An obscured quasar census with the 4MOST IR AGN survey: design, predicted properties, and scientific goals

Andonie, Carolina; Alexander, David M; Greenwell, Claire; Fotopoulou, Sotiria; Hickox, Ryan; Rosario, David J; Villforth, Carolin; Buchner, Johannes; Krogager, Jens-Kristian; Laloux, Brivael; Merloni, Andrea; Salvato, Mara; Streicher, Ole; Yan, Wei

Abstract

We present the 4MOST (4-metre Multi-Object Spectroscopic Telescope) infrared (IR) AGN survey, the first large-scale optical spectroscopic survey characterizing mid-infrared (MIR) selected obscured active galactic nuclei (AGNs). The survey targets obscured IR AGN candidates over down to a magnitude limit of and will be larger than any existing obscured IR AGN spectroscopic sample. We select the targets using an MIR colour criterion applied to the unWISE catalogue from the WISE (Wide-field Infrared Survey Explorer) all-sky survey, and then apply a cut; we demonstrate that this selection will mostly identify sources obscured by . The survey complements the 4MOST X-ray survey, which will follow up eROSITA (extended ROentgen Survey with an Imaging Telescope Array)-selected (typically unobscured) AGN. We perform simulations to predict the quality of the spectra that we will obtain and validate our MIR–optical colour-selection method using X-ray spectral constraints and UV-to-far-IR spectral energy distribution (SED) modelling in four well-observed deep-sky fields. We find that: (1) of the WISE-selected targets are AGN down to of which are obscured by , and (2) of the 4MOST IR AGN sample will remain undetected by the deepest eROSITA observations due to extreme absorption. Our SED-fitting results show that the 4MOST IR AGN survey will primarily identify obscured AGN and quasars ( of the sample is expected to have ) residing in massive galaxies () at with expected to be hosted by starburst galaxies.

Citation

Andonie, C., Alexander, D. M., Greenwell, C., Fotopoulou, S., Hickox, R., Rosario, D. J., Villforth, C., Buchner, J., Krogager, J.-K., Laloux, B., Merloni, A., Salvato, M., Streicher, O., & Yan, W. (2025). An obscured quasar census with the 4MOST IR AGN survey: design, predicted properties, and scientific goals. Monthly Notices of the Royal Astronomical Society, 539(3), 2202-2229. https://doi.org/10.1093/mnras/staf624

• Journal Article Type: Article
• Acceptance Date: Apr 10, 2025
• Online Publication Date: Apr 17, 2025
• Publication Date: 2025-05
• Deposit Date: May 20, 2025
• Publicly Available Date: May 20, 2025
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 539
• Issue: 3
• Pages: 2202-2229
• DOI: https://doi.org/10.1093/mnras/staf624
• Keywords: infrared: galaxies, surveys, quasars: general
• Public URL: https://durham-repository.worktribe.com/output/3942094