Infrared lags in the light curves of AGN measured using a deep survey

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

Abstract

Information on the structure around active galactic nuclei (AGNs) has long been derived from measuring lags in their varying light output at different wavelengths. In principle, infrared data would reach to larger radii, potentially even probing reprocessed radiation in any surrounding dusty torus. In practice, this has proved challenging because high quality data are required to detect such variability, and the observations must stretch over a long period to probe the likely month-scale lags in variability. In addition, large numbers of sources would need to be observed to start searching for any patterns in such lags. Here, we show that the UKIDSS Ultra Deep Survey, built up from repeated observations over almost a decade, provides an ideal data set for such a study. For 94 sources identified as strongly varying AGNs within its square-degree field, we find that the K-band light curves systematically lag the J-band light curves by an average of around a month. The lags become smaller at higher redshift, consistent with the band shift to optical rest-frame emission. The less luminous AGNs also display shorter lags, as would be expected if their physical size scales with luminosity.

Citation

Elmer, E., Merrifield, M., Almaini, O., Hartley, W. G., & Maltby, D. T. (2021). Infrared lags in the light curves of AGN measured using a deep survey. Monthly Notices of the Royal Astronomical Society: Letters, 503(1), L47-L50. https://doi.org/10.1093/mnrasl/slab023

• Journal Article Type: Article
• Acceptance Date: Feb 26, 2021
• Online Publication Date: Mar 8, 2021
• Publication Date: 2021-05
• Deposit Date: Jun 7, 2021
• Publicly Available Date: Jun 18, 2021
• Journal: Monthly Notices of the Royal Astronomical Society: Letters
• Electronic ISSN: 1745-3933
• Publisher: Oxford University Press (OUP)
• Peer Reviewed: Peer Reviewed
• Volume: 503
• Issue: 1
• Pages: L47-L50
• DOI: https://doi.org/10.1093/mnrasl/slab023
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/5394772
• Publisher URL: https://academic.oup.com/mnrasl/article/503/1/L47/6162634
• Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters ©: 2021The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.