Non-thermal Sunyaev-Zeldovich signal from radio galaxy lobes

TL;DR

This paper models the non-thermal Sunyaev-Zeldovich effect from radio galaxy lobes, showing it can be significant in galaxy clusters and discussing how future CMB observations could detect this signal.

Contribution

It introduces an improved evolutionary model for radio galaxy lobes to estimate non-thermal SZ effects and explores physical parameter effects on observability.

Findings

Non-thermal SZ distortions can be comparable to thermal SZ in galaxy clusters.

Young, small radio galaxies in clusters are promising for detecting non-thermal SZ signals.

Constraints on electron spectrum low-energy cut-off from recent SZ detections.

Abstract

Energetic electrons in the lobes of radio galaxies make them potential sources for not only radio and X-rays but also Sunyaev-Zeldovich (SZ) distortions in the cosmic microwave background (CMB) radiation. Previous works have discussed the energetics of radio galaxy lobes, but assuming thermal SZ effect, coming from the non-thermal electron population. We use an improved evolutionary model for radio galaxy lobes to estimate the observed parameters such as the radio luminosity and intensity of SZ-distortions at the redshifts of observation. We, further, quantify the effects of various relevant physical parameters of the radio galaxies, such as the jet power, the time scale over which the jet is active, the evolutionary time scale for the lobe, etc on the observed parameters. For current SZ observations towards galaxy clusters, we find that the non-thermal SZ distortions from radio lobes embedded in galaxy clusters can be non-negligible compared to the amount of thermal SZ distortion from the intra-cluster medium and, hence, can not be neglected. We show that small and young (and preferably residing in a cluster environment) radio galaxies offer better prospects for the detection of the non-thermal SZ signal from these sources. We further discuss the limits on different physical parameters for some sources for which SZ effect has been either detected or upper limits are available. The evolutionary models enable us to obtain limits, previously unavailable, on the low energy cut-off of electron spectrum ($p_{min} \sim 1\hbox{--}2$) in order to explain the recent non-thermal SZ detection. Finally, we discuss how future CMB experiments, which would cover higher frequency bands ($>$400 GHz), may provide clear signatures for non-thermal SZ effect.