The SOUX AGN sample: optical/UV/X-ray SEDs and the nature of the disc

0574938 - ASÚ 2024 RIV US eng J - Journal Article
Mitchell, J. A. J. - Done, C. - Ward, M. J. - Kynoch, Daniel - Hagen, S. - Lusso, E. - Landt, H.
The SOUX AGN sample: optical/UV/X-ray SEDs and the nature of the disc.
Monthly Notices of the Royal Astronomical Society. Roč. 524, č. 2 (2023), s. 1796-1825. ISSN 0035-8711. E-ISSN 1365-2966
R&D Projects: GA ČR(CZ) GJ19-05599Y
Institutional support: RVO:67985815
Keywords : accretion discs * black hole physics * active galaxies
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 4.8, year: 2022
Method of publishing: Open access

We use the SOUX sample of & SIM, 700 active galactic nucleus (AGN) to form average optical-ultraviolet (UV)-X-rays spectral energy distributions (SEDs) on a two-dimensional (2D) grid of M-BH and L-2500. We compare these with the predictions of a new AGN SED model, qsosed, which includes prescriptions for both hot and warm Comptonization regions as well as an outer standard disc. This predicts the overall SED fairly well for 7.5 < log(M-BH/M-& ODOT) < 9.0 over a wide range in L/L-Edd, but at higher masses the outer disc spectra in the model are far too cool to match the data. We create optical-UV composites from the entire Sloan Digital Sky Survey sample and use these to show that the mismatch is due to there being no significant change in spectral shape of the optical-UV continuum across several decades of M-BH at constant luminosity. We show for the first time that this cannot be matched by standard disc models with high black hole spin. These apparently fit, but are not self-consistent as they do not include the General Relativistic effects for the emission to reach the observer. At high spin, increased gravitational redshift compensates for almost all of the higher temperature emission from the smaller inner disc radii. The data do not match the predictions made by any current accretion flow model. Either the disc is completely covered by a warm Comptonization layer whose properties change systematically with L/L-Edd, or the accretion flow structure is fundamentally different to that of the standard disc models.
Permanent Link: https://hdl.handle.net/11104/0345208