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The last few years have seen the confirmation of several trends associated with the quasar main sequence. The idea of a main sequence for quasars is relatively recent, and its full potential for the observational classification and contextualization of quasars' properties has yet to be fully exploited. The main sequence drivers are discussed in terms of the properties of extreme objects. We briefly summarize developments that constrain the viewing angle of the accretion disk in a particular class of quasars (extreme Population B, radiating at low Eddington ratio), as well as inferences on the chemical composition of the broad line emitting gas, and on the nature of radio emission along the quasar main sequence. © 2021 Wiley-VCH GmbH., N. Bon and E. Bon acknowledge the support of Serbian Ministry of Education, Science and Technological Development, through the contract number 451-03-68/2020-14/200002., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Nuclear Activity in Galaxies Across Cosmic Time, Proceedings of the conference held 7-11 October 2019 in Addis Ababa, Ethiopia. Edited by Mirjana Pović et al. Proceedings of the International Astronomical Union, Volume 356, pp. 66-71, The main sequence offers a method for the systematization of quasar spectral properties. Extreme FeII emitters (or extreme Population A, xA) are believed to be sources accreting matter at very high rates. They are easily identifiable along the quasar main sequence, in large spectroscopic surveys over a broad redshift range. The very high accretion rate makes it possible that massive black holes hosted in xA quasars radiate at a stable, extreme luminosity-to-mass ratio. After reviewing the basic interpretation of the main sequence, we report on the possibility of identifying virial broadening estimators from low-ionization line widths, and provide evidence of the conceptual validity of redshift-independent luminosities based on virial broadening for a known luminosity-to-mass ratio., AdO acknowledges financial support from Spanish grants AYA2016-76682-C3-1-P and SEV-2017-0709.

Context. The quasar class of extreme Population A (xA) (also known as super-Eddington accreting massive black holes, SEAMBHs) has been hailed as potential distance indicators for cosmology. Aims. The aim of this paper is to define tight criteria for their proper identification, starting from the main selection criterion RFeII > 1, and to identify potential intruders that do not meet the selection criteria, which nonetheless have been selected as xA because of the coarseness of automatic searches. The inclusion of the spurious xA sources may dramatically increase the dispersion in the Hubble diagram of quasars, which were obtained from virial luminosity estimates. Methods. We studied a sample of 32 low-z quasars that were originally selected from the seventh data release of the Sloan Digital Sky Survey as xA or SEAMBHs, which have been proved to be almost certainly misclassified sources. All of them show moderate to strong Fe II emission and the large majority show strong absorption features in their spectra which are typical of fairly evolved stellar populations. We performed a simultaneous fit of a host galaxy spectrum, active galactic nucleus (AGN) continuum, FeII template, and emission lines to spectra, using the fitting technique based on ULySS, the full spectrum fitting package. We derived the main accretion parameters (i.e., luminosity, black hole mass, and Eddington ratio) and investigate the relation between host galaxy properties and AGN. Results. For sources in our sample with spectral types that correspond to a relatively low Eddington ratio, we find an overall consistency between HβNC, [O III]λλ4959,5007 line shifts, and the mean stellar velocity obtained from the host galaxy fit (within|60| km s-1). Only one source in our sample qualifies as a xA source. Conclusions. The correct classification of spectra that were contaminated by heavy absorption requires careful determination of the host galaxy spectrum. Contamination and misclassification are not usual in the identification of the xAs, nor at low z or at high z. We find a high fraction of host galaxy spectrum; in half of the sample this is even higher than 40%. When absorption lines are prominent, and the fraction of the host galaxy is high, host galaxy spectrum mimics FeII, which may result in a mistaken identification of FeII spectral features. We have identified several stellar absorption lines that, along with the continuum shape, may lead to an overestimate of RFeII, and therefore to the misclassification of sources as xA sources. © ESO 2020., This research is part of the projects 176001 "Astrophysical spectroscopy of extragalactic objects" and 176003 "Gravitation and the large scale structure of the Universe", funded by Ministry of Education, Science and Technological Development of the Republic of Serbia. PM and MDO acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. PM also acknowledges the Programa de Estancias de Investigacion (PREI) No. DGAP/DFA/2192/2018 of UNAM. A.d.O. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through grant AYA2016-76682-C3-1-P and from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). ML. M. A. acknowledges financial support of National Science Centre, Poland, grant No. 2017/26/A/ST9/00756 (Maestro 9). DD acknowledges support from grants PAPIIT, UNAM 113719, Mexico D.F. 04510, Mexico. AN acknowledges support from grant CONACyT research fellow -Instituto de Astronomia, UNAM, Mexico D.F. 04510, Mexico. We thank to Pu Du for his help and constructive comments. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org/.The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

Quasars accreting matter at very high rates (known as extreme Population A [xA] quasars, possibly associated with super-Eddington accreting massive black holes) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. At a more fundamental level, xA quasars are of special interest in studies of the physics of AGNs and host galaxy evolution. However, their observational properties are largely unknown. xA quasars can be identified in relatively large numbers from major optical surveys over a broad range of redshifts, and efficiently separated from other type-1 quasars thanks to selection criteria defined from the systematically-changing properties along the quasars main sequence. It has been possible to build a sample of ~250 quasars at low and intermediate redshift, and larger samples can be easily selected from the latest data releases of the Sloan Digital Sky Survey. A large sample can clarify the main properties of xA quasars which are expected—unlike the general population of quasars—to radiate at an extreme, well-defined Eddington ratio with small scatter. As a result of the small scatter in Eddington ratio shown by xA quasars, we propose a method to derive the main cosmological parameters based on redshift-independent “virial luminosity” estimates from measurements of emission line widths, roughly equivalent to the luminosity estimates based from line width in early and late type galaxies. A major issue related to the cosmological application of the xA quasar luminosity estimates from line widths is the identification of proper emission lines whose broadening is predominantly virial over a wide range of redshift and luminosity. We report on preliminary developments using the AlIIIλ1860 intermediate ionization line and the Hydrogen Balmer line Hβ as virial broadening estimators, and we briefly discuss the perspective of the method based on xA quasars. © Copyright © 2020 Dultzin, Marziani, de Diego, Negrete, Del Olmo, Martínez-Aldama, D'Onofrio, Bon, Bon and Stirpe., This research is part of the projects 176001-Astrophysical spectroscopy of extragalactic objects and 176003-Gravitation and the large scale structure of the Universe, funded by Ministry of Education, Science and Technological Development of the Republic of Serbia.

Quasars accreting matter at very high rates (known as extreme Population A [xA]) may provide a new class of distance indicators covering cosmic epochs from present day up to less than 1 Gyr from the Big Bang. We report on the developments of a method that is based on "virial luminosity" estimates from measurements of emission line widths of xA quasars. The approach is conceptually equivalent to the virial estimates based on early and late type galaxies. The main issues related to the cosmological application of luminosity estimates from xA quasar line widths are the identification of proper emission lines whose broadening is predominantly virial over a wide range of luminosity, and the assessment of the effect of the emitting region orientation with respect to the line of sight. We report on recent developments concerning the use of the AlIII 1860 intermediate ionisation line and of the Hydrogen Balmer line H$\beta$ as "virial broadening estimators.", Comment: Submitted as part of the special issue "Spectral Line Shapes in Astrophysics and Related Topics" to appear in the Contributions of the Astronomical Observatory of Skalnate' Pleso; 13 pages, 5 figures

Proceedings of the International Astronomical Union, Symposium S342 (Perseus in Sicily: From Black Hole to Cluster Outskirts) May 2018, We present a method that uses photoionization codes (CLOUDY) to estimate the supermassive black hole masses (MBH) for quasars at low and high redshift. This method is based on the determination of the physical conditions of the broad line region (BLR) using observational diagnostic diagrams from line ratios in the UV. We also considered that the density and metallicity of the BLR in quasars at high z could be different from those at the nearby Universe. The computed black hole masses obtained using this method are in agreement with those derived from the method of reverberation mapping. © International Astronomical Union 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., Highly accreting quasars show fairly distinctive properties in their optical, UV, and X spectra, and are easy to recognize because of their specific location in the quasar main sequence: they are the strongest optical FeII emitters. They show a surprisingly high rate of radio detections and, at variance with the classical radio-loud (jetted) sources, the origin of their radio emission is probably "thermal." The chemical composition of the broad line emitting gas implies high metallicity values, above 10 times solar. A fraction of highly accreting quasars at intermediate and high redshift might therefore be in a particular evolutionary stage that is unobscured albeit still involving a contribution of nuclear and circum-nuclear star formation in their multifrequency properties. © 2021. The Author(s). Published by the American Astronomical Society., A.d.O. acknowledges financial support from the Spanish MCIU grant PID2019-106027GB-C41 and from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award for the Instituto de Astrofsica de An- daluca (SEV-2017-0709).

Tables A.1–A.3 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/630/A110, Context. When can an active galactic nucleus (AGN) be considered radio loud (RL)? Following the established view of the AGNs inner workings, an AGN is RL if associated with relativistic ejections emitting a radio synchrotron spectrum (i.e., it is a “jetted” AGN). In this paper we exploit the AGN main sequence that offers a powerful tool to contextualize radio properties. Aims. If large samples of optically-selected quasars are considered, AGNs are identified as RL if their Kellermann’s radio loudness ratio RK > 10. Our aims are to characterize the optical properties of different classes based on radio loudness within the main sequence and to test whether the condition RK > 10 is sufficient for the identification of RL AGNs, since the origin of relatively strong radio emission may not be necessarily due to relativistic ejection. Methods. A sample of 355 quasars was selected by cross-correlating the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters survey (FIRST) with the twelfth release of the Sloan Digital Sky Survey Quasar Catalog published in 2017. We classified the optical spectra according to their spectral types along the main sequence of quasars. For each spectral type, we distinguished compact and extended morphology (providing a FIRST-based atlas of radio maps in the latter case), and three classes of radio loudness: detected ( specific flux ratio in the g band and at 1.4 GHz, R′K < 10), intermediate (10 ≤ R′K < 70), and RL (R′K ≥ 70). Results. The analysis revealed systematic differences between radio-detected (i.e., radio-quiet), radio-intermediate, and RL classes in each spectral type along the main sequence. We show that spectral bins that contain the extreme Population A sources have radio power compatible with emission by mechanisms ultimately due to star formation processes. RL sources of Population B are characteristically jetted. Their broad Hβ profiles can be interpreted as due to a binary broad-line region. We suggest that RL Population B sources should be preferential targets for the search of black hole binaries, and present a sample of binary black hole AGN candidates. Conclusions. The validity of the Kellermann’s criterion may be dependent on the source location along the quasar main sequence. The consideration of the main sequence trends allowed us to distinguish between sources whose radio emission mechanisms is jetted from the ones where the mechanism is likely to be fundamentally different.© ESO 2019, PM and MDO acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. PM also acknowledges the Programa de Estancias de Investigación (PREI) No. DGAP/DFA/2192/2018 of UNAM. AdO acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through grant AYA2016-76682-C3-1-P and from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). The relevant research is part of the project 176001 “Astrophysical spectroscopy of extragalactic objects” supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia

Open Access.-Attribution 4.0 International (CC BY 4.0), 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.© Copyright © 2018 Marziani, Dultzin, Sulentic, Del Olmo, Negrete, Martínez-Aldama, D'Onofrio, Bon, Bon and Stirpe., AD and MM-A acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through grants AYA2013-42227-P and AYA2016-76682-C3-1-P. DD and CN acknowledge support from grants PAPIIT108716, UNAM, and CONACyT221398. EB and NB acknowledge grants 176003 Gravitation and the large scale structure of the Universe and 176001 Astrophysical spectroscopy of extragalactic objects supported by the Ministry of Education and Science of the Republic of Serbia.

Context. The most highly accreting quasars are of special interest in studies of the physics of active galactic nuclei (AGNs) and host galaxy evolution. Quasars accreting at high rates (L=LEdd_ 1) hold promise for use as >standard candles>: Distance indicators detectable at very high redshift. However, their observational properties are still largely unknown. Aims. We seek to identify a significant number of extreme accretors. A large sample can clarify the main properties of quasars radiating near L=LEdd_ 1 (in this paper they are designated as extreme Population A quasars or simply as extreme accretors) in the Hβ spectral range for redshift .0:8. Methods. We use selection criteria derived from four-dimensional Eigenvector 1 (4DE1) studies to identify and analyze spectra for a sample of 334 candidate sources identified from the SDSS DR7 database. The source spectra were chosen to show a ratio RFeII between the FeII emission blend at Λ4570 and Hβ, RFeII > 1. Composite spectra were analyzed for systematic trends as a function of Feii strength, line width, and [Oiii] strength. We introduced tighter constraints on the signal-to-noise ratio (S/N) and RFeII values that allowed us to isolate sources most likely to be extreme accretors. Results. We provide a database of detailed measurements. Analysis of the data allows us to confirm that Hβ shows a Lorentzian function with a full width at half maximum (FWHM) of Hβ ≤ 4000 km s. We find no evidence for a discontinuity at 2000 km s in the 4DE1, which could mean that the sources below this FWHM value do not belong to a different AGN class. Systematic [Oiii] blue shifts, as well as a blueshifted component in Hβ are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of Hβ is still affected by the blueshifted emission; however, the effect is non-negligible if the FWHM Hβ is used as a >virial broadening estimator> (VBE).We emphasize a strong effect of the viewing angle on Hβ broadening, deriving a correction for those sources that shows major disagreement between virial and concordance cosmology luminosity values. Conclusions. The relatively large scatter between concordance cosmology and virial luminosity estimates can be reduced (by an order of magnitude) if a correction for orientation effects is included in the FWHM Hβ value; outflow and sample definition yield relatively minor effects.© ESO 2018., D. Dultzin and A. Negrete acknowledge support form grant IN108716 PAPIIT UNAM and CONACyT project CB-221398. P.M. and M.D.O. acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. M. L. Martínez-Aldama acknowledges a CONACyT postdoctoral fellowship. A. del Olmo, M. L. Martínez-Aldama and J. W. Sulen-tic acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through grants AYA2013-42227-P and AYA2016-76682-C3-1-P. J. This research is part of projects 176003 “Gravitation and the large scale structure of the Universe” and 176001 “Astrophysical spectroscopy of extragalactic objects” supported by the Ministry of Education and Science of the Republic of Serbia.

Context. Quasars radiating at extreme Eddington ratios (hereafter xA quasars) are likely a prime mover of galactic evolution and have been hailed as potential distance indicators. Their properties are still scarcely known. Aims. We aim to test the effectiveness of the selection criteria defined on the >4D Eigenvector 1> (4DE1) for identifying xA sources. We provide a quantitative description of their rest-frame UV spectra (1300-2200 Å) in the redshift range 2 ≤ z ≤ 2.9, with a focus on major emission features. Methods. Nineteen extreme quasar candidates were identified using 4DE1 selection criteria applied to SDSS spectra: Alλ1860Siλ1892 ≥ 0.5 and Cλ1909/Siλ1892 ≤ 1. The emission line spectra was studied using multicomponent fits of deep spectroscopic observations (S/N ≥ 40-50; spectral resolution ≈ 250 km s) obtained with the OSIRIS at Gran Telescopio Canarias (GTC). Results. GTC spectra confirm that almost all of these quasars are xA sources with very similar properties. We provide spectrophotometric and line profile measurements for the Siλ1397+O, Cλ1549+Heλ1640, and the 1900 Å blend. This last feature is found to be predominantly composed of Alλ1860, Siλ1892 and Fe emission features, with weak Cλ1909. The spectra can be characterized as very low ionization (ionization parameter, logU ∼ -3), a condition that explains the significant Fe emission observed in the spectra. xA quasars show extreme properties in terms of Cλ1549 equivalent width and blueshift amplitudes. Cλ1549 shows low equivalent width, with a median value of 15 Å (≤ 30 Å for the most sources), and high or extreme blueshift amplitudes (-5000 ≤ c(1/2) ≤ -1000 km s). Weak-lined quasars appear as extreme xA quasars and not as an independent class. The Cλ1549 high amplitude blueshifts coexists in all cases save one with symmetric and narrower Alλ1860 and Siλ1892 profiles. Estimates of the Eddington ratio using the Alλ1860 FWHM as a virial broadening estimator are consistent with the ones of a previous xA sample. Conclusions. xA quasars show distinguishing properties that make them easily identifiable in large surveys and potential >standard candles> for cosmological applications. It is now feasible to assemble large samples of xA quasars from the latest data releases of the SDSS. We provide evidence that Alλ1860 could be associated with a low-ionization virialized subsystem, supporting previous suggestions that Al is a reliable virial broadening estimator.© ESO 2018., AdO, MLMA and JWS acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through grants AYA2013-42227-P and AYA2016-76682-C3-1-P. MLMA, PM and MDO acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. JP acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through grants AYA2013-40609-P and AYA2016-76682-C3-3-P.

Open Access.--Attribution 4.0 International (CC BY 4.0), We present preliminary results of a spectroscopic analysis for a sample of type 1 highly accreting quasars (L/L-Edd similar to 1.0) at high redshift, z similar to 2-3. The quasars were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope located at the Observatorio del Roque de los Muchachos in La Palma. The highly accreting quasars were identified using the 4D Eigenvector 1 formalism, which is able to organize type 1 quasars over a broad range of redshift and luminosity. The kinematic and physical properties of the broad line region have been derived by fitting the profiles of strong UV emission lines such as AlIII lambda 1860, SiIII]lambda 1892 and CIII]lambda 1909. The majority of our sources show strong blueshifts in the high-ionization lines and high Eddington ratios which are related with the productions of outflows. The importance of highly accreting quasars goes beyond a detailed understanding of their physics: their extreme Eddington ratio makes them candidates standard candles for cosmological studies.© Copyright © 2018 Martínez-Aldama, Del Olmo, Marziani, Sulentic, Negrete, Dultzin, Perea and D'Onofrio., MM-A acknowledge the postdoctoral grant from the CONACyT. MM-A and AD acknowledge financial support from Spanish Ministry for Economy and Competitiveness through grants AYA2013-42227-P and AYA2016-76682-C3-3-1-P.

We present a multiwavelength spectral study of the quasar HE0359-3959, which has been identified as an extreme radiating source at intermediate redshift (z=1.5209). Along the spectral range, the different ionic species give information about the substructures in the broad line region. The presence of a powerful outflow with an extreme blueshifted velocity of $\sim$-6000$\pm$500 km s$^{-1}$ is shown in the CIV{\lambda}1549 emission line. A prominent blueshifted component is also associated with the 1900{\AA} blend, resembling the one observed in CIV{\lambda}1549. We detect a strong contribution of very the low-ionization lines, FeII and Near-Infrared CaII triplet. We find that the physical conditions for the low, intermediate and high-ionization emission lines are different, which indicate that the emission lines are emitted in different zones of the broad line region. The asymmetries shown by the profiles reveal different forces over emitter zones. The high-ionization region is strongly dominated by radiation forces, which also affect the low and intermediate-ionization emitter region, commonly governed by virial motions. These results support the idea that highly radiating sources host a slim disk., Comment: 10 pages, 3 figures

We propose the use of quasars with accretion rate near the Eddington ratio (extreme quasars) as standard candles. The selection criteria are based on the Eigenvector 1 (E1) formalism. Our first sample is a selection of 334 optical quasar spectra from the SDSS DR7 database with a S/N > 20. Using the E1, we define primary and secondary selection criteria in the optical spectral range. We show that it is possible to derive a redshift-independent estimate of luminosity for extreme Eddington ratio sources. Our results are consistent with concordance cosmology but we need to work with other spectral ranges to take into account the quasar orientation, among other constrains.

Ton 34 recently transitioned from non-absorbing quasar into a BALQSO.Here, we report new HST-STIS observations of this quasar. Along with CIV absorption, we also detect absorption by NV+Ly alpha and possibly OVI+Ly beta. We follow the evolution of the CIV BAL, and find that, for the slower outflowing material, the absorption trough varies little (if at all) on a rest-frame timescale of 2 yr. However, we detect a strong deepening of the absorption in the gas moving at larger velocities (-20,000 - -23,000 km s-1). The data is consistent with a multistreaming flow crossing our line of sight to the source. The transverse velocity of the flow should be few thousand km s-1, similar to the rotation velocity of the BLR gas (2,600 km s-1). By simply assuming Keplerian motion, these two components must have similar locations, pointing to a common outflow forming the BLR and the BAL. We speculate that BALs, mini-BALs, and NALs, are part of a common, ubiquitous, accretion-disk outflow in AGN, but become observable depending on the viewing angle towards the flow. The absorption troughs suggest a wind covering only 20% of the emitting source, implying a maximum size of 10^-3 pc for the clouds forming the BAL/BLR medium. This is consistent with constraints of the BLR clouds from X-ray occultations. Finally, we suggest that the low excitation broad emission lines detected in the spectra of this source lie beyond the wind, and this gas is probably excited by the shock of the BAL wind with the surrounding medium., Accepted for publication in MNRAS

Highly accreting quasars are characterized by distinguishing properties in the 4D eigenvector 1 parameter space that make them easily recognizable over a broad range range of redshift and luminosity. The 4D eigenvector 1 approach allows us to define selection criteria that go beyond the restriction to Narrow Line Seyfert is identified at low redshift. These criteria are probably able to isolate sources with a defined physical structure i.e., a geometrically thick, optically thick advection-dominated accretion disk (a “slim” disk). We stress that the importance of highly accreting quasars goes beyond the understanding of the details of their physics: their Eddington ratio is expected to saturate toward values of order unity, making them possible cosmological probes.

We describe an alternate way to estimate Broad Line Region (BLR) radii for type-1 AGN based on determination of physical conditions in the BLR under the assumption that the line emitting gas is photoionized by a central continuum source. We derive “diagnostic” intensity ratios involving UV lines Al iii λ 1860, Si iii ] λ 1892 and C iv λ 1549 which enable us to compute the ionizing photon flux, and hence BLR radius from the ionization parameter definition. We compare our estimates of BLR radii with values independently obtained from reverberation monitoring of H β and, in a few cases, of C iv λ 1549. We analyze the interpretation of the photoionization estimates in the 4D eigenvector 1 context, and discuss in some detail the case of 3C 390.3. For this object we are able to provide not only the ionizing photon flux, but also an estimate of density and ionization parameter from the measured diagnostic ratios. We also compare black hole masses obtained from this method with values derived from widely-applied correlations between mass, line broadening and luminosity. Good agreement is found for both radius and black hole mass comparisons.

The inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the quasar broad line region (BLR) structure and dynamics, including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars. We carried out an analysis of the CIV 1549 and Hbeta line profiles of 28 Hamburg-ESO high luminosity quasars and of 48 low-z, low luminosity sources in order to test whether the high-ionization line CIV 1549 width could be correlated with Hbeta and be used as a virial broadening estimator. We analyze intermediate- to high-S/N, moderate resolution optical and NIR spectra covering the redshifted CIV and H$\beta$ over a broad range of luminosity log L ~ 44 - 48.5 [erg/s] and redshift (0 - 3), following an approach based on the quasar main sequence. The present analysis indicates that the line width of CIV 1549 is not immediately offering a virial broadening estimator equivalent to H$\beta$. At the same time a virialized part of the BLR appears to be preserved even at the highest luminosities. We suggest a correction to FWHM(CIV) for Eddington ratio (using the CIV blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity. Great care should be used in estimating high-L black hole masses from CIV 1549 line width. However, once corrected FWHM(CIV) values are used, a CIV-based scaling law can yield unbiased MBH values with respect to the ones based on H$\beta$ with sample standard deviation ~ 0.3 dex., Comment: 43 pages, 15 Figures, submitted to A&A

Quasars accreting matter at very high rates (known as extreme Population A (xA) or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less than 1 Gyr from the Big Bang. The very high accretion rate makes it possible that massive black holes hosted in xA quasars can radiate at a stable, extreme luminosity-to-mass ratio. This in turn translates into stable physical and dynamical conditions of the mildly ionized gas in the quasar low-ionization line emitting region. In this contribution, we analyze the main optical and UV spectral properties of extreme Population A quasars that make them easily identifiable in large spectroscopic surveys at low- (z . 1) and intermediate-z (2 . z . 2.6), and the physical conditions that are derived for the formation of their emission lines. Ultimately, the analysis supports the possibility of identifying a virial broadening estimator from low-ionization line widths, and the conceptual validity of the redshift-independent luminosity estimates based on virial broadening for a known luminosity-to-mass ratio, P.M. wishes to thank the Scientific Organizing Committee of the Symposium on the Physics of Ionized Gases (SPIG 2018) meeting for inviting the topical lecture on which this paper is based, and acknowledges the Programa de Estancias de Investigación (PREI) No. DGAP/DFA/2192/2018 of Universidad Nacional Autónoma de México (UNAM), where this paper was written. The relevant research is part of the project 176001 “Astrophysical spectroscopy of extragalactic objects” and 176003 “Gravitation and the large scale structure of the Universe” supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia. M.L.M.-A. acknowledges a CONACyT postdoctoral fellowship. A.d.O. and M.L.M.-A. acknowledge financial support from the Spanish Ministry for Economy and Competitiveness through Grant Nos. AYA2013-42227-P and AYA2016-76682-C3-1-P. M.L.M.-A, P.M. and M.D. acknowledge funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. D.D. and A.N. acknowledge support from CONACyT through Grant No. CB221398. D.D. and C.A.N. are also thankful for the support from Grant No. IN108716 53 PAPIIT, UNAM, We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Broad emission lines in quasars enable us to "resolve" structure and kinematics of the broad line emitting region (BLR) thought to in- volve an accretion disk feeding a supermassive black hole. Interpretation of broad line measures within the 4DE1 formalism simplifies the apparent confusion among such data by contrasting and unifying properties of so-called high and low accreting Population A and B sources. H{\beta} serves as an estimator of black hole mass, Eddington ratio and source rest frame, the latter a valuable input for Civ{\lambda}1549 studies which allow us to isolate the blueshifted wind component. Optical and HST-UV spectra yield H{\beta} and Civ{\lambda}1549 spectra for low-luminosity sources while VLT-ISAAC and FORS and TNG-LRS provide spectra for high Luminosity sources. New high S/N data for Civ in high-luminosity quasars are presented here for comparison with the other previously published data. Comparison of H{\beta} and Civ{\lambda}1549 profile widths/shifts indicates that much of the emission from the two lines arise in regions with different structure and kinematics. Covering a wide range of luminosity and redshift shows evidence for a correlation between Civ{\lambda}1549 blueshift and source Eddington ratio, with a weaker trend with source luminosity (similar amplitude outflows are seen over 4 of the 5 dex luminosity range in our combined samples). At low luminosity (z < 0.7) only Population A sources show evidence for a significant outflow while at high luminosity the outflow signature begins to appear in Population B quasars as well., Comment: 18 pages, 11 figures

The most luminous quasars (with bolometric luminosities are ≳ 1047 erg/s) show a high prevalence of CIV λ1549 and [OIII]λλ4959,5007 emission line profiles with strong blueshifts. Blueshifts are interpreted as due to Doppler effect and selective obscuration, and indicate outflows occurring over a wide range of spatial scales. We found evidence in favor of the nuclear origin of the outflows diagnosed by [OIII]λλ4959,5007. The ionized gas mass, kinetic power, and mechanical thrust are extremely high, and suggest widespread feedback effects on the host galaxies of very luminous quasars, at cosmic epochs between 2 and 6 Gyr from the Big Bang. In this mini-review we summarize results obtained by our group and reported in several major papers in the last few years with an eye on challenging aspects of quantifying feedback effects in large samples of quasars.

Highly accreting quasars are possible cosmological probes, as their Eddington ratio is expected to saturate toward values of order unity. We present preliminary estimates of redshift- independent source luminosities and the Hubble diagram for quasars in the redshift range 0.1 ≲ z ≲ 2.6.

[Abridged] We compare broad emission line profiles and estimate line ratios for all major emission lines between Ly-alpha and H-beta in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high quality optical and UV spectra as well as the possibility to sample the spectroscopic diversity in the 4D Eigenvector 1 context . In the latter sense each source occupies a region (bin) in the FWHM(H-beta) vs. optical FeII strength plane that is significantly different from the others. High S/N H-beta emission line profiles are used as templates for modeling the other lines (Ly-alpha, CIV 1549, HeII 1640, Al III 1860, Si III] 1892, and Mg II 2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids (indicated as blue, broad and very broad component respectively). The broad component (high electron density, low ionization parameter; high column density) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad line emitting region (the reverberating component). The blue component emission (lower electron density; high ionization; low column density) arises in less optically thick gas; it is often thought to arise in an accretion disk wind. The least understood component involves the very broad component (high ionization and large column density). It is perhaps the most distinguishing characteristic of quasars with FWHM H-beta > 4000 km/s that belong to the so-called Population B of our 4DE1 space. Population A quasars (FWHM H-beta < 4000 km/s) are dominated by broad component emission in H-beta and blue component emission in CIV 1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type-1 quasars.

Accurate measurements of emission line properties are crucial to understand the physics of the broad line region in quasars. This region consists of warm gas that is closest to the quasar central engine and has not been spatially resolved for almost all sources. We present here an analysis of optical and IR data for a large sample of quasars, covering the Hi Hβ spectral region in the redshift range 0 ≲ z ≲ 2.5. Spectra were interpreted within the framework of the the so-called “eigenvector 1” parameter space, which can be viewed as a tentative H-R diagram for quasars. We stress the lack of spectral evolution in the low ionization lines of quasars, with prominent Fe ii emission also at z ≳ 2. We also show how selection effects influence the ability to find quasars radiating at low Eddington ratio in flux-limited surveys. The quasar similarity at different redshift is probably due to the absence of super-Eddington radiators (at least within the caveats of black hole mass and Eddington ratio determination discussed in this paper) as well as to the limited Eddington ratio range within which quasars seem to radiate.

The UV spectral range (1100 - 3000 A) contains the strongest resonance lines observed in active galactic nuclei (AGN). Analysis of UV line intensity ratios and profile shapes in quasar spectra provide diagnostics of physical and dynamical conditions in the broad line emitting region. This paper discusses properties of UV lines in type-1 AGN spectra, and how they lead an estimate of ionizing photon flux, chemical abundances, radius of the broad line emitting region and central black hole mass. These estimates are meaningfully contextualised through the 4D "eigenvector-1" (4DE1) formalism., Contributed paper presented at the ESO/NUVA/IAG Workshop on Challenges in UV Astronomy ESO, Garching, 7-11 October 2013. Accepted for publication in Astrophysics and Space Science

Determining the masses of the central compact object believed to power all active galactic nuclei is relevant to our understanding of their evolution and of their inner workings. Keys to present-day mass estimates are: (1) the assumption of line broadening due to virial motion of the emitting gas, (2) an estimate of the distance of broad-line emitting gas from the central compact object, and (3) a measure of the AGN luminosity. We discuss the merits and the limitations of an alternative method based on estimates of physical conditions in the broad line emitting region derived from an appropriate multi-component analysis of emission line profiles. This ‘photo-ionization method’, applied to UV intermediate-ionization lines appears to be promising for at least a sizable population of high-z quasars.

[Abridged] We have been exploring a spectroscopic unification for all known types of broad line emitting AGN. The 4D Eigenvector 1 (4DE1) parameter space shows promise as a unification capable of organizing quasar diversity on a sequence primarily governed by Eddington ratio. This paper considers the role of CIV 1549 measures with special emphasis on the CIV 1549 line shift as a principal 4DE1 diagnostic. We use HST archival spectra for 130 sources with S/N high enough to permit reliable CIV 1549 broad component (BC) measures. We find a CIV 1549 BC profile blueshift that is strongly concentrated among (largely radio-quiet: RQ) sources with FWHM(H beta BC) < 4000 km/s (which we call Population A). Narrow line Seyfert 1 (NLSy1, with FWHM H beta < 2000 km/s) sources belong to this population but do not emerge as a distinct class. The systematic blueshift, widely interpreted as arising in a disk wind/outflow, is not observed in broader lined AGN which we call Population B. We find new correlations between FWHM(CIV 1549 BC) and CIV 1549 line shift as well as the equivalent width of CIV 1549. They are seen only in Pop. A sources. CIV 1549 measures enhance the apparent dichotomy at FWHM(Hbeta BC) approx. 4000 \kms\ (Sulentic et al. 2000) suggesting that it has more significance in the context of Broad Line Region structure than the more commonly discussed RL vs. RQ dichotomy. Black hole masses computed from FWHM CIV 1549 BC for about 80 AGN indicate that the CIV 1549 width is a poor virial estimator. Comparison of mass estimates derived from Hbeta BC and CIV 1549 reveals that the latter show different and nonlinear offsets for population A and B sources. A significant number of sources also show narrow line CIV 1549 emission. We present a recipe for CIV 1549 narrow component extraction., Accepted for publication in the Astrophysical Journal

[Abridged] Context: The advent of 8-10m class telescopes makes possible for the first time detailed comparison of quasars with similar luminosity and very different redshifts. Aims: A search for z-dependent gradients in line emission diagnostics and derived physical properties by comparing, in a narrow bolometric luminosity range (log L ~ 46.1 +/- 0.4 [\ergss]), some of the most luminous local (z < 0.6) quasars with some of the lowest luminosity sources yet found at redshift z = 2.1 ~ 2.5. Method: Spectra for 22 high z sources were obtained with the 10.4m Gran Telescopio Canarias (GTC) while the HST (largely FOS) archive provides a low redshift control sample. Comparison is made in the context of the 4D Eigenvector 1 formalism meaning that we divide both source samples into high accreting Population A and low accreting Population B sources. Results: CIV 1549 shows very similar properties at both redshifts confirming at high redshift the CIV profile differences between Pop. A and B that are well established in local quasars. The CIV blueshift that appears quasi- ubiquitous in higher L sources is found in only half (Pop. A) of quasars observed in both of our samples. A CIV evolutionary Baldwin effect is certainly disfavored. We find evidence for lower metallicity in the GTC sample that may point toward a gradient with z. No evidence for a gradient in black hole mass or Eddington ratio is found. Conclusions: Spectroscopic differences established at low redshift are also present in much higher redshift quasars. Given that our samples involve sources with very similar luminosity the evidence for a systematic metallicity decrease, if real, points toward an evolutionary effect. Our samples appear representative of a slow evolving quasar population likely present at all redshifts., To appear in Astronomy & Astrophysics

We describe a method for estimating physical conditions in the broad-line region (BLR) for a significant subsample of Seyfert 1 nuclei and quasars. Several diagnostic ratios based on intermediate (Al III {lambda}1860, Si III] {lambda}1892) and high (C IV {lambda}1549, Si IV {lambda}1397) ionization lines in the UV spectra of quasars are used to constrain density, ionization, and metallicity of the emitting gas. We apply the method to two extreme Population A quasars-the prototypical NLSy1 I Zw 1 and higher z source SDSS J120144.36+011611.6. Under assumptions of spherical symmetry and pure photoionization we infer BLR physical conditions: low ionization (ionization parameter

Narrow-line Seyfert 1s (NLSy1s) are an ill-defined class. Work done over the past 20 years as well as recent analyses show a continuity in properties (e.g., Balmer line profiles, blueshifts of high-ionization lines) between sources with FWHM above and below 2000 km/s, the defining boundary of NLSy1s. This finding alone suggests that comparisons between samples of NLSy1s and rest of broad-line AGNs are most likely biased. NLSy1s can be properly contextualized by their location on the quasar main sequence originally defined by Sulentic et al 2000. At one end, NLSy1s encompass sources with strong FeII emission and associated with high Eddington ratio that hold the promise of becoming useful distance indicators; at the other end, at least some of them are sources with broad profiles seen face-on. Any rigid FWHM limit gives rise to some physical ambiguity, as the FWHM of low-ionization lines depends in a complex way on mass, Eddington ratio, orientation, and luminosity. In addition, if the scaling derived from luminosity and virial dynamics applies to the broad line regions, NLSy1s at luminosity higher than 1E47 erg/s become physically impossible. Therefore, in a broader context, a proper subdivision of two distinct classes of AGNs and quasars may be achieved by the distinction between Pop. A and B with boundary at = 4000 km/s in samples at z < 1, or on the basis of spectrophotometric properties which may ultimately be related to differences in accretion modes if high-luminosity quasars are considered., Contribution presented at the meeting Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe, held at the Padova Botanical Garden, Italy, on 9-13 April 2018

Quasars show a considerable spectroscopic diversity. However, the variety of quasar spectra at low redshifts is non-random: a principal component analysis applied to large samples customarily identifies two main eigenvectors. In this contribution we show that the range of quasar optical spectral properties observed at low-z and associated with the first eigenvector is preserved up to z ≈ 2 in a sample of high luminosity quasars. We also describe two major luminosity effects.