2,360 research outputs found
On the Column Density of AGN Outflows: the Case of NGC 5548
We re-analyze the HST high resolution spectroscopic data of the intrinsic
absorber in NGC 5548 and find that the C IV absorption column density is at
least four times larger than previously determined. This increase arises from
accounting for the kinematical nature of the absorber and from our conclusion
that the outflow does not cover the narrow emission line region in this object.
The improved column density determination begins to bridge the gap between the
high column densities measured in the X-ray and the low ones previously
inferred from the UV lines. Combined with our findings for outflows in high
luminosity quasars these results suggest that traditional techniques for
measuring column densities: equivalent width, curve-of-growth and Gaussian
modeling, are of limited value when applied to absorption associated with AGN
outflows.Comment: Published ApJ version (566, 699), including a new figure with FUSE
data and a useful algebraic expression for the optical depth solutio
Contrasting the UV and X-ray O VI Column Density Inferred for the Outflow in NGC 5548
We compare X-ray and UV spectroscopic observations of NGC 5548. Both data
sets show O VI absorption troughs associated with the AGN outflow from this
galaxy. We find that the robust lower limit on the column density of the O VI
X-ray trough is seven times larger than the column density found in a study of
the O VI UV troughs. This discrepancy suggests that column densities inferred
for UV troughs of Seyfert outflows are often severely underestimated. We
identify the physical limitations of the UV Gaussian modeling as the probable
explanation of the O VI column density discrepancy. Specifically, Gaussian
modeling cannot account for a velocity dependent covering fraction, and it is a
poor representation for absorption associated with a dynamical outflow.
Analysis techniques that use a single covering fraction value for each
absorption component suffer from similar limitations. We conclude by suggesting
ways to improve the UV analysis.Comment: 16 pages, 1 figure, accepted for publication in Ap
A matrix of interests: Freud, the sexologists, and the legacy of Greece
The use of classical scholarship in nineteenth century debates onsexuality forms the focus of this paper. It is argued that GermanHellenism played a crucial role in providing Freud and Germansexology with a counter discourse to the theory of degeneration, adoctrine that had steadily gained currency in the latter part of thenineteenth century. Sexology and psychoanalysis were contemporaneousareas of investigation that focussed primarily onsexuality and were considered marginalised domains that operatedoutside the scientific establishment of the day. This exclusion wasdue in part to their subject matter, but it was further compounded bytheir widespread rejection of degeneracy, a theory that labelled bothJews and homosexuals as deviant members of society. The complexnetwork of association that existed between psychoanalysis andsexology in Austria and Germany is often neglected and the commonground that they shared is overlooked. This is unfortunate as theyexplored related fields of interest and their members were largelydrawn from similar backgrounds. A significant number of these menwere Jewish, a large number were homosexual or homosocial, andmost of them were excellent classical scholars. Classical studiesprovided the foundation upon which the elite German educationalsystem, the Gymnasium, was built, and while the Gymnasiumcurriculum was designed to inculcate the values of reason, selfdisciplineand idealism, it also allowed an access to the world ofGreek sexuality. It is argued that the divergent attitudes towardssexuality revealed in Greek art and literature provided many of thesesexual pioneers with a legitimate challenge to the medical andpsychiatric definitions of normal and abnormal sexuality
The verifiability approach to deception detection: A preregistered direct replication of the information protocol condition of Nahari, Vrij, and Fisher (2014b)
Jet Acceleration by Tangled Magnetic Fields
We explore the possibility that extragalactic radio jets might be accelerated
by highly disorganized magnetic fields that are strong enough to dominate the
dynamics until the terminal Lorentz factor is reached. Following the
twin-exhaust model by Blandford & Rees (1974), the collimation under this
scenario is provided by the stratified thermal pressure from an external
medium. The acceleration efficiency then depends on the pressure gradient of
that medium. In order for this mechanism to work there must be continuous
tangling of the magnetic field, changing the magnetic equation of state away
from pure flux freezing (otherwise conversion of Poynting flux to kinetic
energy flux is suppressed). This is a complementary approach to models in which
the plasma is accelerated by large scale ordered fields. We include a simple
prescription for magnetic dissipation, which leads to tradeoffs among
conversion of magnetic energy into bulk kinetic energy, random particle energy,
and radiation. We present analytic dynamical solutions of such jets, assess the
effects of radiation drag, and comment on observational issues, such as the
predicted polarization and synchrotron brightness. Finally, we try to make the
connection to observed radio galaxies and gamma-ray bursts.Comment: 15 pages, 10 figures, accepted for publication in Ap
The verifiability approach to deception detection: A preregistered direct replication of the information protocol condition of Nahari, Vrij, and Fisher (2014b)
Functional interplay between NTP leaving group and base pair recognition during RNA polymerase II nucleotide incorporation revealed by methylene substitution.
RNA polymerase II (pol II) utilizes a complex interaction network to select and incorporate correct nucleoside triphosphate (NTP) substrates with high efficiency and fidelity. Our previous 'synthetic nucleic acid substitution' strategy has been successfully applied in dissecting the function of nucleic acid moieties in pol II transcription. However, how the triphosphate moiety of substrate influences the rate of P-O bond cleavage and formation during nucleotide incorporation is still unclear. Here, by employing β,γ-bridging atom-'substituted' NTPs, we elucidate how the methylene substitution in the pyrophosphate leaving group affects cognate and non-cognate nucleotide incorporation. Intriguingly, the effect of the β,γ-methylene substitution on the non-cognate UTP/dT scaffold (∼3-fold decrease in kpol) is significantly different from that of the cognate ATP/dT scaffold (∼130-fold decrease in kpol). Removal of the wobble hydrogen bonds in U:dT recovers a strong response to methylene substitution of UTP. Our kinetic and modeling studies are consistent with a unique altered transition state for bond formation and cleavage for UTP/dT incorporation compared with ATP/dT incorporation. Collectively, our data reveals the functional interplay between NTP triphosphate moiety and base pair hydrogen bonding recognition during nucleotide incorporation
What Determines the Depth of BALs? Keck HIRES Observations of BALQSO 1603+300
We find that the depth and shape of the broad absorption lines (BALs) in
BALQSO 1603+3002 are determined largely by the fraction of the emitting source
which is covered by the BAL flow. In addition, the observed depth of the BALs
is poorly correlated with their real optical depth. The implication of this
result is that abundance studies based on direct extraction of column densities
from the depth of the absorption troughs are unreliable. Our conclusion is
based on analysis of unblended absorption features of two lines from the same
ion (in this case the Si IV doublet), which allows unambiguous separation of
covering factor and optical depth effects. The complex morphology of the
covering factor as a function of velocity suggests that the BALs are produced
by several physically separated outflows. The covering factor is ion dependent
in both depth and velocity width. We also find evidence that in BALQSO
1603+3002 the flow does not cover the broad emission line region.Comment: 13 pages, 2 figures, accepted for publication in Ap
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