active galactic nuclei (AGNs). Using the extensive multiwavelength data available in the field, we are able to classify 88 per cent of the 5223 radio sources in the field with host galaxy identifications as AGNs (35 per cent) or star-forming galaxies (54 per cent). We select a sample of radio-loud AGNs with redshifts out to z ∼ 6 and radio luminosities 10²⁰ < L_1.4 GHz/W Hz⁻¹ < 10²⁷ and classify them as high-excitation and low-excitation radio galaxies (HERGs and LERGs). The classification catalogue is released with this work. We find no significant difference in the host galaxy properties of the HERGs and LERGs in our sample. In contrast to previous work, we find that the HERGs and LERGs have very similar Eddington-scaled accretion rates; in particular we identify a population of very slowly accreting AGNs that are formally classified as HERGs at these low radio luminosities, where separating into HERGs and LERGs possibly becomes redundant. We investigate how black hole mass affects jet power, and find that a black hole mass ≳ 10^7.8 M_⊙ is required to power a jet with mechanical power greater than the radiative luminosity of the AGN (L_mech/L_bol > 1). We discuss that both a high black hole mass and black hole spin may be necessary to launch and sustain a dominant radio jet.

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A MeerKAT, e-MERLIN, HESS, and Swift search for persistent and transient emission associated with three localized FRBs

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 515:1 (2022) 1365-1379

Authors:

JO Chibueze, M Caleb, L Spitler, H Ashkar, F Schussler, BW Stappers, C Venter, I Heywood, AMS Richards, DRA Williams, M Kramer, R Beswick, MC Bezuidenhout, RP Breton, LN Driessen, F Jankowski, EF Keane, M Malenta, M Mickaliger, V Morello, H Qiu, K Rajwade, S Sanidas, M Surnis, TW Scragg, CRH Walker, N Wrigley, F Aharonian, F Ait Benkhali, EO Anguener, M Backes, V Baghmanyan, V Barbosa Martins, R Batzofin, Y Becherini, D Berge, M Bottcher, C Boisson, J Bolmont, M de Bony de Lavergne, M Breuhaus, R Brose, F Brun, T Bulik, F Cangemi, S Caroff, S Casanova, J Catalano, M Cerruti, T Chand, A Chen, OU Chibueze, G Cotter, P Cristofari, J Damascene Mbarubucyeye, J Devin, A Djannati-Atai, A Dmytriiev, K Egberts, J-P Ernenwein, A Fiasson, G Fichet de Clairfontaine, G Fontaine, S Funk, S Gabici, S Ghafourizadeh, G Giavitto, D Glawion, M-H Grondin, M Horbe, C Hoischen, TL Holch, Zhiqiu Huang, M Jamrozy, F Jankowsky, V Joshi, I Jung-Richardt, E Kasai, K Katarzynski, U Katz, B Khelifi, W Kluzniak, Nu Komin, K Kosack, D Kostunin, A Lemiere, J-P Lenain, F Leuschner, T Lohse, A Luashvili, I Lypova, J Mackey, D Malyshev, V Marandon, P Marchegiani, A Marcowith, G Marti-Devesa, R Marx, A Mitchell, R Moderski, L Mohrmann, E Moulin, J Muller, K Nakashima, M de Naurois, A Nayerhoda, J Niemiec, A Priyana Noel, P O'Brien, S Ohm, L Olivera-Nieto, E de Ona Wilhelmi, M Ostrowski, S Panny, RD Parsons, S Pita, V Poireau, DA Prokhorov, H Prokoph, G Puehlhofer, A Quirrenbach, P Reichherzer, A Reimer, O Reimer, G Rowell, B Rudak, E Ruiz-Velasco, V Sahakian, S Sailer, H Salzmann, DA Sanchez, A Santangelo, M Sasaki, HM Schutte, U Schwanke, JNS Shapopi, A Specovius, S Spencer, R Steenkamp, S Steinmassl, T Takahashi, T Tanaka, C Thorpe-Morgan, N Tsuji, C van Eldik, J Veh, J Vink, SJ Wagner, A Wierzcholska, Yu Wun Wong, A Yusafzai, M Zacharias, D Zargaryan, AA Zdziarski, A Zech, SJ Zhu, S Zouari, N Zywucka, HESS Collaboration

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Ian Heywood

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A unique, ring-like radio source with quadrilateral structure detected with machine learning

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MeerKAT follow-up of enigmatic GLEAM 4-Jy (G4Jy) sources

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MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star forming galaxies and active galactic nuclei

Authors:

Abstract:

MIGHTEE: the nature of the radio-loud AGN population

Authors:

Abstract:

A MeerKAT, e-MERLIN, HESS, and Swift search for persistent and transient emission associated with three localized FRBs

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Ian Heywood

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A unique, ring-like radio source with quadrilateral structure detected with machine learning

Authors:

Abstract:

MeerKAT follow-up of enigmatic GLEAM 4-Jy (G4Jy) sources

Authors:

MIGHTEE: deep 1.4 GHz source counts and the sky temperature contribution of star forming galaxies and active galactic nuclei

Authors:

Abstract:

MIGHTEE: the nature of the radio-loud AGN population

Authors:

Abstract:

A MeerKAT, e-MERLIN, HESS, and Swift search for persistent and transient emission associated with three localized FRBs

Authors: