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  • 1
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    Second-epoch VLA observations of compact radio sources in NGC 253 (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Results are presented of second-epoch 6-cm VLA observations of the starburst galaxy NGC 253 in early 1989, approximately 18 months after the first observations identified more than 30 compact radio sources in the galaxy. The galaxy was also mapped at 3.6 cm. No new radio sources were found at 6 cm after the 18-month interval. Assuming that at least two-thirds of new type II supernovae would have been detectable radio emitters stronger than 3 mJy, the 95-percent confidence upper limit to the SN rate is 3.0/yr. None of the 13 sources with flux densities above 1 mJy showed significant decreases in strength over 18 months; the strongest source showed an apparent increase of 6.5 percent in flux density, which differs from that of Kronberg and Sramek (1985) for M82. The 3.6 map identified a number of new sources because of the reduction of confusion. The available spectral data show that a few of the resolved sources may be H II regions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 102; 875-881
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  • 2
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    Radio properties of type 1.8 and 1.9 Seyfert galaxies (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A number of type 1.8 and 1.9 Seyfert galaxies have been observed at the VLA in order to compare their properties with those of the other types of Seyfert galaxy. The observed types have radio luminosities in the range of 10 to the 39th-40.5th args/s, with the median near 10 to the 40th ergs/s. Most of these galaxies have radio sources with diameters of about 500 pc or less. The ratio of radio luminosity to featureless optical continuum luminosity in the Seyfert 1.8/12.9 galaxies and Seyfert 1.2/1.5 galaxies is intermediate between the values for Seyfert 1 and Seyfert 2 galaxies. The infrared-to-radio ratio decreases along the sequence from Seyfert 1 galaxies, through intermediate Seyfert galaxies, to Seyfert 2 galaxies. This systematic statistical difference in the ratio of two aspect-independent quantities implies that the differences among the Seyfert classes cannot be attributed solely to differences in viewing angle.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 310; 136-144
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  • 3
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    Radio properties of the highly polarized, quiescent quasar OI 287 (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The highly polarized, quiescent quasar OI 287 has been observed with high resolution at 2 cm and 6 cm in an effort to determine the origin of some of the object's peculiar properties. The results seem to rule out the classification of OI 287 as a blazar. Extrapolation of the radio core spectrum to midinfrared wavelengths fails to predict the infrared flux by at least an order of magnitude. This supports the conclusion that the infrared emission and the radio emission do not originate in the same synchrotron-emitting component. The high optical polarization could be related to possible broad absorption lines in the unobserved UV regime, or it could be caused by reflection into the line of sight by scattering agents distributed in a thin disk.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 328; 569-577
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  • 4
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    Radio structures of Seyfert galaxies. VII - Extension of a distance-limited sample (1989)
    In:  Other Sources
    Details
    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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  • 5
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    Do the compact radio sources in NGC 253 and M82 fade over time? (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The nearby starburst galaxy NGC 253 has been observed at a third epoch at 6 cm, and a second epoch at 3.6 cm, using the highest resolution configuration of the Very Large Array (VLA). Over a total time span of 4 yr between 1987 and 1991, no new compact radio sources have appeared. The flux density limit ranges from 3 mJy (3 times the power of Cas A) for most of the main body of the source to approximately 0.3 mJy off the diffuse source surrounding the nucleus. Furthermore, there is no evidence for significant source fading over 4 yr, in contrast to the result reported by Kronberg & Sramek (1985) for M82. More recent data suggest that, except for the strongest source in that galaxy, the compact radio sources in M82 may not be fading after all. If this suggestion proves correct, supernova rates of 0.2-0.3/yr in M82, estimated based on the assumed source fading, are incorrect. More accurate limits on source fading indicate that the current rate of production of radio supernovae in M82 is no greater than 0.1/yr, while that in NGC 253 is no greater than 0.25/yr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 424; 1; p. L29-L32
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  • 6
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    Radio structure in the inner 1 arcsecond of NGC 1068 (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: High-resolution VLA and VLBI observations of NGC 1068 at several different wavelengths are reported. These observations provide new information about the triple radio source in the central arcsec (75 pc) of the galaxy. The 21-cm European VLBI Network observations at 0.05-arcsec resolution detect a core of flux density 89 + or - 10 mJy. This core is dominated by a component less than 20 marcsec (1.5 pc) in diameter that has a brightness temperature of about 10 to the 8th K. Two more components may have been detected by the VLBI observations, one on either side of the compact core. At 0.07-arcsec resolution, the 1.3-cm VLA map of the central arcsec of NGC 1068 reveals a C-shaped radio morphology on scales from 10 to 50 pc. A comparison of the relative locations of the three components in the VLA and VLBI maps shows that the compact core in the VLBI map probably should be identified with the central component in the 1.3- and 2-cm VLA maps. If this identification is correct, the central component in the VLA maps is the actual nucleus of the galaxy. The core of the inner triple radio source may contain a significant flat-spectrum component. The presence of a compact core and the evidence for bending strengthen the argument that the inner triple radio source is produced by a mechanism similar to that operating in powerful radio galaxies. For a minimum-energy configuration, magnetic-field strengths of about 1 mG and energy densities of about 100 nerg/cu cm are found for the components of this source.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 93; 22-28
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  • 7
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    A radiative bow shock wave (?) driven by nuclear ejecta in a Seyfert galaxy (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: New VLA maps at 2 cm of the 13-arcsec-scale linear radio source in the center of NGC 1068 are described. The northeast lobe shows a limb-brightened conical morphology, very sharp 'leading' edges, and a magnetic field running parallel to these edges. The spectral index between 2 and 6 cm in these line-brightened regions is near 1.0. The northeast subpeak has a very steep radio spectrum between 18 and 2 cm which is attributed to inverse Compton losses of the relativistic electrons on the infrared photons. The spectral indices in the southwest lobe lie in the range 0.9-1.5 except in its northern parts, where a much larger index is found. The northeast lobe radio emission could arise in either the cocoon of old jet material which has passed through the internal shock in the ejecta and blown out to either side, or in interstellar material compressed by a bow shock wave driven into the galactic ISM.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 319; 105-117
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