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The mean reddening of the continuum and broad-line region of NGC 5548: implications for the size of the accretion disk

Presentation #101.27 in the session AGN & Quasars — iPoster Session.

Published onJun 29, 2022
The mean reddening of the continuum and broad-line region of NGC 5548: implications for the size of the accretion disk

We use seven different methods to estimate broad-line and continuum reddenings of NGC~5548. We consider two possible reddening curves considered for active galactic nuclei (AGNs): a curve that rises strongly into the ultraviolet like the curve for the Small Magellanic Cloud, and the mean AGN reddening curve of Gaskell & Benker (2007), which is much flatter in the ultraviolet. We also consider a standard Milky Way curve. Regardless of the curve adopted, we find a total reddening ~ 10–15 times greater than the small amount of reddening due to dust in the solar neighborhood. The UV-to-optical ratios rule out a steep SMC-like reddening curve for NGC 5548. The Milky Way and Gaskell & Benker curves give a mean reddening of E(B-V) = 0.26 ± 0.03. The four non-hydrogen-line reddening indicators imply that the intrinsic hydrogen line ratios are consistent with Menzel-Baker case B values. The mean reddening we derive for NGC 5548 is typical of previous estimates for type-1 AGNs. Neglecting internal extinction leads to an underestimate of the luminosity below 1200 Angstroms by a factor of about ten. The size scale of the accretion disc has therefore been underestimated by a factor of 2.6. This is similar to the accretion disc size discrepancy found in the 2013 AGNSTORM campaign and thus supports the proposal by Gaskell (2017) that the size discrepancy is primarily due to the neglect of reddening.

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