view Abstract Citations (37) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Non-Thermal Optical Radiation from Galaxies Demoulin, Marie-Helene ; Burbidge, G. R. Abstract There is now observational evidence for non-thermal optical flux from the galaxies M87, M82, NGC 1068, NGC 4151, 3C 120, 3C 371, 3C 3903, and 3C 109. Estimates of the total flux emitted and its spectral energy distribution have been made from the observations. Upper limits to the size of the radiat- ing regions have been deduced from the variations of many of the sources. The energetics have been calculated for the three possible emission mechanisms: the electron and the proton synchrotron processes and Compton scattering. If the electron synchrotron process operates in the small sources, the minimum magnetic fields are ~O.1 gauss, greater than the equipartition value; total energies in particles and field are given in Table 2 for a variety of assumptions. If the proton synchrotron process operates, the mag- netic fields must be much stronger, `-~-`1O~ gauss, the proton energies are ~ eV, and the minimum total energies are 1O~-1O~ times those for the electron synchrotron process, while the Compton effect is negligible; however, the ambient gas density must be <1O~ particles cm3. If the optical flux is Compton radiation generated by the interaction of high-energy electrons with an intense radiation field of lower frequency (some part of the high-frequency radio flux), the process is found to be highly inefficient, since a large flux of electrons is required and only a small fraction of their energy will be transferred in the time taken to cross the source. This process is open to observational test, since in most cases a much larger flux of harder radiation (X-rays or `y-rays) will be generated. It is concluded that the electron synchrotron process is likely to be the most efficient for the genera- tion of the non-thermal optical flux. Observations in many frequency ranges (radio, infrared, optical, and X-ray) of the same sources and their variable properties may enable us to eliminate some processes. Finally, a comparison is made between these galaxies and quasi-stellar objects. It is shown that the similarities between QSOs and Seyfert and N-type galaxies do not support either the local or the cosmo- logical interpretation of the QSOs. In either case the properties are continuous Publication: The Astrophysical Journal Pub Date: October 1968 DOI: 10.1086/149736 Bibcode: 1968ApJ...154....3D full text sources ADS | data products NED (8)