On the Indentification of Radio Sources.

Baade, W.; Minkowski, R.

doi:10.1086/145813

Cited by 204 publications

(125 citation statements)

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“…This distance for Cygnus is consistent with the optical identification of the source with colliding galaxies at 34 megaparsecs. The Cassiopeia result is at variance with the distance of 500 parsecs derived by Baade and Minkowski [5] for a supernova remnant in this direction. On the above interpretation of the radio results the nearest that this source could be placed is at 2-5 kiloparsecs, on the inner side of the second arm.…”

Section: -The Position Of the Gygnus And Cassiopeia Sources Relativesupporting

confidence: 59%

12. The measurement of the distance of the radio sources

Davies¹,

Williams²

1957

Symp. - Int. Astron. Union

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In radio astronomy it is becoming increasingly important to know the distance of the radio sources. An identification with astronomical objects observed optically is then more readily obtained and this in turn may allow further investigation of the mechanism of radio emission. A measurement of the distance of sources will also resolve the problem of their distribution in space, showing which are galactic and which are extra-galactic. Furthermore the surface area and absolute luminosity can be estimated from a knowledge of the distance and angular size of a source.

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Section: -The Position Of the Gygnus And Cassiopeia Sources Relativesupporting

confidence: 59%

12. The measurement of the distance of the radio sources

Davies¹,

Williams²

1957

Symp. - Int. Astron. Union

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“…7a and 7c is also suspicious. However this object exhibits such unusual properties that it has been interpreted either as a system of colliding galaxies (Baade & Minkowski 1954;Minkowski 1957;Rubin et al 1977;Hu et al 1983;Holtzman et al 1992), two superposed galaxies without interaction (De Young, Roberts & Saslaw 1973), or even an exploding galaxy (Burbidge, Burbidge & Sandage 1963;Burbidge & Burbidge 1965). Thus, it is likely that the morphology displayed by this galaxy is more complicated than that naively expected from the cooling flow phenomenon.…”

Section: Summary: Towards a Complete Picture?mentioning

confidence: 99%

Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows

Cardiel

Gorgas

Aragón-Salamanca

1998

Monthly Notices of the Royal Astronomical Society

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We have obtained radial gradients in the spectral features λ4000-Å break (D 4000 ) and Mg 2 for a sample of 11 central cluster galaxies (CCGs): 8 in clusters with cooling flows and 3 in clusters without. After careful removal of the emission lines found within the D 4000 and the Mg 2 bandpasses for some objects, the new data strongly confirm the correlations between line-strength indices and the cooling flow phenomenon found in our earlier study (Cardiel, Gorgas & Aragón-Salamanca 1995). We find that such correlations depend on the presence and characteristics of emission lines in the inner regions of the CCGs. The nuclear indices are correlated with the mass deposition rate (Ṁ ) only when emission lines are found in the central regions of the galaxies. The central D 4000 and Mg 2 indices in cooling flow galaxies without emission lines are completely consistent with the indices measured in CCGs in clusters without cooling flows. CCGs in cooling flow clusters exhibit a clear sequence in the D 4000 -Mg 2 plane, with a neat segregation depending on emission-line types (Heckman et al. 1989) and blue morphology (McNamara 1997). This sequence can be modelled, using stellar population models with a normal IMF, by a recent (∼ 0.1 Gyr old) burst of star formation, although model uncertainties do not allow us to completely discard a continuous star formation or a series of bursts over the last few Gyr. In CCGs with emission lines, the gradients in the spectral indices are flat or positive inside the emission-line regions, suggesting the presence of young stars. Outside the emission-line regions, and in cooling flow galaxies without emission lines, gradients are negative and consistent with those measured in CCGs in clusters without cooling flows and giant elliptical galaxies. Index gradients measured exclusively in the emission-line region correlate withṀ . Using the same population models we have estimated the radial profiles of the mass transformed into new stars. The derived profiles are remarkably parallel to the expected radial behaviour of the mass deposition rate derived from X-ray observations. Moreover, a large fraction (probably most ) of the cooling flow gas accreted into the emission-line region is converted into stars. In the light of this new data, we discuss the evolutionary sequence suggested by McNamara (1997), in which radio triggered star formation bursts take place several times during the lifetime of the cooling flow. We conclude that this scenario is consistent with the available observations.

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“…However, there can be no doubt that the impression of similarity was due to an over-interpreta tion of a small-scale photograph. Actually, NGC 1316 (see [6] is an early-type galaxy with some absorption patches which suggest the beginning of spiral formation, possibly of a barred spiral. NGC 5128 (see [7] seems to be a combination of an early-type system with the major axis in position angle about 45 0 and a late system containing much gas and dust in position angle about 135 0 .…”

Section: Single Galaxiesmentioning

confidence: 99%

“…Actually, NGC 1316 (see [6] is an early-type galaxy with some absorption patches which suggest the beginning of spiral formation, possibly of a barred spiral. NGC 5128 (see [7] seems to be a combination of an early-type system with the major axis in position angle about 45 0 and a late system containing much gas and dust in position angle about 135 0 . Moreover, NGC 5128 has a G-type absorption spectrum with emission lines strong enough to have been seen by Hubble on objective prism exposures.…”

Section: Single Galaxiesmentioning

confidence: 99%

17. Optical investigations of radio sources: Introductory Lecture

Minkowski

1957

Symp. - Int. Astron. Union

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Loose agreement of a radio position of low accuracy with that of some object listed in the NGC is not sufficient to provide the identification of a radio source. Even satisfactory coincidence of a precise position with that of an astronomical object requires supporting evidence. Agreement of the size of the source with that of the visible object, at least in order of magnitude, is an important argument in favour of an identification; exact agreement of sizes can be expected only where radio and optical emission are physically connected. The radio spectrum, the optical spectrum, and the physical characteristics of the visual object also have to be taken into account. Observations of the radio spectrum should be particularly useful to support the identification of sources with H 11 regions which can be recognized from their thermal emission even if they are obscured and optically inaccessible. If all data are available, satisfactory agreement exists between optical and radio observations. The best example of this kind at the moment is perhaps NGC 2237, the Rosette nebula, reported as a source by Ko and Krauss (1955) [1] and also observed by Mills, Little and Sheridan (1956 [11]; see also paper 18).

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On the Indentification of Radio Sources.

Cited by 204 publications

References 0 publications

12. The measurement of the distance of the radio sources

12. The measurement of the distance of the radio sources

Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows

17. Optical investigations of radio sources: Introductory Lecture

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