Systematic collapse of the accretion disc in AGN confirmed by UV photometry and broad-line spectra

Kang, Jia Lai; Done, Chris; Hagen, Scott; Temple, Matthew J.; Silverman, John D.; Li, Junyao; Liu, Teng

Abstract

A recent study on the spectral energy distribution (SED) of active galactic nuclei (AGNs) combined unobscured X-ray sources from the eROSITA eFEDS Survey with high quality optical imaging from Subaru’s Hyper Suprime-Cam (HSC). The HSC data enabled accurate host galaxy subtraction as well as giving a uniform black hole mass estimator from the stellar mass. The resulting stacked optical/X-ray SEDs for black holes at fixed mass show a dramatic transition, where the dominating disc component in bright AGN evaporates into an X-ray hot plasma below L/LEdd ∼ 0.01. The models fit to these data sets predicted the largest change in SED in the rest frame UV (< 3000 Å), but this waveband was not included in the original study. Here we use archival u-band and UV photometry to extend the SEDs into this range, and confirm the UV is indeed intrinsically faint in AGN below L/LEdd ∼ 0.01 as predicted. This dramatic drop in UV photoionizing flux is also seen from its effect on the broad emission lines. We stack the recently released SDSS DR18 optical spectra for this sample, and show that the broad Hβ line disappears along with the UV bright component at L/LEdd ∼ 0.01. This shows that there is a population of unobscured, X-ray bright, UV faint AGN which lack broad emission lines (true type 2 Seyferts).

Citation

Kang, J. L., Done, C., Hagen, S., Temple, M. J., Silverman, J. D., Li, J., & Liu, T. (2025). Systematic collapse of the accretion disc in AGN confirmed by UV photometry and broad-line spectra. Monthly Notices of the Royal Astronomical Society, 538(1), 121-131. https://doi.org/10.1093/mnras/staf145

• Journal Article Type: Article
• Acceptance Date: Jan 21, 2024
• Online Publication Date: Feb 27, 2025
• Publication Date: Mar 1, 2025
• Deposit Date: Apr 7, 2025
• Publicly Available Date: Apr 7, 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: 538
• Issue: 1
• Pages: 121-131
• DOI: https://doi.org/10.1093/mnras/staf145
• Public URL: https://durham-repository.worktribe.com/output/3781946