160 research outputs found
Quasars in the 4D Eigenvector 1 Context: A stroll down memory lane
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.Comment: 27 pages, 6 figure
Highly Accreting Quasars: Sample Definition and Possible Cosmological Implications
We propose a method to identify quasars radiating closest to the Eddington
limit, defining primary and secondary selection criteria in the optical, UV and
X-ray spectral range based on the 4D eigenvector 1 formalism. We then show that
it is possible to derive a redshift-independent estimate of luminosity for
extreme Eddington ratio sources. Using preliminary samples of these sources in
three redshift intervals (as well as two mock samples), we test a range of
cosmological models. Results are consistent with concordance cosmology but the
data are insufficient for deriving strong constraints. Mock samples indicate
that application of the method proposed in this paper using dedicated
observations would allow to set stringent limits on Omega_M and significant
constraints on Omega_Lambda.Comment: Accepted for publication in MNRA
The Quasar Main Sequence explained by the combination of Eddington ratio, metallicity and orientation
We address the effect of orientation of the accretion disk plane and the
geometry of the broad-line region (BLR) as part of an effort to understand the
distribution of quasars in the optical plane of the quasar main sequence. We
utilize the photoionization code CLOUDY to model the BLR incorporating the
grossly underestimated form factor (). Treating the aspect of viewing angle
appropriately, we confirm the dependence of the sequence on
Eddington ratio and on the related observational trends - as a function of the
SED shape, cloud density and composition, verified from prior observations.
Sources with in the range 1 -- 2 (about 10\% of all
quasars, the so-called extreme Population A [xA] quasars) are explained as
sources of high, and possibly extreme Eddington ratio along the
sequence. This result has important implication for the
exploitation of xA sources as distance indicators for Cosmology.
emitters with are very rare (<1\% of
all type 1 quasars). Our approach also explains the rarity of these highest
emitters as extreme xA sources and constrains the viewing angle
ranges with increasing H FWHM.Comment: 9 pages, 4 figures, 1 table; accepted for publication in Ap
The transformation of Spirals into S0 galaxies in the cluster environment
We discuss the observational evidences of the morphological transformation of
Spirals into S0 galaxies in the cluster environment exploiting two big
databases of galaxy clusters: WINGS (0.04 < z < 0.07) and EDisCS (0.4 < z <
0.8). The most important results are: 1) the average number of S0 galaxies in
clusters is almost a factor of larger today than at redshift ; 2) the fraction of S0's to Spirals increases on average by a factor
2 every Gyr; 3) the average rate of transformation for Spirals (not
considering the infall of new galaxies from the cosmic web) is: 5 Sp
into S0's per Gyr and 2 Sp into E's per Gyr; 4) there are evidences that
the interstellar gas of Spirals is stripped by an hot intergalactic medium; 5)
there are also indirect hints that major/minor merging events have played a
role in the transformation of Spiral galaxies. In particular, we show that: 1)
the ratio between the number of S0's and Spirals (NS0/NSp) in the WINGS
clusters is correlated with their X-ray luminosity ; 2) that the
brightest and massive S0's are always close to the cluster center; 3) that the
mean Sersic index of S0's is always larger than that of Spirals (and lower than
E's) for galaxy stellar masses above Msun; 4) that the number of E's
in clusters cannot be constant; 5) that the largest difference between the mean
mass of S0's and E's with respect to Spirals is observed in clusters with low
velocity dispersion. Finally, by comparing the properties of the various
morphological types for galaxies in clusters and in the field, we find that the
most significant effect of the environment is the stripping of the outer galaxy
regions, resulting in a systematic difference in effective radius and Sersic
index.Comment: 38 pages, 20 figure
The Powerful Jet and Gamma-Ray Flare of the Quasar PKS 0438436
PKS 0438436 at a redshift of has been previously recognized as
possessing perhaps the most luminous known synchrotron jet. Little is known
about this source since the maximum elevation above the horizon is low for the
Very Large Array (VLA). We present the first VLA radio image that detects the
radio lobes. We use both the 151 MHz luminosity, as a surrogate for the
isotropic radio lobe luminosity, and the lobe flux density from the radio image
to estimate a long term, time averaged, jet power, . We analyze two deep optical spectra with
strong broad emission lines and estimate the thermal bolometric luminosity of
the accretion flow, . The ratio, , is at
the limit of this empirical metric of jet dominance seen in radio loud quasars
and this is the most luminous accretion flow to have this limiting behavior.
Despite being a very luminous blazar, it previously had no -ray
detections (EGRET, AGILE or FERMI) until December 11 - 13 2016 (54 hours) when
FERMI detected a flare that we analyze here. The isotropic apparent luminosity
from 100 MeV - 100 GeV rivals the most luminous detected blazar flares
(averaged over 18 hours), . The
-ray luminosity varies over time by two orders of magnitude,
highlighting the extreme role of Doppler abberation and geometric alignment in
producing the inverse Compton emission.Comment: To appear in ApJ. Revision required to replace the last figure file
with the current versio
Gravitational Redshift of Emission Lines in the AGN Spectra
The detection of gravitationally redshifted optical emission lines has been
reported just for a few active galaxies. In this paper we give a short overview
of studies that analyzed or exploited the detection of the gravitational
redshift in optical AGN spectra. In addition, we tested the consistency of
gravitational redshift as the physical origin of the redward shifts observed in
their spectra using a sample of 50 Hamburg-ESO intermediate to high
redshift quasars that are among the most luminous quasars known ( erg/s), and are expected to host very massive
black holes. To this aim we modeled the line profile with accretion disk models
around a black hole.Comment: 10 pages, 2 figures, 3 table
- …