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  • ASTROPHYSICS  (16)
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  • 1
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    The ionization cone, obscured nucleus, and gaseous outflow in NGC 3281 - A prototypical Seyfert 2 galaxy? (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Narrow-band images and long-slit spectroscopy of the central region of the highly inclined Seyfert galaxy NGC 3281 are presented. The image of the continuum-subtracted forbidden 4959 emission line shows a very clear conical morphology for the high-excitation gas. A possible similar structure can also be seen on the other side of the nucleus, but is dimmed by patchy obscuration in the dusk. The continuum images and long-slit spectroscopy are used to derive and map the extinction in the inner regions of NGC 3281; heavy obscuration is found along the present line of sight to the apex of the cone, suggesting that the true nucleus is located at the apex and is obscured. Low-resolution long-slit spectra are used to study the stellar population, which is found to be old, uniform within 2.5 kpc of the nucleus, and typical of the bulges of early-type galaxies. It is suggested that NGC3281 may be another example of a 'hidden' Seyfert 1, even though there is no direct evidence for a broad-line region in this particular galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 396; 1 Se; 45-61
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  • 2
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    Infrared spectroscopy of a Cygnus A - Implications for the obscured active nucleus (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Near-infrared spectroscopic observations of the central regions of the luminous radio galaxy Cygnus A are presented and interpreted in terms of an obscured quasar nucleus. Strong emission is detected in the molecular hydrogen lines 1-0 S(1) and 1-0 S(3), the strengths of which are accounted for through heating by the nuclear hard X-ray source. The large equivalent widths of these molecular hydrogen lines and the near-infrared narrow hydrogen recombination lines suggest that the observed nuclear continuum is strongly attenuated at 2 microns. The observed upper limit to the flux of broad Pa-alpha implies an extinction to the putative broad line region AV(BL) of at least 24 mag, and the observed continuum intensity of the nuclear point source at 2.2 microns gives an extinction of 43 +/-9 mag toward the optical-infrared continuum. These estimates are consistent with the gas column density inferred from the low-energy X-ray cutoff. Strong forbidden Si VI 1.962-micron line emission from Cygnus A is also reported.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 115-120
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  • 3
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    Radio structures of Seyfert galaxies. VII - Extension of a distance-limited sample (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The VLA has been used at 6 and 20 cm to observe 27 Seyfert galaxies with recessional velocities less than 4600 km/s that had not been mapped previously. The sample shows weak trends for Seyfert 2 galaxies to have more luminous and larger radio sources than Seyfert 1 galaxies. A 20 cm radio luminosity function is constructed for each Seyfert type and shown to be fairly flat for powers betwen 10 to the 20th and 10 to the 23rd W/Hz. About 10 percent of the galaxies in the present sample may have flat-spectrum components contributing a substantial amount of their total flux density at centimeter wavelengths.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 343; 659-671
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  • 4
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    High-resolution emission-line imaging of Seyfert galaxies. I - Observations. II - Evidence for anisotropic ionizing radiation (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A CCD direct imaging survey of 11 Seyfert galaxies with a mean seeing of 1.3 arcsec FWHM is presented. It is found that the major axes and spatial scales of the circumnuclear emission-line gas are very similar to those of the radio continuum sources. In the second part, this close connection between thermal and relativistic gases is examined. A scenario is proposed in which the radio jets and plasmoids shock, accelerate, and compress ambient and entrained gas, with the dominant source of ionization being the nonstellar nuclear UV continuum.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 334; 104-116
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  • 5
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    The radio source and bipolar nebulosity in the Seyfert galaxy NGC 3516 (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Results of radio continuum and optical emission-line observations of the type 1 Seyfert galaxy NGC 3516 are presented. The radio maps reveal an elongated one-sided curved structure, which comprises a series of small-scale 'blobs' and extends up to 4 kpc from the nucleus. This radio structure is aligned and cospatial with one side of the double-sided and highly symmetric Z-shaped emission-line structure. It is argued that these morphological features are associated with a bipolar gaseous outflow from the nucleus of NGC 3516. The radio 'blobs' are elongated roughly perpendicular to the apparent local direction of the outflow, a result which is interpreted in terms of synchrotron emission from outflow-driven shock waves.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 385; 137-145
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  • 6
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    Soft X-ray spectra of Seyfert 2 galaxies (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The paper presents soft X-ray spectra of three Seyfert 2 galaxies obtained with the ROSAT PSPC. For two of these objects, NGC 5506 and MCG -5-23-16, most of the flux occurs at energies greater than 1 keV and probably represents a low-energy extension of the source seen at higher (greater than 2 keV) energies. The third source, Mrk 348, has very little flux in the ROSAT band, suggesting a photoelectric cutoff at energies above the ROSAT band, in agreement with Ginga observations. In all three galaxies, X-rays are detected at energies below these photoelectric cutoffs with flux above that expected from a model in which the source has the same spectral index as at higher energies (2-10 keV) and is covered by a uniform, cold, photoelectric absorber. This result indicates the presence of an additional component at soft energies, which is referred to as a 'soft excess'. The monochromatic flux of the soft excess measured at 1 keV is about 1-2 percent of the directly viewed hard X-ray continuum in all three galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 1; p. 144-153.
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  • 7
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    Infrared emission in Seyfert 2 galaxies - Reprocessed radiation from a dusty torus? (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: New and existing data for a sample of nine Seyfert 2 galaxies with known 'ionization cones' are combined in order to test whether collimation results from shadowing of radiation from a small isotropic nuclear source by a thick dusty torus. The number of ionizing photons emitted by the compact nucleus is calculated from the emission-line ratios measured for gas within the cones. On the assumption that this compact nuclear source radiates isotropically, the optical-UV power incident on the torus, which is expected to be reradiated in the IR, is determined. It is found that the observed IRAS luminosities are consistent with the torus model in eight of the nine objects with sufficient data to perform the calculation. It is concluded that the data are generally consistent with collimation and reradiation by a dusty torus.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 395; 2 Au; L73-L77
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  • 8
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    The kinematics of the extended gas in the Seyfert galaxy NGC 3516 (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Long-slit spectroscopy of the extended gas in the Seyfert galaxy NGC 3516 reveals considerable substructure in the narrow emission lines with several kinematically distinct components visible in H-alpha and N II lambda 6583. The velocity measurements cover almost all of the 3 kpc scale, Z-shaped emission-line structure seen in narrow-band images and suggest that a significant rotational component is present. At large radii, strong deviations from this rotation are observed, indicating that a radial component of motion to the gas is also required to adequately describe the velocity field. There is a clear antisymmetry in these deviations with the velocities being blueshifted with respect to 'normal' galactic rotation on the southwest side of the nucleus and redshifted with respect to it on the northeast side. Although several models can be invoked to explain the observed velocities, the symmetries in the kinematics and emission-line morphology are most easily explained by a bent bipolar mass outflow from the nucleus. In this simple model, gas is ejected out of the plane of the stellar disk and is then slowed by gravitational forces. As the gas trajectory begins to bend, significant velocity deviations are produced. These observations provide some of the best kinematic evidence for mass outflow, although indirect arguments suggest they may be a common feature in many Seyfert galaxies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 394; 1 Ju
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  • 9
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    Double-peaked broad line emission from the LINER nucleus of NGC 1097 (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We report the recent appearance of a very broad component in the H-alpha and H-beta emission lines of the weakly active nucleus of the Sersic-Pastoriza galaxy NGC 1097. The FWZI of the broad component is about 21,000 km/s, and its profile is double-peaked; the presence of a blue, featureless continuum in the nucleus is also suggested. The broad component was first observed in H-alpha in November 2, 1991, and confirmed 11 months later. The H-alpha profile and flux did not change in this time interval. Comparison with previously published spectral data indicates that the broad lines have only recently appeared. Together with the relatively high X-ray luminosity and the compact nuclear radio source, our results characterize the presence of a Seyfert 1 nucleus in a galaxy which had previously shown only LINER characteristics. Obscuring material along our line of sight to the nucleus appears to have recently cleared, permitting a direct view of the active nucleus. We discuss two possible structures for the broad line region, biconical outflow and an accretion disk, that could give rise to the observed profile.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 410; 1; p. L11-L14.
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  • 10
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    The radio emission of Seyfert galaxies (1991)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper reviews developments over the last decade in our understanding of the radio emission of Seyfert galaxies. After summarizing the characteristics and selection criteria of radio surveys. Properties of the integrated radio emission - radio luminosity functions, correlations of radio power with other properties, and spectra, are described. Radio structures are then discussed with emphasis on the different kinds of morphologies seen. Linear radio sources are morphologically and kinematically closely associated with the narrow line regions, and models attempting to account for this association are described. Diffuse radio sources are fuelled by circumnuclear star formation. The review concludes with some remarks on the implications of radio properties for unified models of type 1 and type 2 Seyferts.
    Keywords: ASTROPHYSICS
    Type: Workshop on the Interpretation of Modern Synthesis Observations of Spiral Galaxies; Mar 12, 1990 - Mar 15, 1990; Albuquerque, NM; United States
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