# Multiwavelength radio observations of a Brightest Cluster Galaxy at z=1.71: Detection of a modest Active Galactic Nucleus and evidence for extended star formation

## TL;DR

This study uses deep multiwavelength radio observations to analyze a high-redshift galaxy cluster's Brightest Cluster Galaxy, revealing a modest active nucleus and extended star formation possibly driven by multiple smaller galaxies or cooling flows.

## Contribution

First detailed multi-band radio study of a z=1.71 galaxy cluster's BCG, identifying a modest AGN and evidence for extended star formation beyond the galaxy itself.

## Key findings

- Detected a radio source with spectral index indicating an AGN.
- Radio fluxes are below star-forming SED predictions, suggesting extended or clumpy star formation.
- Star formation may be driven by multiple smaller galaxies or cooling flows, not a single merger.

## Abstract

We present deep, multiwavelength radio observations of SpARCS104922.6+564032.5, a z = 1.71 galaxy cluster with a starbusting core. Observations were made with the Karl G. Jansky Very Large Array (JVLA) in 3 bands: 1-2 GHz, 4-8 GHz and 8-12 GHz. We detect a radio source coincident with the Brightest Cluster Galaxy (BCG) that has a spectral index of {\alpha}=0.44\pm 0.29 and is indicative of emission from an Active Galactic Nucleus. The radio luminosity is consistent with the average luminosity of the lower redshift BCG sample, but the flux densities are 6{\sigma} below the predicted values of the star-forming Spectral Energy Distribution based on far infrared data. Our new fit fails to simultaneously describe the far infrared and radio fluxes. This, coupled with the fact that no other bright source is detected in the vicinity of the BCG implies that the star formation region, traced by the infrared emission, is extended or clumpy and not located directly within the BCG. Thus, we suggest that the star-forming core might not be driven by a single major wet merger, but rather by several smaller galaxies stripped of their gas or by a displaced cooling flow, although more data are needed to confirm any of those scenarios.