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At least 145 records · Page 8
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NASA NTRS1976

The effect of suprathermal protons on the physical conditions in Seyfert galaxy nuclei. II

Radiative transfer of Ly-alpha, Ly-beta, and H-alpha in a hydrogen gas containing dust is considered with application to the emitting gas in Seyfert galaxies. The line radiation originates from the kinetic energy of suprathermal particles lost initially to a free-electron gas, which then delivers it to the radiation through excitation of neutral hydrogen atoms. By neglecting the direct escape of line radiation and by averaging over the gas, transfer in space is suppressed, and only transfer in frequency is considered. The dust degrades the line radiation via frequency-independent absorption, converting the energy to infrared luminosity. Solutions are obtained for the source functions in the lines, using appropriate approximations, in order to determine under what conditions the narrow component of the Balmer-line radiation from the gas can be self-absorbed and degraded without similar degradation of the broad component, which originates from the suprathermals themselves. The results of the transfer calculation are employed to find self-consistent values for the temperature and ionization of the gas for various amounts of dust and various concentrations of suprathermal particles. The luminosity in the Balmer continuum is examined which would result under these conditions.

Stoner, R.↗
NASA NTRS1977

The origin of the broad line emission from Seyfert galaxies

Mass loss from an accretion disk around a supermassive (of the order of 100 million solar masses) black hole is proposed as the origin of the broad permitted lines of Seyfert galaxies and QSOs. The material is expelled by ionizing radiation emitted near the center of the disk and striking it at a radius of approximately 10 to the 16.5 power cm. The escaping gas initially has a density of about 1 trillion per cu cm, high enough for radiation pressure to accelerate the gas to high radial velocities. The model leads to line emission from tiny dense filaments moving at about 10,000 km/s in a region roughly 10 to the 17th power cm across. This agrees with the observed broad line widths, variability time scales, and the absence of broad forbidden-line emission.

Shields, G. A.↗
NASA NTRS1975

The effect of suprathermal protons on the physical conditions in Seyfert galaxy nuclei II

The radiative transfer of Ly-alpha, Ly-beta, and H-alpha in a hydrogen gas containing dust was considered with application to the nuclear gas in Seyfert galaxies. By neglecting the direct escape of line radiation and by averaging over the gas, the radiation transfer in space is suppressed and the frequency transfer only is considered. The dust degrades the line radiation via frequency-independent absorption, converting the energy to infrared luminosity. The source functions in the lines were solved, using appropriate approximations, in order to determine under what conditions the narrow component of the Balmer line radiation from the gas can be self-absorbed and degraded without similar degradation of the broad component, which originates from the suprathermals themselves. The results are used to find self-consistent values for the temperature and ionization of the gas for various amounts of dust and various concentrations of suprathermal particles.

Stoner, R.↗
NASA NTRS1995

Extended soft X-ray emission in Seyfert galaxies: ROSAT HRI observations of NGC 3516, NGC 4151, and Markarian 3

We have used the ROSAT High Resolution Imager (HRI) to examine the distribution of soft X-rays in three nearby Seyfert galaxies with approximately 4 to 5 arcsecs FWHM spatial resolution. A feature of our analysis is an attempt to remove errors in the aspect solution using a method developed by one of us (J.M.). NGC 4151 shows resolved X-ray emission that is spatially correlated with the optical extended narrow-line region (ENLR), confirming the results obtained with the Einstein HRI by Elvis, Briel, & Henry. NGC 3516 is elongated along a position angle of approximately 40 to 220 deg, similar to the direction of the Z-shaped narrow-line region. MRK 3 is very faint in our HRI image and is probably spatially unresolved. We detect the faint X-ray source approximately 2 arcmins west of the MRK 3 nucleus previously found by Turner, Urry, & Mushotzky. We also detected the BL Lac object BL 1207 + 39 approximately 5 arcmins north-northwest of NGC 4151. This object appears spatially unresolved, but some excess X-ray emission may be observed in the azimuthally averaged radial brightness profile of BL 1207 + 39 between radii of 10 arcsecs and 30 arcsecs when compared to a calibration source. A much deeper image is necessary to confirm this result.

Morse, Jon A.↗
NASA NTRS1983

Prominent ultraviolet emission lines from Type 1 Seyfert galaxies

IUE Explorer data with a 6-A resolution are reported for Ly-alpha, C IV 1550 A, C III semiforbidden line 1909 A, and Mg II 2800 A, as well as the continuum at 1450 A, for 20 Seyfert galaxies and one quasar. Good correlation is found between the continuum and the line fluxes, indicating that photoionization is the dominant heating mechanism for these active galactic nuclei. A combination of the data for Seyferts and high redshift quasars covering five orders of magnitude in continuum luminosity shows the lower luminosity objects to have higher equivalent widths for their emission lines, suggesting that the covering factor increases with decreasing luminosity.

Wu, C.-C.↗
NASA NTRS1985

Seyfert galaxy narrow-line regions. I - Observations of forbidden O III lambda 5007

High-resolution (23 km/s) spectra of the forbidden O III emission line at 500.7 nm from the nuclear regions of 32 Seyfert galaxies and low-redshift QSOs have been obtained at the Smithsonian Institution/University of Arizona Multiple Mirror Telescope. The properties of the data are summarized by a group of measures which efficiently describe the entire line profiles, are stable in the presence of noise, and have easily visualized geometric meaning. The distributions of line profile measures are shown. In particular, typical forbidden O III FWHM values of 200-520 km/s (mean + or - 1 sigma) and a highly significant tendency for the lines to fall off more slowly on the blue than on the red side of the peak have been found, in agreement with previous work. Using galaxian system velocities obtained from absorption-line measurements, the distribution of differences between forbidden O III emission-line velocities and galaxian system velocities has been determined; in disagreement with previous work, this distribution has been found to be consistent with symmetry about zero difference velocity.

Vrtilek, J. M.↗
NASA NTRS1986

The radio source in the very luminous gamma-ray Seyfert galaxy MCG 8-11-11

VLA high resolution observations of the Seyfert 1.5 galaxy MCG 8-11-11 at 2 and 6 cm show the center of the galaxy to contain a triple radio source of 400 pc, with a less than 30-pc diameter central component that may be identified as the center of the galaxy. The triple source is in turn embedded in more diffuse emission which has a major axis position angle similar to that in the optical galaxy, but differing from the position angle of the triple source by 50 deg. While the overall morphology of the source is S-shaped, the curvature of the triple source at the ends is abrupt rather than continuous and gradual. It appears that the core radio emission in Seyfert 1 and 1.5 galaxies may be weakly correlated with their X-ray emission.

Ulvestad, J. S.↗
NASA NTRS1980

The Penrose Photoproduction Scenario for NGC 4151 /PCS-SSC/ - A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies

On the basis of general arguments, it has been suggested (Bignami et al., 1979) that a steepening of the spectrum between X-ray and gamma-ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma-ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. It is shown that the above suggestion can be given a consistent theoretical interpretation in the context of the Penrose Photoproduction Scenario (PCS-SSC). Specifically in the case of NGC 4151, the dominant process will be shown to be Penrose Compton Scattering PCS in the ergosphere of a massive, central, rapidly spinning Kerr black hole, assumed in its nucleus. It is assumed that PCS gamma-ray induced electron-position, Synchrotron-Self-Compton processes 'evolve' as the dominant source of nonthermal X-rays.

Leiter, D.↗
NASA NTRS1985

X-ray luminosity and the hydrogen-line ratios of quasars and Seyfert galaxies

New observations of the Ly-alpha/H-alpha ratio in a set of X-ray-selected active galactic nuclei and an archival study of International Ultraviolet Explorer (IUE) observations of Ly-alpha in low-redshift quasars and Seyfert galaxies have been used to form a large sample (49 objects) for studying the influence of soft X-rays on the enhancement of Balmer emission in the broad-line region. In common models of broad-line clouds, the Balmer lines are formed deep in the interior, largely by collisional excitation. Heating within the clouds is provided by soft X-ray radiation, while Ly-alpha is formed mainly by recombination after photoionization. The ratio Ly-alpha/H-alpha is expected to depend weakly on the ratio of ionizing ultraviolet luminosity to X-ray luminosity, L(UV)/L(x). If the Ly-alpha luminosity is used as a measure of L(UV), a weak dependence of Ly-alpha/H-alpha on the X-ray luminosity is found (valid at the 94 percent confidence level), similar to previous results. Future definitive studies depend more critically on contemporaneous observations and better internal reddening estimates rather than a larger sample size.

Kriss, G. A.↗
NASA NTRS1984

Hydrogen line ratios in Seyfert galaxies and low redshift quasars

New observations of the Lymal alpha radiation/hydrogen alpha radiation ratio in a set of X-ray selected active galactic nuclei and an archival study of International Ultraviolet Explorer (IUE) observations of Lymal alpha low redshift quasars and Seyfert galaxies have been used to form a large sample for studying the influence of soft X-rays on the enhancement of Balmer emission in the broad line region. In common models of broad line clouds, the Balmer lines are formed deep in the interior, largely by collisional excitation. Heating within the clouds is provided by soft X-ray radiation, while Lymal alpha is formed mainly by recombination after photoionization. The ratio Lymal alpha/Halpha is expected to depend weakly on the ratio of ionizing ultraviolet luminosity to X-ray luminosity (L sub UV/l sub x). If the Lymal alpha luminosity is used as a measure of L sub UV' a weak dependence of Lymal/H alpha on the X-ray luminosity is found similar to previous results.

Kriss, G. R.↗
NASA NTRS1986

X-ray studies of Seyfert galaxies and quasars

Einstein X-ray observations of optically selected radio-quiet quasars are presented (summarizing the report of Kriss and Canizares, 1985) and analyzed along with published data. The data set comprises 77 quasars (including nine new high-red-shift quasars) and Seyferts and 101 upper limits. The ratio of X-ray to optical luminosity in the quasars is found to decrease as optical luminosity increases and to depend only weakly on red shift, and statistical discrepancies between the optically selected sample and the X-ray-selected Medium Sensitivity Survey (Gioia et al., 1984) are discussed. Also included are analyses of X-ray spectra and short-timescale variability for 64 Seyfert galaxies: variability is detected in IIIZw2, Mkn 766, and Mkn 78.

Canizares, Claude R.↗
NASA NTRS1999

Superwinds in Seyfert Galaxies SFGs and AGN

This project was successfully completed; three refereed publications have been published on the work and the graduate student involved successfully defended his thesis. The work done in conjunction with this project demonstrated for the first time the importance of large scale winds in most if not all Seyfert galaxies and explored the physical parameters of those winds and their effect on both the interstellar medium of the host galaxy and the activity in the active nucleus as well.

Baum, Stefi↗
NASA NTRS1984

Fluorescent excitation of Fe 2, Mn 2, Ti 2, N 1 lines by V 4, N 5, O 6: Emission lines in the spectra of symbiotic stars and Seyfert galaxies

Analysis of the published IUE and ground based high resolution spectra of symbiotic stars, particularly RR Tel, shows that the dominant excitation mechanism of Fe II, Mn II, Ti II, and N I lines is the selective fluorescent excitation of some levels by the strong C IV, N V, and O VI emission lines. The same mechanism should work for the excitation of Fe II lines in the spectra of Seyfert galaxies and Q60's whose emission spectra are quite similar to those of symbiotic stars. The similarities and differences between the fluroescent excitation mechanism reported herein and the Bowen's mechanism is analyzed.

Gilra, D. P.↗
NASA NTRS1978

A theoretical and observational analysis of He I triplet lines in class 1 Seyfert galaxy spectra

The equations of statistical equilibrium are solved for 11 levels of the helium atom that are most relevant to the production and radiative transfer of He I triplet lines. Solutions are obtained for several densities and temperatures over a run of optical depth in the 10,830-A line, and the results for emission-line strengths are plotted. Spectrophotometric scans and pertinent line strengths are presented for the class 1 Seyfert galaxies 3C 120, NGC 7469, and Mrk 618, as well as for Mrk 335, which exhibits a 'more normal' He I 5876/H-beta ratio. A comparison of the theoretically determined line intensities with the observational results verifies that the He I triplet line intensities are significantly enhanced by electron collisional excitation from 2(3)P and 2(3)S. It is suggested that the gas which gives rise to the broad He I lines in 3C 120, Mrk 618, and NGC 7469 is characterized by a number density of about 5 billion per cu cm, a temperature of approximately 15,000 K, and an optical depth of 100 to 120 in the 10,830-A line.

Feldman, F. R.↗
NASA NTRS1986

IUE absorption studies of broad- and narrow-line gas in Seyfert galaxies

The interstellar medium of a galaxy containing an active nucleus may be profoundly affected by the high energy (X-ray, EUV) continuum flux emanating from the central source. The energetic source may photoionize the interstellar medium out to several kiloparsecs, thereby creating a global H II region. The International Ultraviolet Explorer (IUE) satellite has attempted to observe in several Seyfert galaxies (NGC 3516, NGC 4151, NGC 1068, 3C 120) the narrow absorption lines expected from such global H II regions. Instead, in two of the galaxies (NGC 3516, NGC 4151) broad, variable absorption lines at C IV lambda 1550, N V lambda 1240, and Si IV lambda 1400 were found, as well as weaker absorption features at O I lambda 1302 and C II lambda 1335. These features swamp any possible global H II region absorption. Such broad absorption features have previously been observed in IUE data, but their origin is still not well understood.

Voit, G. M.↗
NASA NTRS1990

Evidence for a supermassive black hole in the nucleus of the Seyfert galaxy NGC 5548

The international campaign to monitor the variable Seyfert 1 galaxy NGC 5548 with the IUE has provided an extensive and well-sampled set of spectroscopic observations. These observations are used to study the response of the C IV 1550 A emission-line profile to changes in the photoionizing continuum. Near the end of the IUE campaign, the continuum flux at 1440 A and the total C IV flux dopped by factors of 2.9 and 1.8, respectively, in 16 days. The red wing of the C IV profile responded more rapidly to the sharp continuum drop than the blue wing, indicating that clouds in the inner broad-line region (BLR) are undergoing gravitational infall. These results provide direct evidence that the central engine is a supermassive object, presumably a black hole, with a mass on the order of 10 to the 7th solar masses. Analysis of the profile variations also demonstrates that excess emission in the blue wing of C IV is from a component that is physically distinct from the bulk of the BLR.

Crenshaw, D. Michael↗
NASA NTRS1999

On X-Ray Variability in Seyfert Galaxies

This paper presents a quantification of the X-ray variability amplitude for 79 ASCA observations of 36 Seyfert 1 galaxies. We find that consideration of sources with the narrowest permitted lines in the optical band introduces scatter into the established correlation between X-ray variability and nuclear luminosity. Consideration of the X-ray spectral index and variability properties together shows distinct groupings in parameter space for broad and narrow-line Seyfert 1 galaxies, confirming previous studies. A strong correlation is found between hard X-ray variability and FWHM Hbeta. A range of nuclear mass and accretion rate across the Seyfert population can explain the differences observed in X-ray and optical properties. An attractive alternative model, which does not depend on any systematic difference in central mass, is that the circumnuclear gas of NLSy1s is different to BLSy1s in temperature, optical depth, density or geometry.

Turner, T. J.↗
NASA NTRS1988

Compact radio cores in three Seyfert galaxies - High resolution studies of Mkn 3, Mkn 231, and Mkn 463

The small-scale morphologies of Mkn 231 and Mkn 463 have been investigated using the European VLBI Network (EVN) at 1.6 GHz and the VLA at 15 and 22 GHz. Mkn 3 has been studied using the EVN at 1.4 and 1.6 GHz. All of the galaxies have a substantial fraction of their core radio flux in linear or elongated structures, typically tens of parsecs in extent. Agreement between the parsec- and kiloparsec-scale position angles of continuum radio emission suggests collimated outflow from the galaxy centers that continues over several orders of magnitude in scale. Supernova rates of order one hundred per year on scales of tens of parsecs are required to explain the nuclear radio emission as the result of bursts of star formation. The luminosities, small extents, and linear morphologies of the radio sources all support the idea that the nuclear radio sources are energized by active galactic nuclei and therefore support the more general picture of Seyfert galaxy nuclei being low-luminosity quasars. All of the galaxies appear to have undergone violent interactions in the recent past.

Neff, S. G.↗