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Series

2009

Astrophysics and Astronomy

University of Kentucky

Articles 1 - 12 of 12

Full-Text Articles in Physical Sciences and Mathematics

Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow-Line Region And Near-Nucleus Hot Dust, Rivay Mor, Hagai Netzer, Moshe Elitzur Nov 2009

Dusty Structure Around Type-I Active Galactic Nuclei: Clumpy Torus Narrow-Line Region And Near-Nucleus Hot Dust, Rivay Mor, Hagai Netzer, Moshe Elitzur

Physics and Astronomy Faculty Publications

We fitted Spitzer/IRS ~ 2-35 μm spectra of 26 luminous quasi-stellar objects in an attempt to define the main emission components. Our model has three major components: a clumpy torus, dusty narrow-line region (NLR) clouds, and a blackbody-like dust. The models utilize the clumpy torus of Nenkova et al. and are the first to allow its consistent check in type-I active galactic nuclei (AGNs). Single torus models and combined torus-NLR models fail to fit the spectra of most sources, but three-component models adequately fit the spectra of all sources. We present torus inclination, cloud distribution, covering factor, and …

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Detections Of Water Ice, Hydrocarbons, And 3.3 ΜM Pah In Z ~ 2 Ulirgs, Anna Sajina, Henrik Spoon, Lin Yan, Masatoshi Imanishi, Dario Fadda, Moshe Elitzur Sep 2009

Detections Of Water Ice, Hydrocarbons, And 3.3 ΜM Pah In Z ~ 2 Ulirgs, Anna Sajina, Henrik Spoon, Lin Yan, Masatoshi Imanishi, Dario Fadda, Moshe Elitzur

Physics and Astronomy Faculty Publications

We present the first detections of the 3 μm water ice and 3.4 μm amorphous hydrocarbon (HAC) absorption features in z ~ 2 ULIRGs. These are based on deep rest-frame 2-8 μm Spitzer Infrared Spectrograph spectra of 11 sources selected for their appreciable silicate absorption. The HAC-to-silicate ratio for our z ~ 2 sources is typically higher by a factor of 2-5 than that observed in the Milky Way. This HAC “excess” suggests compact nuclei with steep temperature gradients as opposed to predominantly host obscuration. Beside the above molecular absorption features, we detect the 3.3 μm …

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Rotationally Warm Molecular Hydrogen In The Orion Bar, Gargi Shaw, Gary J. Ferland, W. J. Henney, P. C. Stancil, N. P. Abel, E. W. Pellegrini, J. A. Baldwin, P. A. Van Hoof Aug 2009

Rotationally Warm Molecular Hydrogen In The Orion Bar, Gargi Shaw, Gary J. Ferland, W. J. Henney, P. C. Stancil, N. P. Abel, E. W. Pellegrini, J. A. Baldwin, P. A. Van Hoof

Physics and Astronomy Faculty Publications

The Orion Bar is one of the nearest and best-studied photodissociation or photon-dominated regions (PDRs). Observations reveal the presence of H2 lines from vibrationally or rotationally excited upper levels that suggest warm gas temperatures (400-700 K). However, standard models of PDRs are unable to reproduce such warm rotational temperatures. In this paper, we attempt to explain these observations with new comprehensive models which extend from the H+ region through the Bar and include the magnetic field in the equation of state. We adopt the model parameters from our previous paper which successfully reproduced a wide variety of spectral …

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The Ionization Balance Of A Non-Equilibrium Plasma, Gary J. Ferland Jun 2009

The Ionization Balance Of A Non-Equilibrium Plasma, Gary J. Ferland

Physics and Astronomy Faculty Publications

Commentary on: Arnaud M. and Rothenflug R., 1985, A&AS, 60, 425.

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Orion's Bar: Physical Conditions Across The Definitive H+/H0/H2 Interface, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland, G. Shaw, S. Heathcote Mar 2009

Orion's Bar: Physical Conditions Across The Definitive H+/H0/H2 Interface, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland, G. Shaw, S. Heathcote

Physics and Astronomy Faculty Publications

Previous work has shown the Orion Bar to be an interface between ionized and molecular gas, viewed roughly edge-on, which is excited by the light from the Trapezium cluster. Much of the emission from any star-forming region will originate from such interfaces, so the Bar serves as a foundation test of any emission model. Here we combine X-ray, optical, infrared (IR), and radio data sets to derive emission spectra along the transition from H+ to H0 to H2 regions. We then reproduce the spectra of these layers with a simulation that simultaneously accounts for the detailed microphysics …

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Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland Feb 2009

Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland

Physics and Astronomy Faculty Publications

Nonionizing stellar continua are a potential source of photons for continuum pumping in the hydrogen Lyman transitions. In the environments where these transitions are optically thick, de-excitation occurs through higher series lines. As a result, the emitted flux in the affected lines has a fluorescent contribution in addition to the usual recombination one; in particular, Balmer emissivities are systematically enhanced above case B predictions. The effectiveness of such a mechanism in H II regions and the adequacy of photoionization models as a tool to study it are the two main focuses of this work. We find that photoionization models of …

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Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland Jan 2009

Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland

Physics and Astronomy Faculty Publications

Signatures of warm absorbers are seen in soft X-ray spectra of about half of all type 1 Seyfert galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular, we find the following results: (i) the warm absorber exists only if the spectral index …

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The Three-Dimensional Dynamic Structure Of The Inner Orion Nebula, C. R. O'Dell, W. J. Henney, N. P. Abel, Gary J. Ferland, S. J. Arthur Jan 2009

The Three-Dimensional Dynamic Structure Of The Inner Orion Nebula, C. R. O'Dell, W. J. Henney, N. P. Abel, Gary J. Ferland, S. J. Arthur

Physics and Astronomy Faculty Publications

The three-dimensional structure of the brightest part of the Orion Nebula is assessed in the light of published and newly established data. We find that the widely accepted model of a concave blister of ionized material needs to be altered in the southwest direction from the Trapezium, where we find that the Orion-S feature is a separate cloud of very optically thick molecules within the body of ionized gas, which is probably the location of the multiple embedded sources that produce the optical and molecular outflows that define the Orion-S star formation region. Evidence for this cloud comes from the …

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Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan Jan 2009

Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan

Physics and Astronomy Faculty Publications

Effective collision strengths for forbidden transitions among the five energetically lowest fine-structure levels of O II are calculated in the Breit–Pauli approximation using the R-matrix method. Results are presented for the electron temperature range 100–100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O II ratio, a matter of some …

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Collisional Heating As The Origin Of Filament Emission In Galaxy Clusters, G. J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams Jan 2009

Collisional Heating As The Origin Of Filament Emission In Galaxy Clusters, G. J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams

Physics and Astronomy Faculty Publications

It has long been known that photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. This paper builds on the first of this series in which we examined whether heating by energetic particles or dissipative magnetohydrodynamic (MHD) wave can account for the observations. The first paper focused on the molecular regions which produce strong H2 and CO lines. Here we extend the calculations to include atomic and low-ionization regions. Two major improvements to the previous calculations have been made. The model …

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The Location And Kinematics Of The Coronal-Line Emitting Regions In Active Galactic Nuclei, J. R. Mullaney, M. J. Ward, C. Done, Gary J. Ferland, N. Schurch Jan 2009

The Location And Kinematics Of The Coronal-Line Emitting Regions In Active Galactic Nuclei, J. R. Mullaney, M. J. Ward, C. Done, Gary J. Ferland, N. Schurch

Physics and Astronomy Faculty Publications

We use the photoionization code CLOUDY to determine both the location and the kinematics of the optical forbidden, high-ionization line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km s …

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Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey Jan 2009

Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey

Physics and Astronomy Faculty Publications

A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyse and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call ‘optimistic’ and ‘pessimistic’. We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H IIregions and the epoch of cosmological recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than …

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