High radio-frequency properties and variability of brightest cluster galaxies

M.~T. Hogan, A.~C. Edge, J.~E. Geach, K.~J.~B. Grainge, J. Hlavacek-Larrondo, T. Hovatta, A. Karim, B.~R. McNamara, C. Rumsey, H.~R. Russell, P. Salomé, H.~D. Aller, M.~F. Aller, D.~J. Benford, A.~C. Fabian, A.~C.~S. Readhead, E.~M. Sadler, R.~D.~E. Saunders

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Abstract

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.
Original languageEnglish
Pages (from-to)1223-1240
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Volume453
Issue number2
Early online date24 Aug 2015
DOIs
Publication statusPublished - 21 Oct 2015

Keywords

  • galaxies: active, galaxies: clusters: general, galaxies: jets, radio continuum: galaxies

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