CLOUDY View of the Warm Corona

Abstract

Bright active galaxies show a range of properties but many of these properties are correlated which has led to the concept of the Quasar Main Sequence. We test whether our current understanding of the quasar structure allows to reproduce the pattern observed in the optical plane formed by the kinematic line width of Hβ and the relative importance of the Fe II optical emission. We performed simulations of the Hβ and Fe II production using the code CLOUDY and well justified assumptions about the broad band spectra, distance of the emission line region, and the cloud properties. We show that the presence of the warm corona is an important element of the broad band spectrum which decreases the dependence of the relative Fe II emissivity on the Eddington ratio, and allows to reproduce the rare cases of the particularly strong Fe II emitters. Results are sensitive to the adopted cloud distance, and strong Fe II emission can be obtain either by adopting strongly super-solar metallicity, or much shorter distance than traditionally obtained from reverberation mapping. We modeled in a similar way the UV plane defined by the Mg II line and Fe II UV pseudo-continuum, but here our approach is less successful, in general overproducing the Fe II strength. We found that the Fe II optical and UV emissivity depend in a different way on the turbulent velocity and metallicity, and the best extension of the model in order to cover both planes is to allow very large turbulent velocities in the Broad Line Region clouds.

Radiation spectra of warm and optically thick coronae in AGNs

“…It is already known that a warm corona can stabilize the underlying accretion disk, otherwise subject to radiation pressure instability (see Czerny 2019 for a very recent review). More unexpectedly, the presence of a warm corona in the quasar spectral energy distribution have been recently shown to be an important element to reproduce the extreme part of the "main sequence" of quasars 5 , especially quasars with particularly strong FeII emission (Panda et al, 2019). These two examples show already the wide variety of impacts expected from the existence of such a warm corona in the inner regions of AGN.…”

Bolometric correction factors for active galactic nuclei

“…In particular, two or three-part disks involving warm and hot X-ray gas, have been suggested (e.g. Done et al 2012;Kubota & Done 2018;Panda et al 2019, and references therein). Such systems produce significantly different ionizing SEDs and are discussed, briefly, in §2.2.…”

Main trends of the quasar main sequence - effect of viewing angle

“…The use of angle-dependent form factor (see Eq. 2 and 5) is a crucial extension of the quasar MS modelling done by Panda et al (2017Panda et al ( , 2018Panda et al ( , 2019a. Viewing angle directly affects the line width, and the object luminosity, and indirectly the estimated distance to the BLR and the location of an object on the quasar MS diagram.…”

“…In our previous works (Panda et al, 2017(Panda et al, , 2018(Panda et al, , 2019a we were successful in modelling almost the entire MS diagram constructed for over 20,000 SDSS quasars. In the past studies, we had incorporated only two of the aforementioned physical parameters of the super massive black hole i.e., black hole mass and accretion rate.…”