107 research outputs found
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.Comment: 13 pages, 5 figures. Invited lecture at SPIG 2018, Belgrade. To
appear in Ato
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 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. 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 with sample standard
deviation ~ 0.3 dex.Comment: 43 pages, 15 Figures, submitted to A&
HE0359-3959: an extremely radiating quasar
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 -6000500 km
s 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 figure
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<z<2.9.
Methods:19 extreme quasar candidates were identified using 4DE1 selection
criteria applied to SDSS spectra: AlIII1860/SiIII]1892>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.Comment: 36 pages, 31 figures, 12 tables. Manuscript accepted for publication,
A&A. Corrected titl
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.Comment: 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 201
A main sequence for quasars
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.Comment: Invited talk presented at the Padova Conference on "Quasars at all
cosmic epochs"; to appear in Frontiers of Astrophysics and Space Scienc
Dark energy constraints from quasar observations
Recent measurements of the parameters of the Concordance Cosmology Model
(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 0.5 km s Mpc
from Planck vs 74.03 1.42 km s Mpc, Riess et al. 2019).
This Hubble constant tension implies that either the systematic errors are
underestimated, or the 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 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 z4.5, 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 CDM model, and so far no departures from this model
were found.Comment: 6 pages, 2 figures, contribution to the Proceedings of the 100 years
of the Polish Physical Society Congress, 16-18 October 2020, Warsaw, Poland.
http://info.ifpan.edu.pl/APP
The contribution of financial entities to the sustainable development through the reporting of corporate social responsibility information
This paper aims at examining the relationship between board composition and corporate
social responsibility (CSR) of a sample of listed financial entities, discussing the driving
reasons of these entities to disclose CSR information. We hypothesize that there is a positive
association between outside (institutional and independent directors) and female directors and
CSR disclosure and a negative relationship between inside directors and CSR reporting. Our
findings provide evidence that the proportions of independent directors and female directors
on boards encourage CSR disclosure. Moreover, the results also show that the proportions of
inside directors and institutional directors on boards do not have influence on CSR reporting.
Thus, our evidence suggests that board attributes such as independent and female directors
encourage financial entities to report CSR matters, showing the effectiveness of these two
corporate governance mechanisms. The paper shed light on the influence of board structure of
financial entities on CSR disclosure. Therefore, this study contributes to past research by
providing an index to measure CSR disclosure of financial entities and the importance of the
distinction between outside and inside directors
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.Comment: 5 pages, 2 figures, contribution presented at the IAU Symposium 356,
Nuclear Activity in Galaxies Across Cosmic Time, held in Addis Ababa,
Ethiopia, on Oct. 7-11, 2019. M. Povic et al. (Eds.
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