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Owen, F. N.

Publications and source records attributed to Owen, F. N..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The Northern Middle Lobe of Centaurus A: Circumgalactic Gas in a Starburst Wind

We present deep ultraviolet (GALEX), radio continuum (VLA) and H-alpha (Magellan) images of the circumgalactic medium around Centaurus A (NGC5128). We focus on the Northern Middle Lobe (NML), a region extending more than 50kpc beyond the galaxy and known to host a collection of striking phenomena: emission line filaments, recent star formation, disrupted HI/molecular gas streams, and short-lived X-ray clouds. Far UV emission is tightly correlated with H-alpha emission for more than 50kpc, and loosely associated with a filament of X-ray clouds and with the radio continuum emission. The radio emission in the NML region does not appear to be an extension of the inner radio jet (10kpc) or a typical radio lobe. We speculate that the "weather" seen in the NML region is a short-lived phenomenon, caused by an outflow encountering cool gas deposited by one of the recent merger/encounter events which have characterized the history of NGC5128.

Neff, S. G.↗
NASA NTRS1994

Radio continuum polarimetric imaging of high redshift radio galaxies

Multifrequency images of total and polarized radio continuum emission from the two high redshift radio galaxies 0902+343 (z = 3.40) and 0647+415 (4C 41.17, z = 3.80) are presented. These images represent the most sensitive polarimetric study of high redshift ratio galaxies to date. The emission from both galaxies is substantially polarized, up to 30% in some regions, and both sources sit behind deep 'Faraday screens,' producing large rotation measures, over 10(exp 3) rad/sq. m in magnitude, and large rotation measure gradients across the sources. Such large rotation measures provide further evidence that high redshift radio galaxies are situated in very dense environments. Drawing the analogy to a class of low redshift powerful radio galaxies with similarly large rotation measures, we suggest that 0902+343 and 0647+415 are situated at the centers of dense, x-ray 'colling flow' clusters, and that the cluster gas is substantially magnetized. The remarkable similarity between the optical and radio morphologies of 0647+415 on scales as small as 0.1 sec is presented. We consider, and reject, both synchrotron and inverse Compton radiation as possible sources of the optical emission. We also consider both scattering of light out of a 'cone' of radiation from an obscured nucleus, and jet-induced star formation, and find that both models encounter difficulties in explaining this remarkably close radio-optical alignment. High resolution spectral index images reveal compact, flat spectrum components in both sources. We suggest that these components are the active nuclei of the galaxies. Lastly, high resolution images of 0902+343 show that the southernmost component forms a 'ring' of 0.2 sec radius. We discuss the possibility that this ring is the result of gravitational lensing, along the lines proposed by Kochanek & Lawrence (1990).

Carilli, C. L.↗
NASA NTRS1984

What bends 3C 465?

This paper studies the interaction of the prototypical wide-angle tailed radio source 3C 465 with the ambient cluster gas. 3C 465 is attached to the dominant D galaxy NGC 7720 in the cluster Abell 2634. New VLA maps of the radio source are presented which reveal an inner jet and a rapid change of structure at the hot spots at the beginning of each tail. New X-ray maps of the cluster gas are also presented. It is shown that the sharp bend of the flowing radio-luminous plasma between the inner jets and the beginning of the tails cannot be explained by any of the conventional models. Neither galactic motion, buoyancy, gravitational bending, nor dynamic pressure can account for the bending of this source. Attention is also given to new possibilities for the dynamics of this type of radio tailed source: the effect of a current in the jets, and the interaction with cooling clouds in the cluster gas.

Eilek, J. A.↗
NASA NTRS1982

VLBI observations of the nucleus and jet of M87

The nucleus and jet of M87 was mapped with an eight-station very long baseline interferometric array at 18 cm wavelength with high dynamic range. It was found that the nucleus of M87 consists of a core-jet structure with a peak brightness temperature greater than 10 to the 10th K. Emission is shown to extend for more than 50 milli-arcsec with a brightness temperature exceeding 10 to the 8th K along a position angle of 288 degrees, which precisely matches the position angle of the 20'' radio/optical/X-ray jet. In addition, the nucleus contains a significant structure of lower brightness at approximately the same position angle, although no counterjet is observed. By invoking relativistic beaming in order to enhance the jet and diminish the counterjet, it is shown that the jet must be aligned within about 60 degrees to our line of sight, and its flow velocity must exceed about 60% of the speed of light. The knots embedded in the 20'' jet contain no bright compact structures, and the sizes of the innermost knot (knot D) is between 0.1-0.3''.

Reid, M. J.↗
NASA NTRS1982

A 1400-MHz survey of 1478 Abell clusters of galaxies

Observations of 1478 Abell clusters of galaxies with the NRAO 91-m telescope at 1400 MHz are reported. The measured beam shape was deconvolved from the measured source Gaussian fits in order to estimate the source size and position angle. All detected sources within 0.5 corrected Abell cluster radii are listed, including the cluster number, richness class, distance class, magnitude of the tenth brightest galaxy, redshift estimate, corrected cluster radius in arcmin, right ascension and error, declination and error, total flux density and error, and angular structure for each source.

Owen, F. N.↗
NASA NTRS1982

Near-infrared photometry of distant radio galaxies - Spectral flux distributions and redshift estimates

Calculations modeling the effects of stellar evolution on the observed colors of elliptical galaxies suggest that the shape of their spectra should remain almost constant in the red and near-infrared for red shifts greater than two. In order to test this idea, JHK photometry of optically faint radio source identifications believed to be faint elliptical galaxies were carried out. Photometric redshift estimates have been made using three different models: a nonevolving elliptical galaxy spectrum, an evolving spectrum based on one of Bruzual's calculations, and an empirical model derived from photometry of distant elliptical galaxies. Redshifts greater than 0.5 are systematically under-estimated by the first two models and for galaxies whose colors are not consistent with the models, deviations occur not only in the optical bands but also in the infrared. The difficulties are not resolved by the addition of a quasar-like nucleus to the galaxies.

Puschell, J. J.↗
NASA NTRS1982

VLBI observations of M87

Results of VLBI observations of the nucleus and jet of M87 at 1666.6 MHz in right circular polarization are presented. A hybrid map of the nucleus was made revealing the presence of a one-sided jet, whose position angle is 290.5 (+ or - 1) deg. Assuming that no counter-jet exists because of the effects of relativistic beaming, limits can be placed on the flow velocity of the jet, and the resulting ratio of the observed intensities of the jet to the counter-jet explains the absence of the counter-jet. Another explanation is that jets are intrinsically one-sided, or that counter-jet observed emissions are delayed. Finally, the possibility of existing small wiggles is considered, but further observations are required to verify their existence in M87.

Reid, M. J.↗
NASA NTRS1981

The correlation of X-ray emission with strong millimeter activity in extragalactic sources

A sample of 25 strong extragalactic millimeter sources have been observed at about 1 keV with the Imaging Proportional Counter on the Einstein X-Ray Observatory and at 90 GHz with the NRAO 11 m telescope. A strong correlation between the millimeter and X-ray flux densities is found. This result is consistent with a synchronous self-Compton model in which the X-ray emission arises from the Compton scattering of millimeter radio photons off the relativistic electrons which created them.

Owen, F. N.↗
NASA NTRS1981

The broad-band spectra and variability of compact nonthermal sources

It is noted that in approximately a dozen sources, nearly simultaneous infrared and/or visual spectra are available, making it possible to examine the relationship between the infrared-visual and radio regimes. A simple transition to the steeper infrared spectra is seen as likely with a mean break wavelength of approximately 300 microns in the rest frame. These observations indicate a tapered source geometry, with the smallest structures roughly on the order of 10 to the 16th cm as estimated from the spectral break; this is consistent with scales estimated from optical variability time scales. Large amplitude variations on a six-month time interval are found to be fairly infrequent in most of the sources. A relatively model-independent way of categorizing flux variations as due to changes in source scale, or structure or the slope of the electron energy spectrum is suggested.

Jones, T. W.↗
NASA NTRS1980

The very flat radio spectrum of 0735 plus 178 - A cosmic conspiracy

Multifrequency interferometric and total flux density measurements of the radiation from 0735 plus 178 are discussed. It is shown that it is far more likely that the very flat radio spectrum of this source results from a superposition of incoherent synchrotron radiation from four distinct, homogeneous components, each with a peaked spectrum, than from radiation from a single inhomogeneous component.

Cotton, W. D.↗
NASA NTRS1978

X-ray and radio emission from the compact galaxy III Zw 2

X-rays from the compact galaxy III Zw 2 have been detected with the rotating modulation collimator on board SAS 3. The (2-10-keV) flux is (4.3 + or - 0.5) by 10 to the -11th power erg/sq cm per sec, which corresponds to a luminosity of 1.4 by 10 to the 45th power erg/s at 530 Mpc. Subsequent radio observations between 1.46 and 90 GHz were made at the NRAO Very Large Array and 36-foot (11-m) installations. The radio spectrum rises sharply toward higher frequencies and, below about 100 GHz, is indicative of a self-absorbed synchrotron spectrum from an extremely compact, rapidly evolving object.

Schnopper, H. W.↗
NASA NTRS1977

Extragalactic sources with strong millimeter-wave emission

Observations at 90 GHz of a sample of 38 sources chosen to have flat or rising spectra between 0.318 and 5 GHz are reported. Roughly 25% of the sources were found to have flat or rising spectra between 5 and 90 GHz. The optical magnitude of each of the sources from the E print of the Palomar Sky Survey has also been estimated. Evidence is found for a correlation between the 90-GHz flux density and the optical magnitude, suggesting a relationship between the emission processes at these frequencies. Little evidence is found for a correlation between the low- and high-frequency spectral indices of the sources. This suggests that the sources tend to be opaque at centimeter wavelengths and optically thin at millimeter wavelengths. The properties of two of the more interesting sources are also discussed. Evidence is presented that strong millimeter activity may be generally associated with the BL Lac phenomenon.

Owen, F. N.↗