view Abstract Citations (141) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ionized Gas in Spiral and Irregular Galaxies. Burbidge, E. Margaret ; Burbidge, G. R. Abstract The distribution of ionized gas as deduced from the emission lines seen with the nebular spectrograph is described for more than 30 spiral and irregular galaxies. From the comparison of estimates of the relative intensities of Ha and [N ii] X 6583, with relative intensities computed by the usual techniques, it is concluded that the major regions of emission in the outer parts of galaxies and in the spiral arms, where the Ha/[N ii] X 6583 ratio is 3, are similar to the extended H ii regions first discovered by Struve and Elvey in our own Galaxy. The investigation has substantiated the result that irregular galaxies have the highest proportion of ionized gas and that this decreases steadily through barred spirals of types SBc and SBb and normal spirals of types Sc, Sbc, Sb, and Sa. Throughout irregular galaxies and in the nuclear, as well as the spiral-arm, regions of SBc and SBb galaxies and some Sbc and Sc galaxies there must be a considerable population of massive luminous stars. The nuclei of other Sc and Sbc galaxies and the nuclei in the majority of Sb galaxies contain less ionized gas than do the spiral-arm regions. The most striking observational result is that between the outer parts and the nuclear regions in many of these latter galaxies the ratio of the strengths of Ha and [N ii] X 6583 decreases from about 3 to values in the range 10.1. This reversal is most common in Sb and Sa galaxies with large prominent nuclei and well-developed nuclear bulges, but it appears even in some Sc galaxies with small nuclei. This can be explained either by a general deficiency of hydrogen in these regions (which we think improbable) or by supposing that radiative processes are comparatively unimportant in those nuclei where the light comes mainly from K giants, and that collisional ionization and excitation take place in the gas with an electron temperature of , or with energies of a few electron volts, since such excitation may be non-thermal. These excitation conditions might arise through corpuscular radiation from . Whether such an explanation for the anomalous ratios is accepted depends on the energy balance, i.e., estimates of the energy supply required to maintain such a high electron temperature against cooling mainly by line emission. This will require absolute measurement of emission4ine intensities. Publication: The Astrophysical Journal Pub Date: May 1962 DOI: 10.1086/147313 Bibcode: 1962ApJ...135..694B full text sources ADS | data products SIMBAD (42) NED (36)