High Radio Frequency Properties and Variability of Brightest Cluster Galaxies

TL;DR

This study investigates the high-frequency radio properties and variability of Brightest Cluster Galaxies, revealing their spectral complexity and implications for cluster detection methods.

Contribution

It provides the first comprehensive analysis of high-frequency radio spectra and variability of BCGs, highlighting the prevalence of peaked components and their impact on Sunyaev-Zel'dovich surveys.

Findings

Over 6% of the sample have radio sources at 150 GHz with flux >3mJy

More than 3.4% contain a GPS component peaking above 2 GHz

Long-term variability is common, with >1% annual amplitude changes at 15 GHz

Abstract

We consider the high radio frequency (15 GHz - 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% of our parent sample (>15.1% if only cool-core clusters are considered) contain a radio-source at 150 GHz of at least 3mJy (~1x10^23 W/Hz at our median redshift of z~0.13). Furthermore, >3.4% 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% 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% at 150 GHz over 6-month times-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% 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.