arXiv subjects

P. Marziani

Publications and source records attributed to P. Marziani.

At least 37 records · Page 2Linked to original sources

arXiv2022

The intermediate-ionization lines as virial broadening estimators for Population A quasars

The identification of a virial broadening estimator in the quasar UV rest frame suitable for black hole mass computation at high redshift has become an important issue. We compare the HI Balmer H-beta line width to the ones of two intermediate ionization lines: the Aliii 1860 doublet and the Ciii] 1909 line, over a wide interval of redshift and luminosity (0 < z < 3.5; 43 < logL < 48.5 [erg a/]), for 48 sources belonging to the quasar population characterized by mid-to-high values of the Eddington ratio (Population A). The present analysis indicates that the line width of Aliii 1860 and H-beta are highly correlated, and can be considered equivalent for most Population A quasars over five orders of magnitude in luminosity; forCiii] 1909, multiplication by a constant correction factor xi ~ 1.25 is sufficient to bring the FWHM of Ciii] in agreement with the one of H-betaa. The statistical concordance between low-ionization and intermediate-ionization lines suggests that they predominantly arise from the same virialized part of the broad line region. However, blueshifts of modest amplitude (few hundred km /s) with respect to the quasar rest frame and an excess (~ 1.1) Aliii broadening with respect to H-beta are found in a fraction of our sample. Scaling laws to estimate M_BH of high redshift quasar using the Aliii and the Ciii] line widths have rms scatter ~ 0.3 dex. The Aliii scaling law takes the form log M_BH ~ 0.58 log L1700,44 + 2 log FWHM + 0.49 [solar masses].

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arXiv2021

The Main Sequence of quasars: the taming of the extremes

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 quasar 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.

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arXiv2021

X-ray spectroscopic survey of highly-accreting AGN

Improving our understanding of the nuclear properties of high-Eddington ratio ($λ_\mathrm{Edd}$) active galactic nuclei (AGN) is necessary since the bulk of X-ray spectroscopic studies have been focused on low-Eddington AGN. We present here the X-ray spectral analysis of 14 radio-quiet, $λ_\mathrm{Edd}\gtrsim1$ AGN at $0.4\leq z \leq 0.75$, observed with XMM-Newton. Optical/UV data from simultaneous Optical Monitor observations have been also considered. These AGN have been selected to have relatively high values of black hole mass ($M_\mathrm{BH}\sim10^{8-8.5}M_\odot$) and bolometric luminosity ($L_\mathrm{bol} \sim 10^{46}$ erg s$^{-1}$), in order to complement previous studies of high-Eddington AGN at lower $M_\mathrm{BH}$ and $L_\mathrm{bol}$. We studied the relation between $λ_\mathrm{Edd}$ and other key X-ray spectral parameters, such as the photon index of the power-law continuum $Γ$, the X-ray bolometric correction $k_\mathrm{bol,X}$ and $α_\mathrm{ox}$. Despite the homogeneous optical and SMBH accretion properties, the X-ray properties of these high-Eddington AGN are quite heterogeneous. We measured values of $Γ$ comprised between 1.3 and 2.5, at odds with the expectations based on previously reported $Γ-λ_\mathrm{Edd}$ relations, by which $Γ\geq2$ would be an ubiquitous hallmark of AGN with $λ_\mathrm{Edd}\sim1$. We found that $\sim30\%$ of the sources are X-ray weak, with an X-ray emission about a factor of $\sim10-80$ fainter than that of typical AGN at similar UV luminosities. The X-ray weakness seems to be intrinsic and not due to intervening obscuration. This may indicate that high-Eddington AGN commonly undergo periods of intrinsic X-ray weakness. Furthermore, results from a follow-up monitoring with Swift of one of these X-ray weak AGN suggest that these periods can last for several years.

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arXiv2021

Hunting for the nature of the enigmatic narrow-line Seyfert 1 galaxy PKS 2004-447

Narrow-line Seyfert 1 (NLS1) galaxies are a class of active galactic nuclei (AGN) that, in some cases, can harbor powerful relativistic jets. One of them, PKS 2004-447, shows gamma-ray emission, and underwent its first recorded multifrequency flare in 2019. However, past studies revealed that in radio this source can be classified as a compact steep-spectrum source (CSS), suggesting that, unlike other gamma-ray sources, the relativistic jets of PKS 2004-447 have a large inclination with respect to the line of sight. We present here a set of spectroscopic observations of this object, aimed at carefully measuring its black hole mass and Eddington ratio, determining the properties of its emission lines, and characterizing its long term variability. We find that the black hole mass is $(1.5\pm0.2)\times10^7$ M$_\odot$, and the Eddington ratio is 0.08. Both values are within the typical range of NLS1s. The spectra also suggest that the 2019 flare was caused mainly by the relativistic jet, while the accretion disk played a minor role during the event. In conclusion, we confirm that PKS 2004-447 is one of the rare examples of gamma-ray emitting CSS/NLS1s hybrid, and that these two classes of objects are likely connected in the framework of AGN evolution.

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arXiv2021

Interpreting automatic AGN classifiers with saliency maps

The classification of the optical spectra of active galactic nuclei (AGN) into different types is well founded on AGN physics, but it involves some degree of human oversight and cannot be reliably scaled to large data sets. Machine learning (ML) tackles such a classification problem in a fast and reproducible way, but is often perceived as a black box. However, ML interpretability and explainability are active research areas in computer science, increasingly providing us with tools to alleviate this issue. We applied ML interpretability tools to a classifier trained to predict AGN type from spectra, to demonstrate the use of such tools in this context. We trained a support-vector machine on 3346 high-quality, low redshift AGN spectra from SDSS DR15 with an existing reliable classification as type 1, type 2, or intermediate type. On a selection of test-set spectra, we computed the gradient of the predicted class probability and we built saliency maps. We also visualized the high-dimensional space of AGN spectra using t-distributed stochastic neighbor embedding (t-SNE), showing where the spectra for which we computed a saliency map are located. Regions that affect the predicted AGN type often coincide with physically relevant features, such as spectral lines. t-SNE visualization shows good separability of type 1 and type 2 spectra, while intermediate-type spectra either lie in-between as expected or appear mixed with type 2 spectra. Saliency maps show why a given AGN type was predicted by our classifier, resulting in a physical interpretation in terms of regions of the spectrum that affected its decision, making it no longer a black box. These regions coincide with those used by human experts such as relevant spectral lines, and are even used in a similar way, with the classifier e.g. effectively measuring the width of a line by weighing its center and its tails oppositely.

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arXiv2021

Dark energy constraints from quasar observations

Recent measurements of the parameters of the Concordance Cosmology Model ($Λ$CDM) done in the low-redshift Universe with Supernovae Ia/Cepheids, and in the distant Universe done with Cosmic Microwave Background (CMB) imply different values for the Hubble constant (67.4 $\pm$ 0.5 km s$^{-1}$ Mpc$^{-1}$ from Planck vs 74.03 $\pm$ 1.42 km s$^{-1}$ Mpc$^{-1}$, Riess et al. 2019). This Hubble constant tension implies that either the systematic errors are underestimated, or the $Λ$CDM does not represent well the observed expansion of the Universe. Since quasars - active galactic nuclei - can be observed in the nearby Universe up to redshift z $\sim$ 7.5, they are suitable to estimate the cosmological properties in a large redshift range. Our group develops two methods based on the observations of quasars in the late Universe up to redshift z$\sim $4.5, with the objective to determine the expansion rate of the Universe. These methods do not yet provide an independent measurement of the Hubble constant since they do not have firm absolute calibration but they allow to test the $Λ$CDM model, and so far no departures from this model were found.

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arXiv2020

Selection of highly-accreting quasars: Spectral properties of FeII emitters not belonging to extreme Population A

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. The aim of this paper is to define tight criteria for their proper identification starting from the main selection criterion $R_{FeII} > 1 $, and to identify potential intruders not meeting the selection criteria, but nonetheless selected as xA because of the coarseness of automatic searches. Inclusion of the spurious xA sources may dramatically increase the dispersion in the Hubble diagram of quasars obtained from virial luminosity estimates. We studied a sample of 32 low-$z$ quasars originally selected from the SDSS DR7 as xA. All of them show moderate-to-strong FeII emission and the wide majority strong absorption features in their spectra are typical of fairly evolved stellar populations. We performed a simultaneous fit of a host galaxy spectrum, AGN continuum, FeII template and emission lines to spectra, using the fitting technique based on ULySS, full spectrum fitting package. For sources in our sample (of spectral types corresponding to relatively low Eddington ratio), we found an overall consistency between narrow components of H$β$ and [OIII]$λλ$4959, 5007 line shifts and the mean stellar velocity obtained from the host galaxy fit (within $\lesssim |60|$ km/s). Only one source in our sample qualify as xA source. We found high fraction of host galaxy spectrum (in half of the sample even higher then 40\%). When absorption lines are prominent, and the fraction of the host galaxy is high, SSP is mimicking FeII, and that 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 $R_{FeII}$, and therefore to the misclassification of sources as xA sources.

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arXiv2020

Optical spectral properties of radio loud quasars along the main sequence

We analyze the optical properties of Radio-Loud quasars along the Main Sequence (MS) of quasars. A sample of 355 quasars selected on the basis of radio detection was obtained by cross-matching the FIRST survey at 20cm and the SDSS DR12 spectroscopic survey. We consider the nature of powerful emission at the high-FeII end of the MS. At variance with the classical radio-loud sources which are located in the Population B domain of the MS optical plane, we found evidence indicating a thermal origin of the radio emission of the highly accreting quasars of Population A.

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arXiv2020

The quasar main sequence and its potential for cosmology

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.

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arXiv2020

Extreme quasars as distance indicators in cosmology

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, thanks to selection criteria defined from the systematic changes along the quasars main sequence. It has been possible to build a sample of about 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 AlIII 1860 intermediate ionization line and the Hydrogen Balmer line H-beta as virial broadening estimators, and we briefly discuss the perspective of the method based on xA quasars.

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arXiv2019

Quasar emission lines as virial luminosity estimators

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$β$ as "virial broadening estimators."

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arXiv2019

Radio-loudness along the quasar main sequence

Following the established view of the AGNs inner workings, an AGN is radio-loud (RL) if associated with relativistic ejections emitting a radio synchrotron spectrum (i.e., a jetted AGN). 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 quasar main sequence (MS) and to test whether the condition RK > 10 is sufficient for the identification of RL AGNs. A sample of 355 quasars was selected by cross-correlating the FIRST survey with the SDSS DR14 quasar catalog. We classified the optical spectra according to their spectral types along the quasars MS. For each spectral type, we distinguished compact and extended morphology, and three classes of radio-loudness: detected (specific flux ratio in the g band and at 1.4GHz, RK' < 10, RD), intermediate (10 < RK' < 70, RI), and radio loud (RK' > 70). The analysis revealed systematic differences between RD, RI, and RL in each spectral type along the MS. 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 H-beta 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. The validity of the Kellermann's criterion may be dependent on the source location along the quasar MS. The consideration of the MS trends allowed to distinguish between sources whose radio emission mechanisms is jetted from the ones where the mechanism is likely to be fundamentally different.

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arXiv2019

Black hole mass estimates in quasars - A comparative analysis of high- and low-ionization lines

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$β$ 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$β$. 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$β$ with sample standard deviation ~ 0.3 dex.

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arXiv2019

Quasars: from the Physics of Line Formation to Cosmology

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 radiate at a stable, extreme luminosity-to-mass ratio. This in turns 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 (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.

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arXiv2018

Fe II velocity shifts in optical spectra of type 1 AGN

Here we present a critical view of practical problems in the analysis of optical Fe II emission lines of Type 1 AGN spectra. Besides the very complex and unclear physical interpretation of the Fe II template shape, there are other issues that might affect the results of Fe II contribution as well (like the S/N, the AGN continuum component modelling, the complex shapes of other broad and narrow emission lines that are blending in the same part of the spectrum, the galactic host stellar component that could lead to mimicking of the Fe II template shape on some parts of spectrum, etc.). In this paper we concentrate particularly on the claims of possibility that in some objects Fe II could be strongly shifted to the red. We examine the effects in the fitting procedure that could artificially lead to such results.

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arXiv2018

Extreme quasars at high redshift

Context:Quasars radiating at extreme Eddington ratios (xA) are likely a prime mover of galactic evolution and have been hailed as potential distance indicators. Their properties are still scarcely known. Aims:We 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 UV spectra in the redshift range 2 0.5 and CIII]1909/SiIII]1892<1. The emission line spectra was studied using multicomponent fits of deep spectroscopic observations obtained with the OSIRIS-GTC. Results:Spectra confirm that almost all of these quasars are xA sources with very similar properties. We provide spectrophotometric and line profile measurements for the SiIV1397+OIV]1402, CIV1549+HeII1640, and the 1900A blend composed by AlIII1860, SiIII]1892, FeIII and a weak CIII]1909. The spectra can be characterized as very low ionization (logU~-3), a condition that explains the significant FeIII emission. CIV1549 shows low equivalent width (<30 A for the most sources), and high or extreme blueshift amplitudes (-5000<c(1/2)<-1000 kms-1). Weak-lined quasars appear as extreme xA quasars and not as an independent class. The CIV1549 high amplitude blueshifts coexists in all cases save one with symmetric and narrower AlIII and SiIII] profiles. Estimates of the Eddington ratio using the AlIII FWHM as a virial broadening estimator are consistent with the ones of a previous xA sample. Conclusions:It is now feasible to assemble large samples of xA quasars from the latest data releases of the SDSS. We provide evidence that AlIII1860 could be associated with a low-ionization virialized sub-system, supporting previous suggestions that AlIII is a reliable virial broadening estimator.

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arXiv2018

Highly accreting quasars: The SDSS low-redshift catalog

The most highly accreting quasars (xA) are of special interest in studies of the physics of AGNs and host galaxy evolution. Quasars accreting at high rates (L/LEdd $\sim$ 1) hold promise for use as 'standard candles': distance indicators detectable at very high redshift. However, their observational properties are largely unknown. A large sample of xA can clarify the main properties of quasars radiating near L/LEdd $\sim$ 1 in the Hb spectral range for redshift $\lt$ 0.8. We use selection criteria derived from 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 4570 Å and Hb, RFeII $\gt$ 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. We provide a database of detailed measurements. Analysis of the data allows us to confirm that Hb shows a Lorentzian function with a FWHM of Hb $\lt$ 4000 km s-1. Systematic [OIII] blue shifts, as well as a blueshifted component in Hb are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of Hb is still affected by the blueshifted emission, however, the effect is non-negligible if the FWHM Hb is used as a 'virial broadening estimator'. A effect of the viewing angle on Hb broadening, deriving a correction for those sources that shows disagreement between virial and concordance cosmology luminosity values. The scatter between concordance cosmology and virial luminosity estimates can be reduced if a correction for orientation effects is included in the FWHM Hb value.

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arXiv2018

Narrow-line Seyfert 1s: what is wrong in a name?

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.

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