Testing broad-line region models with reverberation mapping

Abstract

New reverberation mapping (RM) measurements, combined with accurate luminosities and line ratios, provide strong constraints on the location of the line emitting gas in the broad line region (BLR) of active galactic nuclei (AGN). In this paper I present new calculations of radiation pressure and magnetic pressure confined clouds and apply them to a "generic AGN" and to NGC 5548. The new calculations are in good agreement with the observed lags of all broad emission lines, and with the luminosities of Lyα, C iv 1549, O vi 1035 and He ii 1640. They are also in reasonable agreement with the luminosities of Mg ii 2798 and the 1990Å blend of C iii] and Siiii] lines for high metallicity gas. They explain the changes in time-lag following an increase in continuum luminosity and their dependencies on the inner and outer boundaries of the BLR. They also predict very strong Balmer and Paschen continua with important implications to continuum RM experiments. However, the calculated Balmer and Paschen line luminosities are too weak, by factors of 2-5. This "Balmer line crisis" was noted in several earlier works and is now confirmed and constrained by RM measurements that were not available in the past. It seems that present photoionization codes that use the escape probability formalism, fail to correctly compute the Balmer line luminosities in high density, large optical depth gas.

Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

“…This can be explained if emission from the “diffuse continuum” in the BLR is significant. The “diffuse continuum” (thermal free-bound and free-free, plus scattering) emanates from the same clouds that emit the broad emission lines ( Korista & Goad, 2001 , 2019 ; Lawther et al., 2018 ; Netzer, 2020 ). It is expected to contribute substantially to the continuum at all wavelengths but particularly around the Balmer (3646Å) and Paschen jumps (8204Å), as shown in Figure 7 .…”

“…There are a few limited, and notable, cases where the AGN is near enough and the black hole massive enough that the angular size is within reach of some methods. For instance, the Event Horizon Telescope used interferometry at sub-mm wavelengths to image the black hole shadow in M87 (Event Horizon Telescope Collaboration et al, 2019), and the GRAVITY interferometer on the Very Large Telescope (VLT) has also been able to resolve the BLR in 3C 273 and IRAS 09149-6206 (Gravity Collaboration et al, 2018, 2020. However, size scales of $ 10 5 R G are currently inaccessible to all but a few AGNs; in the future, X-ray interferometry may eventually make it possible to resolve scales of a few R G in the nearest Seyfert galaxies (Uttley et al, 2019).…”

Super

“…The objects are selected from the COSMOS-Legacy (e.g. Civano et al 2016, Suh et al 2015, 2020, the wide-area XMM-XXL (e.g. Georgakakis & Nandra 2011, Liu et al 2016, Menzel et al 2016), Stripe 82 X-ray survey (LaMassa et al 2016), and WISSH surveys (Bischetti et al 2017, Martocchia et al 2017, Duras et al 2017, Vietri et al 2018, and about 58% are Type-1 AGNs.…”

The spatially resolved broad line region of IRAS 09149−6206

“…For example, the Hα lag is expected to be larger than the Hβ lag due to radial stratification and optical depth effects (e.g. Rees et al 1989;Korista & Goad 2000Bottorff et al 2002;Netzer 2020). Zhang et al (2019) found the Hβ time lag of 3C 273 is fully consistent with the BLR radius measured by GRAVITY from the Paα 6 See Table 1 of Du & Wang (2019) for more details.…”