The hydrogen line spectra of narrow-line radio galaxies.

Abstract

The results of the first detection of Ly-alpha in a narrow-line radio galaxy are reported. Nearly simultaneous optical and UV observations of 3C 192 and 3C 223 allow the measurement of both Balmer and Lyman decrements. These line ratios are approximate functions of the interstellar reddening and of a parameter which is proportional to the amount of H I collisional excitation present. The reddening of 3C 192 is slightly larger than that due to the Galaxy, although 3C 223 may have a larger value. Both galaxies have intrinsic Balmer and Lyman decrements which are significantly steeper than case B, suggesting that the gas is photoionized by a fairly hard X-ray continuum. The deduced values of L-alpha/H-beta and H-alpha/H-beta compare favorably with predictions of recent models.