992 research outputs found
3C 57 as an Atypical Radio-Loud Quasar: Implications for the Radio-Loud/Radio-Quiet Dichotomy
Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the
4D Eigenvector 1 (4DE1) parameter space which implies restricted
geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ)
majority of quasars. We discuss how this restricted domain for the LD RL parent
population supports the notion for a RQ-RL dichotomy among Type 1 sources. 3C
57 is an atypical RL quasar that shows both uncertain radio morphology and
falls in a region of 4DE1 space where RL quasars are rare.
We present new radio flux and optical spectroscopic measures designed to
verify its atypical optical/UV spectroscopic behaviour and clarify its radio
structure. The former data confirms that 3C 57 falls off the 4DE1 quasar "main
sequence" with both extreme optical FeII emission (R_{FeII} ~ 1) and a large
CIV 1549 profile blueshift (~ -1500 km/s). These parameter values are typical
of extreme Population A sources which are almost always RQ. New radio measures
show no evidence for flux change over a 50+ year timescale consistent with
compact steep-spectrum (CSS or young LD) over core-dominated morphology. In the
4DE1 context where LD RL are usually low L/L_{Edd} quasars we suggest that 3C
57 is an evolved RL quasar (i.e. large Black Hole mass) undergoing a major
accretion event leading to a rejuvenation reflected by strong FeII emission,
perhaps indicating significant heavy metal enrichment, high bolometric
luminosity for a low redshift source and resultant unusually high Eddington
ratio giving rise to the atypical CIV 1549.Comment: Accepted for publication in MNRAS; 10 pages, 6 figures, 4 table
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 Intermediate Line Region in AGN: a region "praeter necessitatem"?
As a consequence of improved S/N, spectral resolution and wavelength coverage
various authors have introduced, without strong justification, new emitting
regions to account for various emission line profile differences in AGN. The
so-called CIVlambda1549 intermediate line region (ILR) appears to be especially
ill-defined. We present observational evidence that suggests the ILR is
statistically indistinguishable from the classical narrow line region (NLR). We
present the results of theoretical models showing that a smooth density
gradient in the NLR can produce CIV and Balmer emission lines with different
widths. The putative ILR component has often been included with the broad line
profile in studies of CIV BLR properties. Failure to account for the composite
nature of CIV emission, and for the presence of sometimes appreciable NLR CIV
emission, has important consequences for our understanding of the BLR.Comment: 3 Figs. 1 Table, accepted for publication in Astrophysical Journal
Letter
The double nucleus galaxies Mkn 423 and Mkn 739
Long slit spectroscopy and imaging of Mkn 423 and Mkn 739 were performed on the 2.2 m and 3.5 m telescopes of the Calar Alto Observatory using both change coupled device (CCD) and photographic detectors. Low and medium resolution spectra (1.8A, 3.5A, 6.0A) together with V images have permitted the demonstration of the merging nature of Mkn 423 and the double structure of the narrow line region (NLR) of its Seyfert component. This last feature has been found also in the NLR of the Seyfert component of Mkn 739, a double system the two components of which are counterrotating
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
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