Identifying the first generation of radio powerful AGN in the Universe with the SKA

TL;DR

This paper explores how the SKA telescope can detect the earliest radio-loud AGN in the universe, focusing on overcoming observational challenges like CMB effects to study galaxy formation during reionisation.

Contribution

It analyzes SKA capabilities to optimize detection of high-redshift radio-loud AGN and proposes survey strategies to identify the first generation of such sources.

Findings

SKA can detect high-redshift radio-loud AGN despite CMB effects.

Optimal wavelength coverage and resolution are crucial for identifying early AGN.

Survey design can be tailored to maximize detection of the first radio-loud AGN.

Abstract

One of the most challenging and exciting subjects in modern astrophysics is that of galaxy formation at the epoch of reionisation. The SKA, with its revolutionary capabilities in terms of frequency range, resolution and sensitivity, will allow to explore the first Gyr of structure formation in the Universe, in particular, with the detection and study of the earliest manifestations of the AGN phenomenon. The tens of QSOs that are currently known out to the highest redshifts (z~7), many of them exhibiting powerful radio emission, imply that super-massive black holes can be grown on a very short timescale and support the existence of very high redshift (z > 7) radio loud sources - sources that have so far escaped detection. Not only would such detections be paramount to the understanding of the earliest stages of galaxy evolution, they are necessary for the direct study of neutral hydrogen in the Epoch of Reionisation, through observations of the HI 21cm forest against such background sources. In order to understand how SKA and SKA1 observations can be optimised to reveal these earliest AGN, we have examined the effect of a hot CMB on the emission of powerful and young radio galaxies. By looking at the SKA1 capabilities, in particular in terms of wavelength coverage and resolution, we determine how the effects of "CMB-muting" of a radio loud source can be observationally minimised and how to identify the best highest-redshift radio candidates. Considering different predictions for the space density of radio loud AGN at such redshifts, we identify the survey characteristics necessary to optimize the detection and identification of the very first generation of radio loud AGN in the Universe.