Far UV study on the non-thermal activity in the narrow line galaxies NGC 4507 and NGC 5506.

Abstract

The narrow line high excitation galaxies NGC 4507 and NGC 5506 were observed with IUE satellite in the low resolution mode. The continua of both galaxies, when combined with optical observations, show a flattening at log nu greater than 14.9. The reddening correction cannot be estimated with accuracy. The energy content in the Lyman continuum is large enough to power the narrow line region, provided the coverage factor is of the order of unity. In the case of NGC 4507, good signal-to-noise ratio is available for line study. In comparison to broad line region in active nuclei it is found that NGC 4507 is characterized by: (1) much larger intensities of the recombination lines Ly-alpha and He II 1640 relative to C IV and (2) a Ly-Alpha/H-beta ratio of 17 to 27, depending on the chosen reddening correction, implying much smaller opacities in the Lyman lines of H. The opacity in the Balmer lines of both H I and He II is small, as derived from the H Balmer decrement and the He II 1640/He II 4686 intensity ratio.