Increasing AGN sample completeness using long-term near-infrared variability

Green, K; Elmer, E; Maltby, D T; Almaini, O; Merrifield, M; Hartley, W G

Abstract

In this work, we use 8 years of deep near-infrared imaging to select and study a new set of 601 active galaxies identified through long-term near-infrared (NIR) variability in the UKIDSS Ultra Deep Survey (UDS). These objects are compared to 710 X-ray bright AGN detected by the Chandra X-ray observatory. We show that infrared variability and X-ray emission select distinct sets of active galaxies, finding only a 37 per cent overlap of galaxies detected by both techniques and confirming NIR-variable AGN to be typically X-ray quiet. Examining the mass functions of the active galaxies shows that NIR variability detects AGN activity in galaxies over a significantly wider range of host stellar mass compared to X-ray detection. For example, at 𝑧 ∼ 1, variable AGN are identified among approximately 1 per cent of galaxies in a roughly flat distribution above the stellar mass completeness limit (> 109 M⊙ ), while X-ray detection primarily identifies AGN in galaxies of higher mass (> 1010 M⊙ ). We conclude that long-term near-infrared variability provides an important new tool for obtaining more complete samples of AGN in deep survey fields.

Citation

Green, K., Elmer, E., Maltby, D. T., Almaini, O., Merrifield, M., & Hartley, W. G. (2024). Increasing AGN sample completeness using long-term near-infrared variability. Monthly Notices of the Royal Astronomical Society, 531(2), 2551-2562. https://doi.org/10.1093/mnras/stae1322

• Journal Article Type: Article
• Acceptance Date: May 17, 2024
• Online Publication Date: May 23, 2024
• Publication Date: 2024-06
• Deposit Date: May 23, 2024
• Publicly Available Date: May 23, 2024
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 531
• Issue: 2
• Pages: 2551-2562
• DOI: https://doi.org/10.1093/mnras/stae1322
• Keywords: surveys, galaxies: active, galaxies: luminosity function, mass function, infrared: galaxies, X-rays: galaxies
• Public URL: https://nottingham-repository.worktribe.com/output/35153662
• Publisher URL: https://academic.oup.com/mnras/article/531/2/2551/7680582