Identification of the Radio Sources in Cassiopeia, Cygnus a, and Puppis a.

Baade, W.; Minkowski, R.

doi:10.1086/145812

Cited by 296 publications

(116 citation statements)

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“…Within the probable-error limits, the right ascension of the centre of Cygnus-A coincides with that of the optical object with which the source was identified by Baade and Minkowski (1954). The present measurement thus provides further confirmation of an already well-established identification.…”

Section: (G) Virgo-asupporting

confidence: 82%

Fan-beam Observations of Radio Sources at 21 cm Wavelength

Labrum¹,

Krishnan²,

Payten³

et al. 1964

Aust. J. Phys.

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SummaryThe compound interferometer at Fleurs, N.S.W., has been used in observations of eight of the strongest radio sources, with a fan beam 1'· 53 wide at a wavelength of 21· 1 cm. Each of the sources was scanned from west to east; the brightness distributions in this direction have been observed, and the positions of the sources in right ascension have been determined with high absolute accuracy (probable error less than 1 s of time).The results confirm that Centaurus.A, Cygnus.A, and the Omega nebula are all closely·spaced double sources. Sagittarius-A, Taurus-A, Hydra-A, the Orion nebula, and Virgo-A have no ~e structure detectable with this angular resolution.Sagittarius-A is found to be some 8 8 away from the position given by earlier low resolution observations. In the case of Virgo-A, there is some indication that the radio source is centred in the "jet" rather than in the galaxy. For the other sources, previous identifications are confirmed; the measured right ascensions coincide with the optical objects within the probable-error limits.

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Section: (G) Virgo-asupporting

confidence: 82%

Fan-beam Observations of Radio Sources at 21 cm Wavelength

Labrum¹,

Krishnan²,

Payten³

et al. 1964

Aust. J. Phys.

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“…Suggested explanations have included (1) the merger of two galaxies (Baade & Minkowski 1954), (2) the intersection of a single galaxy by a dust lane (Osterbrock 1983), or (3) a bipolar scattering nebula (see, e.g., Stockton et al 1994). The presently favored model is that at least some of the central optical morphology results from scattering of light from a hidden nucleus located at the radio core.…”

Section: Introductionmentioning

confidence: 99%

AChandraX‐Ray Study of Cygnus A. II. The Nucleus

Young¹,

Wilson²,

Terashima³

et al. 2002

ApJ

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We report Chandra Advanced CCD Imaging Spectrometer and quasi-simultaneous Rossi X-Ray T iming Explorer (RXT E) observations of the nearby, powerful radio galaxy Cygnus A, with the present paper focusing on the properties of the active nucleus. In the Chandra observation, the hard ([a few keV) X-ray emission is spatially unresolved with a size (1.5 kpc, km s~1 Mpc~1) and coin-[1A H 0 \ 50 cides with the radio and near-infrared nuclei. In contrast, the soft (\2 keV) emission exhibits a bipolar nebulosity that aligns with the optical bipolar continuum and emission-line structures and approximately with the radio jet. In particular, the soft X-ray emission corresponds very well with the [O III] j5007 and Ha ] [N II] jj6548, 6583 nebulosity imaged with Hubble Space T elescope. At the location of the nucleus, there is only weak soft X-ray emission, an e †ect that may be intrinsic or result from a dust lane that crosses the nucleus perpendicular to the source axis. The spectra of the various X-ray components have been obtained by simultaneous Ðts to the six detectors. The compact nucleus is detected to 100 keV and is well described by a heavily absorbed power-law spectrum with (similar to other ! h \ 1.52~0 .12 0.12 narrow-line radio galaxies) and equivalent hydrogen column cm~2. This N H (nuc) \ 2.0~0 .2 0.1 ] 1023 column is compatible with the dust obscuration to the near-infrared source for a normal gas-to-dust ratio. The soft (\2 keV) emission from the nucleus may be described by a power-law spectrum with the same index (i.e., although direct Ðts suggest a slightly larger value for Narrow emission lines ! l \ ! h ), ! l . from highly ionized neon and silicon, as well as a "" neutral ÏÏ Fe Ka line, are detected in the nucleus and its vicinity kpc). The equivalent width (EW) of the Fe Ka line eV) is in good agreement (r [ 2 (182~5 4 40 with theoretical predictions for the EW versus relationship in various geometries. An Fe K edge N H (nuc) is also seen. The RXT E observations indicate a temperature of keV for the cluster gas kT \ 6.9~1 .0 0.3 (discussed in Paper III of this series) and cluster emission lines of Fe Ka and Fe Kb and/or Ni Ka.We consider the possibility that the extended soft X-ray emission is electron-scattered nuclear radiation. Given that 1% of the unabsorbed 2È10 keV nuclear radiation would have to be scattered, the necessary gas column cm~2] would absorb the X-rays rather than scatter [N H (scattering)^3.5 ] 1022 them if the gas is cold. Thus, the scattering plasma must be highly ionized. If this ionization is achieved through photoionization by the nucleus, the ionization parameter m [ 1 ergs cm s~1 and the electron density cm~3 given the observed distance of the soft X-ray emission from the nucleus. The elecn e^6 tron column density inferred from the X-ray observations is much too low to account for the extended optical scattered light, strongly suggesting that the polarized optical light is scattered by dust. The presence of highly ionized Ne lines in the soft X-ray spectrum requires 20...

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“…We note that the galaxy spectra indicate a low ionization level, as shown by the low ratio of C m]/C II] which varies from about 5 to 0.8 in our galaxy spectra; in QSOs the ratio is typically 20 (Davidson 1977;Baldwin and Netzer 1978) and is also very large in the composite UV spectrum of a Seyfert 1 galaxy described by Verón-Cetty, Verón, and Tarenghi (1983) and in the two narrow-lined AGN observed in the UV by Durret and Bergeron (1984). Clearly the mean state of ionization in the most distant radio galaxies is lower than in Sy 1 and Sy 2 nuclei and almost all QSOs.…”

Section: Some Unusual Physical Conditions In Powerful Radio Galamentioning

confidence: 50%

“…Perhaps they can be detected and identified back close to the epoch of galaxy formation, although this last statement is still more of an optimists's hope than a proven fact, of course. As Longair and Lilly recall, the early phase of effective utilization of radio galaxies as probes seen at great distance was initiated by Baade and Minkowski (1954) with Cygnus A at a redshift of % -0.06. This optically faint but radio-powerful galaxy has been a prototype of the most luminous of radio galaxies for 30 years.…”

Section: Contrasting Modern and Historical Studies Of Radio Galaxiesmentioning

confidence: 99%

Faint galaxies and cosmology

Spinrad

1986

PASP

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This paper reviews progress in two areas of optical research on faint galaxies. First I discuss the philosophy and techniques needed to employ radio galaxies as evolutionary and cosmological probes out to redshifts now approaching 2.0. Faint-galaxy spectroscopy is much aided by the presence of emission lines in the spectra; the 3CR galaxies atz > 0.5 are cooperative in this respect, and we discuss their enormous [On] and La emission lines in some detail. The distant radio galaxies seem to be systematically more active than their nearby counterparts.Radio galaxies can also be studied as galaxies of evolving stars; the present interpretations of visual and IR galaxy colors and magnitudes suggest modest lingering star formation over the past 10 10 years in many luminous radio galaxies.I conclude with a discussion on the location and utilization of faint radio-quiet red galaxies; these are giant E systems atz > 0.5. The study of these galaxies should constrain the epoch of large galaxy formation, if the collapse phase is roughly coincident in time with the galaxy's last major epoch of star formation.

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Identification of the Radio Sources in Cassiopeia, Cygnus a, and Puppis a.

Cited by 296 publications

References 0 publications

Fan-beam Observations of Radio Sources at 21 cm Wavelength

Fan-beam Observations of Radio Sources at 21 cm Wavelength

AChandraX‐Ray Study of Cygnus A. II. The Nucleus

Faint galaxies and cosmology

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