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High radio-frequency properties and variability of brightest cluster galaxies.

Hogan, M.T. and Edge, A.C. and Geach, J.E. and Grainge, K.J.B. and Hlavacek-Larrondo, J. and Hovatta, T. and Karim, A. and McNamara, B.R. and Rumsey, C. and Russell, H.R. and Salomé, P. and Aller, H.D. and Aller, M.F. and Benford, D.J. and Fabian, A.C. and Readhead, A.C.S. and Sadler, E.M. and Saunders, R.D.E. (2015) 'High radio-frequency properties and variability of brightest cluster galaxies.', Monthly notices of the Royal Astronomical Society., 453 (2). pp. 1223-1240.


We consider the high radio-frequency (15–353 GHz) properties and variability of 35 brightest cluster galaxies (BCGs). These are the most core-dominated sources drawn from a parent sample of more than 700 X-ray selected clusters, thus allowing us to relate our results to the general population. We find that ≥6.0 per cent of our parent sample (≥15.1 per cent if only cool-core clusters are considered) contain a radio source at 150 GHz of at least 3 mJy (≈1×1023 W Hz−1 at our median redshift of z ≈ 0.13). Furthermore, ≥3.4 per cent of the BCGs in our parent sample contain a peaked component (Gigahertz Peaked Spectrum, GPS) in their spectra that peaks above 2 GHz, increasing to ≥8.5 per cent if only cool-core clusters are considered. We see little evidence for strong variability at 15 GHz on short (week–month) time-scales although we see variations greater than 20 per cent at 150 GHz over six-month time frames for 4 of the 23 sources with multi-epoch observations. Much more prevalent is long-term (year–decade time-scale) variability, with average annual amplitude variations greater than 1 per cent at 15 GHz being commonplace. There is a weak trend towards higher variability as the peak of the GPS-like component occurs at higher frequency. We demonstrate the complexity that is seen in the radio spectra of BCGs and discuss the potentially significant implications of these high-peaking components for Sunyaev–Zel‘dovich cluster searches.

Item Type:Article
Keywords:Galaxies: active, Galaxies: clusters: general, Galaxies: jets, Radio continuum: galaxies.
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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:07 July 2015
Date deposited:05 November 2015
Date of first online publication:October 2015
Date first made open access:No date available

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