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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.

Ian Heywood

Visitor

Research theme

  • Astronomy and astrophysics

Sub department

  • Astrophysics

Research groups

  • Galaxy formation and evolution
  • MeerKAT
  • Pulsars, transients and relativistic astrophysics
  • The Square Kilometre Array (SKA)
  • Breakthrough Listen
ian.heywood@physics.ox.ac.uk
  • About
  • Publications

Evidence for inverse Compton scattering in high-redshift Lyman-break galaxies

Monthly Notices of the Royal Astronomical Society (2025) staf1505

Authors:

IH Whittam, MJ Jarvis, Eric J Murphy, NJ Adams, RAA Bowler, A Matthews, RG Varadaraj, CL Hale, I Heywood, K Knowles, L Marchetti, N Seymour, F Tabatabaei, AR Taylor, M Vaccari, A Verma

Abstract:

Radio continuum emission provides a unique opportunity to study star-formation unbiased by dust obscuration. However, if radio observations are to be used to accurately trace star-formation to high redshifts, it is crucial that the physical processes which affect the radio emission from star-forming galaxies are well understood. While inverse Compton (IC) losses from the cosmic microwave background (CMB) are negligible in the local universe, the rapid increase in the strength of the CMB energy density with redshift [∼(1 + z)4] means that this effect becomes increasingly important at z ≳ 3. Using a sample of ∼200, 000 high-redshift (3 < z < 5) Lyman-break galaxies selected in the rest-frame ultraviolet (UV), we have stacked radio observations from the MIGHTEE survey to estimate their 1.4-GHz flux densities. We find that for a given rest-frame UV magnitude, the 1.4-GHz flux density and luminosity decrease with redshift. We compare these results to the theoretical predicted effect of energy losses due to inverse Compton scattering off the CMB, and find that the observed decrease is consistent with this explanation. We discuss other possible causes for the observed decrease in radio flux density with redshift at a given UV magnitude, such as a top-heavy initial mass function at high redshift or an evolution of the dust properties, but suggest that inverse Compton scattering is the most compelling explanation.
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MIGHTEE: A first look at MIGHTEE quasars

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2025) staf1187

Authors:

Sarah V White, Ivan Delvecchio, Nathan Adams, Ian Heywood, Imogen H Whittam, Catherine L Hale, Neo Namane, Rebecca AA Bowler, Jordan D Collier

Abstract:

Abstract In this work we study a robust, Ks-band complete, spectroscopically-confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM-LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at 0.60 < zspec < 3.41. The quasars are selected via gJKs colour-space and, with 1.3-GHz flux-densities reaching rms ≈ 3.0 μ Jy beam−1, we find a radio-loudness fraction of 5percnt. Thanks to the deep, multiwavelength datasets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically-robust way, with the emphasis of this work being on the active-galactic-nuclei (AGN)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more-easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as ‘starbursts’. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.
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A MeerKAT survey of nearby dwarf novae: I. New detections

Monthly Notices of the Royal Astronomical Society Oxford University Press 539:3 (2025) 1894-1907

Authors:

J Kersten, E Körding, PA Woudt, PJ Groot, DRA Williams, I Heywood, DL Coppejans, C Knigge, JCA Miller-Jones, GR Sivakoff, R Fender

Abstract:

A programme to search for radio emission from dwarf-novae-type cataclysmic variables was conducted with the South African MeerKAT radio telescope. The dwarf novae RU Pegasi, V426 Ophiuchi, and IP Pegasi were detected during outburst at L band (1284 MHz central frequency). Previously, only one cataclysmic variable was radio-detected at a frequency this low. We now bring the number to four. With these three newly found radio-emitters, the population of dwarf novae confirmed to be radio-emitting at any frequency reaches 10 systems. We found that the radio luminosity is correlated with the optical luminosity. For V426 Ophiuchi and RU Pegasi we found a radio decline contemporary with the outburst’s optical decline. The peak radio luminosity of dwarf novae in outburst is very similar to that of novalike Cataclysmic Variables and no correlation with orbital period is seen.
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Non-thermal filaments and AGN recurrent activity in the galaxy group Nest200047: A LOFAR, uGMRT, MeerKAT, and VLA radio spectral analysis

Astronomy & Astrophysics EDP Sciences 696 (2025) a239

Authors:

M Brienza, K Rajpurohit, E Churazov, I Heywood, M Brüggen, M Hoeft, F Vazza, A Bonafede, A Botteon, G Brunetti, F Gastaldello, I Khabibullin, N Lyskova, A Majumder, HJA Röttgering, TW Shimwell, A Simionescu, RJ van Weeren
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The jet paths of radio active galactic nuclei and their cluster weather

Astronomy & Astrophysics EDP Sciences 695 (2025) a178

Authors:

E Vardoulaki, V Backöfer, A Finoguenov, F Vazza, J Comparat, G Gozaliasl, IH Whittam, CL Hale, JR Weaver, AM Koekemoer, JD Collier, B Frank, I Heywood, S Sekhar, AR Taylor, S Pinjarkar, MJ Hardcastle, T Shimwell, M Hoeft, SV White, F An, F Tabatabaei, Z Randriamanakoto, MD Filipovic
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