Quasars are rapidly accreting supermassive black holes at the centres of massive galaxies. They display a broad range of properties across all wavelengths, reflecting the diversity in the physical conditions of the regions close to the central engine. These properties, however, are not random, but form well-defined trends. The dominant trend is known as 'Eigenvector 1', in which many properties correlate with the strength of optical iron and [O III] emission. The main physical driver of Eigenvector 1 has long been suspected to be the quasar luminosity normalized by the mass of the hole (the 'Eddington ratio'), which is an important parameter of the black hole accretion process. But a definitive proof has been missing. Here we report an analysis of archival data that reveals that the Eddington ratio indeed drives Eigenvector 1. We also find that orientation plays a significant role in determining the observed kinematics of the gas in the broad-line region, implying a flattened, disk-like geometry for the fast-moving clouds close to the black hole. Our results show that most of the diversity of quasar phenomenology can be unified using two simple quantities: Eddington ratio and orientation.

The diversity of quasars unified by accretion and orientation

The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of physical and dynamical modeling of quasar structure. We discuss the empirical correlates of the so-called “main sequence” associated with the quasar Eigenvector 1, its governing physical parameters and several implications on our view of the quasar structure, as well as some luminosity effects associated with the virialized component of the line emitting regions. We also briefly discuss quasars in a segment of the main sequence that includes the strongest FeII emitters. These sources show a small dispersion around a well-defined Eddington ratio value, a property which makes them potential Eddington standard candles.

/pdf/a-main-sequence-for-quasars-1wvos92roy.pdf

A Main Sequence for Quasars

Recently some pessimism has been expressed about our lack of progress in understanding quasars over more than fifty year since their discovery. It is worthwhile to look back at some of the progress that has been made – but still lies under the radar – perhaps because few people are working on optical/UV spectroscopy in this field. Great advances in understanding quasar phenomenology have emerged using eigenvector techniques. The 4D eigenvector 1 context provides a surrogate H-R Diagram for quasars with a source main sequence driven by Eddington ratio convolved with line-of-sight orientation. Appreciating the striking differences between quasars at opposite ends of the main sequence (so-called population A and B sources) opens the door towards a unified model of quasar physics, geometry and kinematics. We present a review of some of the progress that has been made over the past 15 years, and point out unsolved issues.

/pdf/quasars-in-the-4d-eigenvector-1-context-a-stroll-down-memory-g8ygduqxwv.pdf

Quasars in the 4D Eigenvector 1 Context: a stroll down memory lane

ABSTRACT We present the mid-infrared (MIR) light curves (LC) of 10 superluminous supernovae (SLSNe) at z &amp;lt; 0.12 based on WISE data at 3.4 and 4.6 $\mu$m. Three of them, including PS15br, SN 2017ens, and SN 2017err show rebrightening which started at 200–400 d and ended at 600–1000 d, indicating the presence of dust. In four of the left seven SLSNe, dust emission was detected with monochromatic luminosities of $10^7\sim 10^8\, {\rm L}_\odot$ at epochs of 100–500 d based on MIR colours W1 − W2 ∼ 1. Among the three SLSNe which show rebrightening, we further analysed PS15br and SN 2017ens. We modelled the SEDs at 500–700 d, which gives dust temperatures of 600–1100 K, dust masses of $\gtrsim 10^{-2}\, {\rm M}_\odot$, and luminosities of $10^8\sim 10^9\, {\rm L}_\odot$. Considering the time delay and the huge amount of energy released, the emitting dust can hardly be pre-existing dust heated whether collisionally by shocks or radiatively by peak SLSN luminosity or shock emission. Instead, it can be newly formed dust additionally heated by the interaction of circumstellar medium, indicated by features in their spectra and slowly declining bolometric LCs. The dust masses appear to be ten times greater than those formed in normal core-collapse supernovae at similar epochs. Combining with the analysis of SN 2018bsz by Chen et al. (2021), we suggest that SLSNe have higher dust formation efficiency, although future observations are required to reach a final conclusion. 

OUP accepted manuscript

Recently some pessimism has been expressed about our lack of progress in understanding quasars over the 50+ year since their discovery. It is worthwhile to look back at some of the progress that has been made - but still lies under the radar - perhaps because few people are working on optical/UV spectroscopy in this field. Great advances in understanding quasar phenomenology have emerged using eigenvector techniques. The 4D eigenvector 1 context provides a surrogate H-R Diagram for quasars with a source main sequence driven by Eddington ratio convolved with line-of-sight orientation. Appreciating the striking differences between quasars at opposite ends of the main sequence (so-called population A and B sources) opens the door towards a unified model of quasar physics, geometry and kinematics. We present a review of some of the progress that has been made over the past 15 years, and point out unsolved issues.

Quasars in the 4D Eigenvector 1 Context: A stroll down memory lane

X-ray properties of active galactic nuclei with optical fe ii emission

CSS J102913 + 404220 is an atypical narrow-line Seyfert 1 galaxy with an energetic optical outburst occurring co-spatially with its nucleus. We present a detailed analysis of multi-wavelength photometric and spectroscopic observations of this object covering a period of a decade since outburst. We detect mid-infrared (MIR) ﬂares delayed by about two months relative to the optical outburst and with an extremely high peak luminosity of L 4 . 6 µ m > 10 44 erg s − 1 . The MIR peak luminosity is at least an order of magnitude higher than any known supernovae explosions, suggesting the optical outburst might be due to a stellar tidal disruption event (TDE). We ﬁnd late-time X-ray brightening by a factor of (cid:38) 30 with respect to what is observed about 100 days after the optical outburst peak, followed by a ﬂux fading by a factor of ∼ 4 within two weeks, making it one of the active galactic nuclei (AGNs) with extreme variability. Despite the dramatic X-ray variability, there are no coincident strong ﬂux variations in optical, UV, and MIR bands. This unusual variability behavior has been seen in other highly accreting AGNs and could be attributed to absorption variability. In this scenario, the decrease in the covering factor of the absorber with accretion rate could cause the X-ray brightening, possibly induced by the TDE. Most strikingly, while the UV / optical continuum remains almost unchanged with time, an evident enhancement in the ﬂux of the H α broad emission line is observed about a decade after the nuclear optical outburst, which is an anomalous behavior never seen in any other AGN. Such an H α anomaly could be explained by the replenishment of gas clouds and excitation within the broad line region (BLR) that perhaps originates from its interaction with outﬂowing stellar debris. Our results highlight the importance of the late-time evolution of a TDE, which can a ﬀ ect the accreting properties of the AGN, as suggested by recent simulations.

Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy

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X-ray properties of active galactic nuclei with optical fe ii emission

Discovery of late-time X-ray flare and anomalous emission line enhancement after the nuclear optical outburst in a narrow-line Seyfert 1 Galaxy