The physical driver of the optical Eigenvector 1 in Quasar Main Sequence

Quasars are complex sources, characterized by broad band spectra from radio through optical to X-ray band, with numerous emission and absorption features. However, Boroson & Green (1992) used Principal Component Analysis (PCA), and with this analysis they were able to show significant correlations between the measured parameters. The leading component, related to Eigenvector 1 (EV1) was dominated by the anticorrelation between the Fe${\mathrm{II}}$ optical emission and [OIII] line and EV1 alone contained 30% of the total variance. It opened a way in defining a quasar main sequence, in close analogy to the stellar main sequence on the Hertzsprung-Russel (HR) diagram (Sulentic et al. 2001). The question still remains which of the basic theoretically motivated parameters of an active nucleus (Eddington ratio, black hole mass, accretion rate, spin, and viewing angle) is the main driver behind the EV1. Here we limit ourselves to the optical waveband, and concentrate on theoretical modelling the Fe${\mathrm{II}}$ to H$\mathrm{\beta}$ ratio, and we test the hypothesis that the physical driver of EV1 is the maximum of the accretion disk temperature, reflected in the shape of the spectral energy distribution (SED). We performed computations of the H$\mathrm{\beta}$ and optical Fe${\mathrm{II}}$ for a broad range of SED peak position using CLOUDY photoionisation code. We assumed that both H$\mathrm{\beta}$ and Fe${\mathrm{II}}$ emission come from the Broad Line Region represented as a constant density cloud in a plane-parallel geometry. We expected that a hotter disk continuum will lead to more efficient production of Fe${\mathrm{II}}$ but our computations show that the Fe${\mathrm{II}}$ to H$\mathrm{\beta}$ ratio actually drops with the rise of the disk temperature. Thus either hypothesis is incorrect, or approximations used in our paper for the description of the line emissivity is inadequate.Comment: 12 pages, 4 figures, Accepted for publication in the Journal Frontiers in Astronomy and Space Science

The Quasar Main Sequence explained by the combination of Eddington ratio, metallicity and orientation

We address the effect of orientation of the accretion disk plane and the geometry of the broad-line region (BLR) as part of an effort to understand the distribution of quasars in the optical plane of the quasar main sequence. We utilize the photoionization code CLOUDY to model the BLR incorporating the grossly underestimated form factor ($f$). Treating the aspect of viewing angle appropriately, we confirm the dependence of the $R_{\mathrm{FeII}}$ sequence on Eddington ratio and on the related observational trends - as a function of the SED shape, cloud density and composition, verified from prior observations. Sources with $R_{\mathrm{FeII}}$ in the range 1 -- 2 (about 10\% of all quasars, the so-called extreme Population A [xA] quasars) are explained as sources of high, and possibly extreme Eddington ratio along the $R_{\mathrm{FeII}}$ sequence. This result has important implication for the exploitation of xA sources as distance indicators for Cosmology. $\mathrm{FeII}$ emitters with $R_{\mathrm{FeII}} > 2$ are very rare (<1\% of all type 1 quasars). Our approach also explains the rarity of these highest $\mathrm{FeII}$ emitters as extreme xA sources and constrains the viewing angle ranges with increasing H$\beta$ FWHM.Comment: 9 pages, 4 figures, 1 table; accepted for publication in Ap

High Eddington accreting quasar spectra as discovery tools: current state and challenges

Broad emitting line regions (BLR) in active galaxies are primarily emitted by photoionization processes that are driven by the incident continuum arising from the underlying, complex geometrical structure, i.e. accretion disk and corona around a supermassive black hole. Modelling the broad-band spectral energy distribution (SED) effective in ionizing the gas-rich BLR is key to understanding the various radiative processes at play and their importance that eventually leads to the emission of emission lines from diverse physical conditions. Photoionization codes are a useful tool to investigate two aspects - the importance of the shape of the SED, and the physical conditions in the BLR. In this work, we provide the first results focusing on a long-standing issue pertaining to the anisotropic continuum radiation from the very centres (few 10-100 gravitational radii) of these active galaxies. 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. Incorporating the radiation emerging from such a structure in our photoionization modelling, we are successful in replicating the observed emission line intensities, in addition to the remarkable agreement on the location of the BLR with current reverberation mapping estimates. This study took advantage of the look at the diversity of the Type-1 active galactic nuclei (AGNs) provided by the main sequence of quasars. The main sequence permitted to locate of the super Eddington sources in observational parameter space and to constrain the distinctive} physical conditions of their line-emitting BLR. This feat will eventually allow us to use the fascinating super Eddington quasars as probes to understand better the cosmological state of our Universe.Comment: 29 pages, 5 figures, 2 tables, based on the invited talk presented at the SPIG - 31st Summer School and International Symposium on the Physics of Ionized Gases, held between 05th - 09th September 202