High radio-frequency properties and variability of brightest cluster galaxies
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 (≈1×10^(23) 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.
© 2015 The Royal Astronomical Society. Accepted 2015 July 7. Received 2015 May 23; in original form 2014 September 12. First published online August 25, 2015. We thank the anonymous referee for useful comments and suggestions that have greatly improved this work. MTH acknowledges the support of the Science and Technologies Funding Council (STFC) through studentship number ST/I505656/1. ACE acknowledges support from STFC grant ST/I001573/1. CR acknowledges the support of STFC. ACF and HRR acknowledge support from ERC Advanced Grant Feedback. We wish to thank the staff of the OVRO for allowing us access to data from their monitoring campaign and additional data for the sources they kindly added to the observing schedule. We would also like to thank the observatory staff at the MRAO (AMI), IRAM-30 m (GISMO), CARMA, the JCMT (SCUBA-2) and the GISMO team for their help in preparing and obtaining data. The OVRO 40-m monitoring programme is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. This research has made use of data from the UMRAO which has been supported by the University of Michigan and by a series of grants from the National Science Foundation, most recently AST-0607523. The James Clerk Maxwell Telescope is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the National Research Council of Canada and (until 2013 March 31) the Netherlands Organization for Scientific Research. Additional funds for the construction of SCUBA-2 were provided by the Canada Foundation for Innovation. Support for CARMA construction was derived from the states of California, Illinois and Maryland, the James S. McDonnell Foundation, the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the University of Chicago, the Associates of the California Institute of Technology and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement, and by the CARMA partner universities. The research leading to the IRAM-30 m results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement number 283393 (RadioNet3). This research work has used the TIFR GMRT Sky Survey (http://tgss.ncra.tifr.res.in) data products. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research used data from the NRAO archive. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Submitted - 1507.03022v1.pdf
Published - MNRAS-2015-Hogan-1223-40.pdf
Supplemental Material - Variability_Paper_Corrected.pdf