17. Optical investigations of radio sources: Introductory Lecture

Abstract

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).

A relation between circumnuclear H I, dust, and optical cores in low-power radio galaxies

“…This source is known to have a galaxy in the line of sight. This was first discussed by Minkowski (1957) and later confirmed by Lynds (1970). Two separate H i absorption components are seen.…”

NGC 1275: Baryonic cycing in the Perseus cluster of galaxies

“…That this is an impressively complicated situation is further illustrated by Minkowski's (1957) discovery of a a second emission line system redshifted by 3000 km s −1 , now interpreted to be an infalling galaxy in the foreground of NGC 1275.…”

Observational Signatures of Particle Acceleration in Supernova Remnants

“…A supernova with hydrogen lines in its spectrum is classified as a type II, and without is classified as a type I (Minkowski, 1941). More specifically, a spectrum without hydrogen lines but with strong Si II lines is classified as a type Ia spectrum, without Si II lines but with strong helium I lines as type Ib and if the spectra are lacking both strong Si II and He I lines, the supernova is classified as a type Ic.…”