Seyfert Nuclei Research Articles

The environment of seyfert galaxies

We made a nearest neighbour analysis on the cluster galaxies in the CfA sample. We found that galaxies with nearest distances below 20 kpc show a clear excess of Seyfert nuclei (i.e., the incidence of Seyferts among such galaxies is about 3 times higher than the average). This shows that the existence of nearby galaxies probably provides a favourable environment for generating Seyfert type activities.

PKS1345+125:a Seyfert nucleus merging with a powerful radio galaxy

The bright compact radio source PKS1345+125 (4C 12.50) has been optically identified with a magnitude 17 galaxy with a redshift z=0.122 (refs 1, 2) and an unusual spectrum3. Here we show it to be an elliptical galaxy with a compact radio source coincident with its optically undistinguished nucleus. An unresolved radio-quiet Seyfert nucleus with the same redshift as the elliptical galaxy is offset by 1.8 arc s from the radio source. The Seyfert nucleus is remarkable for its location in an elliptical galaxy, for its extreme far-infrared flux, and for the very low density in the broad-line region. We present a model of 1345+125 involving the dynamical merger of an elliptical galaxy with a spiral. The merger has stripped the spiral galaxy of its interstellar gas, fuelling the nuclear engines in both galaxies, and allowing the broad-line region to stream out freely. The elliptical has acquired an envelope, and is becoming a radio-loud cD galaxy.

THE GALACTIC CENTER : THE NEAREST SEYFERT NUCLEUS.

ABSTRACT Recent observations of the central 10 pc of the Galaxy are reviewed. The compact nonthermal radio source has a diameter of less than 20 AU, and an elongated source structure, which has been observed for the first time at a wavelength of 3.6 cm. It is a unique radio source in the Galaxy, but it is similar to the nuclear radio sources in external galaxies. Observations of the ionized gas in Sgr A West at a 0.3 arcsec resolution support an infall hypothesis for its origin in the central 3 pc. Similarities of the galactic center to Seyfert nuclei are pointed out.

A survey of neutral hydrogen absorption in the nuclei of active spiral galaxies

view Abstract Citations (49) References (77) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey of Neutral Hydrogen Absorption in the Nuclei of Active Spiral Galaxies Dickey, J. M. Abstract Nineteen spiral and irregular galaxies with bright continuum nuclei have been observed with the VLA to search for absorption at λ = 21 cm by cool atomic hydrogen in or in front of the nuclei. Most of these galaxies show activity at other wavelengths, such as Seyfert nuclei, intense far-IR emission, and X-ray emission. Fifteen absorption lines were detected, and six tentatively detected, in 15 of these galaxies. The line centers are offset from the systemic velocities by as much as 500 km s-1. Infall is more common than outflow at these high velocities, although the more common lines with offsets of less than 100 km s-1 are evenly distributed between infall and outflow. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163793 Bibcode: 1986ApJ...300..190D Keywords: Absorption Spectra; Active Galaxies; Galactic Nuclei; Hydrogen; Neutral Gases; Radio Astronomy; Spiral Galaxies; Centimeter Waves; Mass Distribution; Radio Sources (Astronomy); Seyfert Galaxies; Spectral Line Width; Astrophysics; GALAXIES: INTERNAL MOTIONS; GALAXIES: NUCLEI; RADIO SOURCES: 21 CM RADIATION full text sources ADS | data products SIMBAD (38) NED (35)

Variability in the optical continuum of Type 1 Seyfert nuclei

In 1979 we started a monitoring program of Seyfert galaxies, using various telescopes at ESO (La Silla, Chile). At present this program is still continuing, but here we discuss only the photometric data obtained in the period 1979–1982.

Galactic nuclei luminosity: A model of steady spherically-symmetric accretion of optically-thick gas on to Kerr black holes

Stationary spherically-symmetric accretion on to Kerr black holes is studied. A theoretical model has been developed in which the relativistic equations of continuity, conservation of four-momentum, local energy balance, and synchrotron radiative transfer have been integrated, by means of a combination of analytical and numerical procedures. A special emphasis has been put on evaluating the outcoming fluxes, as they can be compared with observations. Calculations were performed for masses of black holes in galactic nuclei, 106M⊙ as representative of the hypothetical black hole in the nucleus of the Milky Way and 107M⊙ as representative of a moderate Seyfert nucleus. The emergent spectra differ considerably from observations, as they are severely modified by dust in more external regions. The total frequency-integrated luminosity is, however, in very good agreement with observations.

Spectrophotometric investigation of NGC 4922

The results of a spectrophotometric investigation of the binary galaxy NGC 4922 are presented. One of the components is an elliptical galaxy with integrated absorption spectrum corresponding to the spectral classes GO-G3, while the second has the spectral features of a Seyfert nucleus with low degree of ionization. The physical conditions and chemical composition of the second component are also similar to those in a type 2 Seyfert galaxy. The mass of the Seyfert-like component within a radius of 1 kpc is found to be about 0.4.10/sup 8/M., and the mass of the complete system 2.2.10/sup 11/M.

Infrared observations of LINER galactic nuclei

view Abstract Citations (71) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared observations of liner galactic nuclei. Willner, S. P. ; Elvis, M. ; Fabbiano, G. ; Lawrence, A. ; Ward, M. J. Abstract Energy distributions from 1 to 20 microns are presented for a sample of galaxy nuclei all meeting the spectroscopic definition for LINERs (low-ionization nuclear emission-line regions). Shortward of 5 microns most of the nuclei show only stellar emission with normal colors, but at 10 and 20 microns, most nuclei show dust emission. The dust luminosities are correlated with the H-alpha luminosities and are consistent with the hypothesis that the same ultraviolet source ionizes the emission-line gas and heats the dust. The dust almost certainly does not compete strongly for ionizing photons. The ionizing source cannot have a spectrum consisting of a single power law extending from infrared to soft X-ray wavelengths. The observations thus strongly favor photoionization models in which the ionizing source is intrinsically weaker than in Seyfert nuclei. Publication: The Astrophysical Journal Pub Date: December 1985 DOI: 10.1086/163712 Bibcode: 1985ApJ...299..443W Keywords: Cosmic Dust; Galactic Nuclei; Infrared Astronomy; Luminosity; Seyfert Galaxies; Calibrating; Flux Density; Near Infrared Radiation; Photoionization; Astrophysics full text sources ADS | data products SIMBAD (46) NED (45)

Dual emission-line regions in the Seyfert galaxy NGC 5929

Several theoretical and empirical studies suggest that multiple distinct emission regions exist in the nuclei of some active galaxies. Detailed study1,2 of nearby objects such as M51 shows that the most important radiation of nonstellar origin can originate hun-dreds of parsecs from the nucleus (as defined by the stellar potential well), while binary compact objects are expected in some cluster-collapse schemes3 or in interaction-fuelled models for active nuclei4,5. Here I show that the type 2 Seyfert nucleus of NGC5929 contains two emission regions situated symmetrically about the centre of the galaxy. Slit spectroscopy shows them to be spatially as well as kinematically distinct, each with a linewidth of ∼200 km s−1 and ionization levels normally associated with Seyfert nuclei. Their location in the galaxy's rotation curve suggests that they move with the galaxy's disk gas; and they probably result from energy transport from a central object of low photon luminosity but high energy output. This system furnishes a very clear example of the presence of phenomena related to the presence of a central engine, but located at a significant distance from the ultimate source of energy. The existence of such objects suggests that the usual radiatively powered, nearly symmetric models for active nuclei may be misleading in many objects.

Recognition and classification of galaxies with optical jets

view Abstract Citations (38) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Recognition and classification of galaxies with optical jets. Keel, W. C. Abstract Deep images and spectra are presented for galaxies reported in various catalogs to have jets, as well as in a search of the SRC J survey plates in a region near the south galactic pole. Most of these are shown to be superpositions, polar rings, tidal features, or artifacts of the original plate material. Examples are shown of ten ways that false jets can be produced, with more detailed case studies for several systems. Based on this experience, several criteria for the brightness, location, and symmetry of genuine optical jets are suggested, which should yield survey samples much less contaminated by 'false alarms' than existing ones. Among the objects that remain as optical-jet candidates, ESO 0610-23 shows a linear, radial chain of H II regions on the outskirts of an amorphous system with complex internal structure, UGC 3995 is a close pair of spirals, one of which has a type 2 Seyfert nucleus and apparent knotty jet, and NGC 1598 has the radial features previously reported, but considerable chaotic outer structure as well. Several systems (such as AM 0207-49 and ESO 2330-38) illustrate the intrinsic difficulty of separating jets and tidal tails on morphological grounds alone in certain cases. Publication: The Astronomical Journal Pub Date: November 1985 DOI: 10.1086/113923 Bibcode: 1985AJ.....90.2207K Keywords: Classifications; Error Analysis; Galactic Structure; Plasma Jets; Spiral Galaxies; Visible Spectrum; Galactic Nuclei; H Ii Regions; Seyfert Galaxies; Astrophysics full text sources ADS | data products NED (68) SIMBAD (53)

Universal mass-luminosity relation for quasars and active galactic nuclei?

The masses of the central sources in quasars and active galaxies are determined, assuming the H..beta.. line velocity widths are gravitationally induced, and using the H..beta.. luminosities to estimate the distances of the broad-line regions (BLR) from the central sources. It is found that the continuum luminosities are proportional to the masses thus determined. The average ratio of the optical continuum luminosity to the Eddington luminosity is 0.01, with a scatter of less than a factor of 3, over four orders of magnitude in luminosity. In addition, it is shown that the ratio of X-ray to H..beta.. luminosity, which in this picture is proportional to the ionization parameter, is anticorrelated with the total luminosity. This supports previous findings that the ionization parameter in the BLR of Seyfert nuclei is higher than that of quasars.

The effects of interactions on spiral galaxies. I - Nuclear activity and star formation

We present results of spectrophotometry of the nuclei of 161 (mostly spiral) galaxies with bright companions, and emission-line imaging of 63 galaxies. The program includes a complete sample, unbiased as to morphological disturbance, and an Arp-atlas sample selected for visual evidence of tidal distortion. When compared to a similarly observed sample of isolated-spiral nuclei, both samples of interacting galaxies show significant excesses of nuclear emission. Both nonthermal (Seyfert) activity and nuclear star formation are enhanced, while low-ionization (LINER) nuclei are uncommon. The rate of nuclear star formation is significantly above average even in systems without noticeable tidal distortion in the outer disks, suggesting that the near-nuclear gas is only marginally stable in isolated galaxies. There is evidence that Seyfert nuclei are more frequent in very close pairs. Very disrupted systems possess significantly fewer Seyfert nuclei. These effects become more pronounced with increasing galaxy luminosity. Sizes of nuclear emission regions appear to be unchanged by interactions. The enhancement in nuclear star formation depends only weakly on pair separation over the range we have sampled. Our results suggest that nuclear phenomena are triggered by tidally induced influx of gas from the disk into the nuclear regions, rather than gas transfer between themore » galaxies.« less

The nuclear activity of interacting galaxies

view Abstract Citations (262) References (82) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nuclear Activity of Interacting Galaxies Dahari, O. Abstract A search for active galactic nuclei among interacting galaxies is reported. A sample of 167 systems of interacting and asymmetric galaxies was observed spectrophotometrically in the spectral range 4700-7100 A. The results are compared with a sample of isolated galaxies. It is found that (1) there are no Seyfert nuclei in elliptical or dwarf irregular galaxies of the sample; (2) there is an excess of Seyfert nuclei among interacting spirals, but it is only at the 90 percent confidence level; (3) this excess becomes statistically significant (98 percent) when only strongly interacting spirals are included (four new Seyfert nuclei are presented); (4) in the subgroup of galaxies with extreme tidal distortions, no Seyfert nuclei were found. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1985 DOI: 10.1086/191021 Bibcode: 1985ApJS...57..643D Keywords: Astronomical Photometry; Astronomical Spectroscopy; Galactic Clusters; Galactic Nuclei; Interacting Galaxies; Seyfert Galaxies; Active Galactic Nuclei; Astronomical Catalogs; Data Reduction; Gravitational Effects; Interactions; Spectrophotometry; Spiral Galaxies; Astrophysics full text sources ADS | data products NED (249) SIMBAD (235) Related Materials (1) Erratum: 1986ApJS...60..601D

Spectropolarimetry of Seyfert nuclei

The present optical spectropolarimetry of six strongly polarized type 1 and 2 Seyfert nuclei, with a spectral resolution of about 10 A and a typical coverage of 3300-7100 A, facilitates comparisons of polarization between various permitted and forbidden emission lines and the continuum. Additional broadband data extend the baseline to the atmospheric UV cutoff and to 8600 A for evaluation of the overall wavelength dependence. Among the galaxies studied, only NGC 6814 is entirely polarized by the Galaxy, which is in the foreground. No evidence requires an intrinsically polarized nonthermal source, although the results for Mrk 3 and NGC 3227 can be interpreted in terms of the dilution of a flat, strongly polarized continuum by starlight. 51 references.

Kinematics of the broad-line emission gas in quasars and Seyfert nuclei - Line profiles in a gravitational model

view Abstract Citations (29) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Kinematics of the broad-line emission gas in quasars and Seyfert nuclei - Line profiles in a gravitational model Carroll, T. J. ; Kwan, J. Abstract The parabolic-orbital model reported by Kwan and Carroll in 1982 for the broad emission-line regions of quasars and Seyfert galaxies is extended and improved to include the effects of a finite infalling cloud number and size. Disruption of the cloud by the differential angular momentum across its face results in a large velocity dispersion among the resulting fragment cloudlets. This velocity dispersion compensates for the small number of clouds at high velocity so that a fairly smooth profile is obtained. The drag of a confining intercloud wind is also considered. The major dynamical effect of this drag is to trap clouds with less than a certain angular momentum, l < 300 km s-1 x 50 pc for our standard model parameters. The trapping of clouds produces an asymmetry in the Lyα profile due to the absence of an outward leg for the trapped clouds. The asymmetry is reduced by the spiralling of the cloud material, and it shows up mainly in the core and far wings of the profile. The dependence of various line emissivities on the incident ionizing flux has been computed by Kwan in 1984. His results are convolved with the cloud velocity dispersions, and the resulting emission-line profiles demonstrate that the gravitational model can reproduce the observed broadness of He I λ5876 relative to Hβ (updated by Shuder in 1982). Profiles for Lyα, Mg II λ2798, C IV λ1549, and C III] λ1909 are also generated and compared to existing observations. Publication: The Astrophysical Journal Pub Date: January 1985 DOI: 10.1086/162765 Bibcode: 1985ApJ...288...73C Keywords: Astronomical Spectroscopy; Emission Spectra; Galactic Nuclei; Gravitational Effects; Kinematics; Quasars; Seyfert Galaxies; Astronomical Models; Clouds; Drag; Line Spectra; Astrophysics full text sources ADS |

IR observations of the peculiar galaxy Arp220

Observations from IRAS (the Infrared Astronomical Satellite) have shown that the peculiar galaxy Arp220 (=IC4553) has extreme IR properties1. Its IR luminosity is 100 times greater than normal spirals and nearly equals that of the most luminous Seyfert known, Mkn231. Its optical appearance suggests that it is either a recent merger or that it has a prominent central dust lane. Soifer et al.1 have discussed whether a starburst or a Seyfert nucleus can better explain their observations. We report here 20-, 350- and 760-µm observations which constrain the mass and size of the emitting region and compare Arp220 with the archetypal starburst galaxy M82.

Photoionization models and diagnosis of physical properties of the broad-line emission gas in quasars and Seyfert nuclei

view Abstract Citations (111) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoionization models and diagnosis of physical properties of the broad-line emission gas in quasars and Seyfert nuclei Kwan, J. Abstract The earlier photoionization calculations of Kwan and Krolik are extended and improved. The present models all pertain to slabs of finite column densities. The 0 Ι and Fe ΙΙ multilevel systems are modeled better, and the dependence of different line ratios on the physical conditions is illustrated graphically. It is found that O Ι λ1304/ 8446 and Fe ΙΙ λλ 2240-2250/λλ4450-4750 are good gauges of the cloud column density. The relative flux of several semiforbidden transitions, namely, N Ιv] λ1486, O Ιv] &lambda1402, and 0 ΙΙΙ] λ 1663, to that of C ΙΙΙ] λ1909 are useful density diagnostic ratios, in addition to C ΙΙΙ] λ1909/C Ιv λ1549. Lyβ/Lyα, Hβ/Hα, Lyα/O Ι λ1304, He Ι λ5876/Hβ, C Ιv λ1549/Mg ΙΙ λ2798, and Fe ΙΙ λλ2240-2650/ Mg ΙΙ λ2798 all depend strongly on the incident continuum flux. The quantitative dependence of all these ratios on the physical parameters will provide tests of the photoionization model, a framework for modeling an individual quasar spectrum, and, in conjunction with kinematic models, allow specific calculations of both the relative intensities and profiles for the different lines. Publication: The Astrophysical Journal Pub Date: August 1984 DOI: 10.1086/162275 Bibcode: 1984ApJ...283...70K Keywords: Astronomical Spectroscopy; Galactic Nuclei; Photoionization; Quasars; Seyfert Galaxies; Astronomical Models; Correlation; Emission Spectra; H Lines; Iron; Astrophysics full text sources ADS |

A luminous 3 kiloparsec infrared disk in NGC 1068

A 10 micron map of the Seyfert galaxy NGC 1068 and airborne measurements of its angular extent in the far-infrared are presented. It is shown that the infrared emission originates primarily from two physically distinct regions; approximately half of the total infrared luminosity of 3 x 10 to the 11th solar luminosities is associated with the Seyfert nucleus and half with a 3 kpc (35 arc sec) diameter disk surrounding it. It is argued that the disk component of infrared emission originates from an extended but heavily obscured burst of star formation which resembles those seen in some non-Seyfert galaxies. This high-luminosity disk is distinguished more by its large size than by its high surface brightness. On the basis of current evidence it cannot be concluded that the high disk luminosity in NGC 1068 is causally related to its Seyfert activity.

JHKL PHOTOMETRY OF THE NUCLEI OF NORMAL SPIRAL GALAXIES.

ABSTRACT Photometry with a small beam size is presented of the nuclei of five spiral galaxies selected for the absence of nuclear activity. No infrared excesses are found, and the color indices of all five galaxies are the same within the uncertainties. The emission of this sample can be explained in terms of a late-type stellar population. These results contrast with earlier results both for Seyfert nuclei and some supposedly normal spiral nuclei, which showed 3.5-μm excesses.

A Survey of Southern Compact and Bright Nucleus Galaxies

During the 1960's, Zwicky made an intensive examination of the Palomar Sky Survey plates that resulted in his “Catalogue of Galaxies and of Clusters of Galaxies” (Zwicky et al. , 1961-1968). In the course of this study, he picked up numerous examples of what he labelled as “compact galaxies and compact parts of galaxies”; five lists were initially circulated and later presented as a catalogue (Zwicky 1971). To Zwicky the “compact” connotation suggested extremely high stellar densities, but line profiles failed to reveal the large velocity distributions expected of such concentrations of stars. Nevertheless an unexpected benefit was that many of his “compact parts” turned out to be the nuclei of actives galaxies, particularly Seyfert galaxies. Furthermore, since the nuclei have to stand out to gain “compact part” status, Seyfert nuclei from Zwicky’s lists tend to be fairly extreme specimens.