High Eddington quasars as discovery tools: current state and challenges

Abstract

A landmark of accretion processes in active galactic nuclei (AGN) is the continuum originating from a complex structure, i.e., an accretion disk and a corona around a supermassive black hole. Modelling the broad-band spectral energy distribution (SED) effectively ionizing the gas-rich broad emission line region (BLR) is key to understanding the various radiative processes at play and their importance that eventually leads to the emission from diverse physical conditions. Photoionization codes are a useful tool to investigate two aspects, the importance of the shape of the spectral energy distribution, and the physical conditions in the broad emission line region. In this work, we critically review long-standing issues pertaining to the spectral energy distribution shape and the anisotropic continuum radiation from the central regions around the accreting supermassive black holes (few 10–100 gravitational radii), with a focus on black holes accreting at high rates, possibly much above the Eddington limit. The anisotropic emission is a direct consequence of the development of a geometrically and optically thick structure at regions very close to the black hole due to a marked increase in the accretion rates. The analysis presented in this paper took advantage of the look at the diversity of the type-1 active galactic nuclei provided by the main sequence of quasars. The main sequence permitted us to assess the importance of the Eddington ratio and hence to locate the super Eddington sources in observational parameter space, as well as to constrain the distinctive physical conditions of their line-emitting BLR. This feat is posing the basis for the exploitation of quasars as cosmological distance indicators, hopefully allowing us to use the fascinating super Eddington quasars up to unprecedented distances.

UV FeII emission model of HE 0413−4031 and its relation to broad-line time delays

“…In multi-object statistical samples, there is an overall correlation between the quasar luminosity and the UV FeII strength (Clowes et al 2016). Several works (Marziani et al 2003;Shen & Ho 2014;Panda et al 2019c;Zheng 2021;Panda & Marziani 2023) claim that the FeII strength can actually be used as the Eddington ratio indicator.…”

Spectral Variability Studies in Active Galactic Nuclei: Exploring Continuum and Emission Line Regions in the Age of LSST and JWST

“…This growth has been primarily driven by the inclusion of sources monitored under the SEAMBH project [25,26,28,100,106,112], as well as contributions from the SDSS-RM campaigns [30,111,113] and OzDES survey (see, e.g., [109]). However, this expansion has introduced a new challenge: an inherent dispersion in the R BLR -L 5100 relation that has become apparent after incorporating these new sources (as depicted in Figure 1 of Panda and Marziani [114]). Interestingly, some of these new sources have contributed to an increase in the dispersion for the relation, which correlates with the Eddington ratio.…”

“…Interestingly, some of these new sources have contributed to an increase in the dispersion for the relation, which correlates with the Eddington ratio. Studies have found that the sources that demonstrate larger deviation from the empirical R BLR -L 5100 relation are found to have higher Eddington ratios [31,114,115].…”

First Detection of Outflowing Gas in the Outskirts of the Broad-line Region in 1H 0707−495*

“…This implies a higher accretion rate relative to the Eddington value compared with Seyfert 1 galaxies with broad optical lines (see Komossa 2018, for a comprehensive review). A special subset of this class, known as extreme NLS1s or xA sources within the mainsequence classification (Marziani et al 2018;Panda et al 2019;Marinello et al 2020), shows highly super-Eddington accretion sources (Jin et al 2017;Panda & Marziani 2023). These xA objects exhibit spectral features such as extremely prominent Fe II (i.e., R 4570 > 1.5; Wang et al 2014;Du et al 2015;Marinello et al 2020), very rapid X-rays, and UV flux variability (Gallo 2006).…”