4MOST Consortium Survey 6: Active Galactic Nuclei

TL;DR

This paper outlines a large spectroscopic survey using 4MOST to identify and study active galactic nuclei across a significant portion of the sky, aiming to understand their properties, evolution, and role in galaxy development.

Contribution

It introduces a systematic approach to follow up X-ray and mid-infrared selected AGN, achieving high completeness and enabling detailed analysis of supermassive black holes up to redshift 6.

Findings

Achieves 80-90% completeness for X-ray selected AGN with fluxes > 10^-14 erg s^-1 cm^-2

Will determine physical properties of up to one million supermassive black holes

Constrains cosmic evolution and clustering of AGN across redshifts 0 to 6

Abstract

X-ray and mid-infrared emission are signposts of the accretion of matter onto the supermassive black holes that reside at the centres of most galaxies. As a major step towards understanding accreting supermassive black holes and their role in the evolution of galaxies, we will use the 4MOST multi-object spectrograph to provide a highly complete census of active galactic nuclei over a large fraction of the extragalactic sky observed in X-rays by eROSITA that is visible to 4MOST. We will systematically follow up all eROSITA point-like extragalactic X-ray sources (mostly active galactic nuclei), and complement them with a heavily obscured active galactic nuclei selection approach using mid-infrared data from the Wide-field Infrared Survey Explorer (WISE). The X-ray and mid-infrared flux limits of eROSITA and WISE are well matched to the spectroscopic capabilities of a 4-metre-class telescope, allowing us to reach completeness levels of ~80-90% for all X-ray selected active galactic nuclei with fluxes $f_{0.5-2\ {\rm keV}} > 10^{-14}$ erg s$^{-1}$ cm$^{-2}$; this is about a factor of 30 deeper than the ROSAT all-sky survey. With these data we will determine the physical properties (redshift, luminosity, line emission strength, masses, etc.) of up to one million supermassive black holes, constrain their cosmic evolution and clustering properties, and explore the connection between active galactic nuclei and large-scale structure over redshifts $0 \le z \le 6$.