Fractal Quasar Clouds

This paper examines whether a fractal cloud geometry can reproduce the emission-line spectra of active galactic nuclei (AGNs). The nature of the emitting clouds is unknown, but many current models invoke various types of magnetohydrodynamic confinement. Recent studies have argued that a fractal distribution of clouds, in which subsets of clouds occur in self-similar hierarchies, is a consequence of such confinement. Whatever the confinement mechanism, fractal cloud geometries are found in nature and may be present in AGNs too. We first outline how a fractal geometry can apply at the center of a luminous quasar. Scaling laws are derived that establish the number of hierarchies, typical sizes, column densities, and densities. Photoionization simulations are used to predict the integrated spectrum from the ensemble. Direct comparison with observations establishes all model parameters so that the final predictions are fully constrained. Theory suggests that denser clouds might form in regions of higher turbulence and that larger turbulence results in a wider dispersion of physical gas densities. An increase in turbulence is expected deeper within the gravitational potential of the black hole, resulting in a density gradient. We mimic this density gradient by employing two sets of clouds with identical fractal structuring but different densities. The low-density clouds have a lower column density and large covering factor similar to the warm absorber. The high-density clouds have high column density and smaller covering factor similar to the broad-line region (BLR). A fractal geometry can simultaneously reproduce the covering factor, density, column density, BLR emission-line strengths, and BLR line ratios as inferred from observation. Absorption properties of the model are consistent with the integrated line-of-sight column density as determined from observations of X-ray absorption, and when scaled to a Seyfert galaxy, the model is consistent with the number of multiple UV absorption components observed in them. Rough estimates show that about one in 100 of the galaxies that harbor a supermassive black hole will show activity, assuming that material needs to be within its EUV continuum emitting radius for activity to occur. This is close to the observationally determined duty cycle. Stochastic feeding of the central engine of fractal cloud distribution of material may therefore account for continuum variations and long-term activity. The total cloud mass is much larger than that measured in ionized gas alone since the clouds are mutually self-shielding

Dissipative Heating and Quasar Emission Lines

Recent observations reveal that the profiles of emission lines of active galactic nuclei are too smooth to be produced by discrete thermal (T~104 K) clouds. The lines may also be too bright to be powered by the continuum unless a large covering factor or additional heating mechanisms are present. We have been investigating one possible explanation of these observations, namely, that the clouds are turbulent. This paper focuses on observational effects caused by dissipation of turbulent energy into cloud heating. We find that internal heating can explain these observations. Clouds energized by both the ionizing continuum and dissipative heating are more efficient line emitters than those powered by the continuum alone. The turbulent velocity field broadens the emission contributions of individual line-emitting clouds so that they overlap, smoothing the line profile. We have broad success in reproducing the observed emission-line spectrum with a turbulent velocity of ~200 km s-1, a cloud density of 1010 cm-3, and a column density of 1022 cm-2. Dissipative turbulence selectively increases intensities of low-ionization lines, making it possible to obtain the standard\u27\u27 broad-line region line spectrum with a column density ~10 times smaller than usually assumed. The presence of dissipative heating could explain two long-standing puzzles in quasar emission-line spectra, namely, the smooth line profiles and the energetics of the spectrum

Magnetic Confinement, Magnetohydrodynamic Waves and Smooth Line Profiles in Active Galactic Nuclei

In this paper, we show that if the broad-line region clouds are in approximate energy equipartition between the magnetic field and gravity, as hypothesized by Rees, there will be a significant effect on the shape and smoothness of broad emission-line profiles in active galactic nuclei. Linewidths of contributing clouds or flow elements are much wider than their thermal widths, because of the presence of non-dissipative magnetohydrodynamic waves and their collective contribution produce emission-line profiles broader and smoother than would be expected if a magnetic field were not present. As an illustration, a simple model of isotropically emitting clouds, normally distributed in velocity, is used to show that smoothness can be achieved for less than ∼8×104 clouds and may even be as low as a few hundred. We conclude that magnetic confinement has far-reaching consequences for observing and modelling active galactic nuclei

Healthcare professionals’ perceptions of risk in the context of genetic testing for the prediction of chronic disease: a qualitative metasynthesis

Advances in genomic technologies and a growing trend towards stratified and preventive approaches to medicine mean that increasing numbers of individuals may have access to information about their genetic makeup, and their risk of developing diseases. This is likely to impact on healthcare professionals involved in the delivery of genetic tests, or in supporting patients who are affected by a disease with a genetic risk factor. It is therefore important to understand health-care professionals’ perceptions about providing these services, and how they feel about communicating information about genetic risk to patients. This paper provides a systematic review and metasynthesis of qualitative research exploring healthcare professionals’ perceptions of genetic risk in the context of predictive genetic testing for chronic disease. Healthcare professionals expressed a range of reservations about the utility of predictive testing in this context. Professionals judged patients’ understanding of risk information to be limited and subject to bias and a range of sociocultural influences. Concerns about the psychosocial impact of genetic risk information were frequently cited, both in relation to individual patients and the wider impact on their families and communities. The need for provision of multidisciplinary support was described. The concept of responsibility was also an important theme. Healthcare professionals recognized the responsibility that accompanies risk knowledge, and that ultimately this responsibility lies with the patient, not the provider. Our analysis suggests that professionals’ evaluation of the utility of predictive genetic testing is influenced not only by resource deficits, but may also be interpreted as a response to challenging ethical and social issues associated with genetic risk, that are not well aligned with current medical practice

Magnetic Confinement, MHD Waves, and Smooth Line Profiles in AGN

In this paper, we show that if the broad line region clouds are in approximate energy equipartition between the magnetic field and gravity, as hypothesized by Rees, there will be a significant effect on the shape and smoothness of broad emission line profiles in active galactic nuclei. Line widths of contributing clouds or flow elements are much wider than their thermal widths, due to the presence of non-dissipative MHD waves, and their collective contribution produce emission line profiles broader and smoother than would be expected if a magnetic field were not present. As an illustration, a simple model of isotropically emitting clouds, normally distributed in velocity, is used to show that smoothness can be achieved for less than 80,000 clouds and may even be as low as a few hundred. We conclude that magnetic confinement has far reaching consequences for observing and modeling active galactic nuclei.Comment: to appear in MNRA

Observational Constraints on the Internal Velocity Field of Quasar Emission-Line Clouds

This paper addresses the question, what does the spectrum of a typical quasar reveal about the velocity structure within its broad emission line region clouds? Turbulent (i.e., nonthermal) broadening of spectral lines can be due to macroturbulence or microturbulence. Microturbulence affects line formation and the emitted spectrum and may be required to account for the observed smoothness of the line profiles. The velocity field is crucial since it addresses the fundamental nature of the individual clouds and the global structure of the active galactic nuclei (AGNs) environment. For example, stellar winds or magnetically confined blobs might be highly microturbulent, requiring only a few internally broadened clouds to account for the observed smooth line profiles in AGNs. On the other hand, clouds in pressure confinement would have only thermal line widths, requiring many clouds moving in a large-scale velocity field to achieve the same effect. There are almost no previous studies of the effects of microturbulence, even though the observation that AGN lines are very smooth seems to require additional line broadening mechanisms. We present a broad range of photoionization calculations in which the microturbulence is varied between 0 km s-1 (thermal broadening only) and 104 km s-1, an upper limit set by the observed line width. In general, the line spectrum grows stronger relative to the continuum as turbulence increases. This is because lines more easily escape due to diminished line optical depth and permitted lines are selectively strengthened by continuum pumping. Comparisons with observations reveal two cases. The predicted relative intensities of the majority of the strong lines in typical objects do not depend strongly on the microturbulent field. A turbulence of ~103 km s-1 does not violate observations, but is not required either. However, in the sharp-lined quasars, some lines require a turbulence of the same order as the observed line width to reproduce the spectrum

On the Effects of Dissipative Turbulence on the Narrow Emission-Line Ratios in Seyfert Galaxies

We present a photoionization model study of the effects of micro-turbulence and dissipative heating on emission lines for number and column densities, elemental abundances, and ionizations typical for the narrow emission line regions (NLRs) of Seyfert galaxies. Earlier studies of NLR spectra generally found good agreement between the observations and the model predictions for most strong emission lines, such as [O III] $\lambda$5007, [O II] $\lambda$3727, [N II] $\lambda$6583, [Ne III] $\lambda$3869, and the H and He recombination lines. Nevertheless, the strengths of lines from species with ionization potentials greater than that of He$^{+}$(54.4 eV), e.g. N$^{+4}$ and Ne$^{+4}$, were often under-predicted. Among the explanations suggested for these discrepancies were (selectively) enhanced elemental abundances and contributions from shock heated gas. Interestingly, the NLR lines have widths of several 100 km s$^{-1}$, well in excess of the thermal broadening. If this is due to micro-turbulence, and the turbulence dissipates within the emission-line gas, the gas can be heated in excess of that due to photoionization. We show that the combined effects of turbulence and dissipative heating can strongly enhance N V $\lambda$1240 (relative to He II $\lambda$1640), while the heating alone can boost the strength of [Ne V] $\lambda$3426. We suggest that this effect is present in the NLR, particularly within $\sim$ 100 pc of the central engine. Finally, since micro-turbulence would make clouds robust against instabilities generated during acceleration, it is not likely to be a coincidence that the radially outflowing emission-line gas is turbulent.Comment: 29 oages, including 10 figures. Accepted for publication in the Astrophysical Journa

H-beta Line Width and the UV-X-ray Spectra of Luminous AGN

The width of the broad H-beta emission line is the primary defining characteristic of the NLS1 class. This parameter is also an important component of Boroson and Green's optical Eigenvector 1 (EV1), which links steeper soft X-ray spectra with narrower H-beta emission, stronger H-beta blue wing, stronger optical Fe II emission, and weaker [O III] lambda 5007. Potentially, EV1 represents a fundamental physical process linking the dynamics of fueling and outflow with the accretion rate. We attempted to understand these relationships by extending the optical spectra into the UV for a sample of 22 QSOs with high quality soft-X-ray spectra, and discovered a whole new set of UV relationships that suggest that high accretion rates are linked to dense gas and perhaps nuclear starbursts. While it has been argued that narrow (BLR) H-beta means low Black Hole mass in luminous NLS1s, the C IV, lambda 1549 and Ly alpha emission lines are broader, perhaps the result of outflows driven by their high Eddington accretion rates. We present some new trends of optical-UV with X-ray spectral energy distributions. Steeper X-ray spectra appear associated with stronger UV relative to optical continua, but the presence of strong UV absorption lines is associated with depressed soft X-rays and redder optical-UV continua.Comment: Invited talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

Effect of Corn Type and Form of Supplement on Grazing Steers

Eighty stocker steers were grazed on bromegrass from April to the beginning of November and were provided five different feeds while on grass during the summer. Treatments evaluated included (1) mineral only; (2) free-choice supplementation in the form of liquid feed (MIX30) or (3) block format (Mintrate 40 Red); and hand-fed supplements of 60% corn:40% dried distillers grains at 0.5% of body weight on a dry matter basis offered daily where the corn was either an (4) isoline corn (ISO; parent genetic line) or (5) Enogen feed corn (ENO; includes alpha-amylase gene). Steers were weighed every 28 days while on grass and were carcass quality measured by ultrasound prior to placement in the feedlot. Hand-fed steers had greater gain than self-fed supplemented steers and these steers also had more backfat and tended to have more muscle depth coming off grass than other supplemented steers. Steers that received free-choice mineral or self-fed supplements also had lower gains than steers being hand-fed supplement. Within the first 28 days of the study, the hand-fed steers began weighing more and weighed 125 pounds more than the free-choice supplemented and control steers. On average hand-fed steers had a 0.6 lb/d greater ADG than control steers and those consuming free-choice supplement. Cost of gain was the highest with hand-fed steers at $0.27/pound, but even so profit was greatest with the hand-fed cattle

Complex X-ray Absorption and the Fe Kalpha Profile in NGC 3516

We present data from simultaneous Chandra, XMM-Newton and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and Nov. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating data show the presence of X-ray absorption lines, revealing two distinct components of the absorbing gas, one which is consistent with our previous model of the UV/X-ray absorber while the other, which is outflowing at a velocity of ~1100 km/s has a larger column density and is much more highly ionized. The broad-band spectral characteristics of the X-ray continuum observed with XMM during 2001 April, reveal the presence of a third layer of absorption consisting of a very large column (~2.5 x 10E23 cm^-2) of highly ionized gas with a covering fraction ~50%. This low covering fraction suggests that the absorber lies within a few lt-days of the X-ray source and/or is filamentary in structure. Interestingly, these absorbers are not in thermal equilibrium with one another. The two new components are too highly ionized to be radiatively accelerated, which we suggest is evidence for a hydromagnetic origin for the outflow. Applying our model to the Nov dataset, we can account for the spectral variability primarily by a drop in the ionization states of the absorbers, as expected by the change in the continuum flux. When this complex absorption is accounted for we find the underlying continuum to be typical of Seyfert 1 galaxies. The spectral curvature attributed to the high column absorber, in turn, reduces estimates of the flux and extent of any broad Fe emission line from the accretion disk.Comment: 33 pages, 9 figures, accepted for publication in Ap