Strong Lyman-alpha emission in three distant radio galaxies

Abstract

The authors have discovered very strong narrow Lyα emission in the redshifted ultraviolet spectra of three radio galaxies having 1.62 ⪉ z ⪉ 1.82. The spectra of 3C 256 and 3C 239 are almost identical; besides Lyα, the strongest UV emission lines are C IV λ1549, He II λ1640, and C III] λ1909. The galaxy 3C 241 exhibits similar features, but the data are of poorer quality. The luminosity of Lyα is typically ≡2×10<SUP>44</SUP>ergs s<SUP>-1</SUP> (H<SUB>0</SUB> = 50 km s<SUP>-1</SUP>Mpc<SUP>-1</SUP>, q<SUB>0</SUB> = 0), while its intrinsic full width at half-maximum is ≡1500 km s<SUP>-1</SUP>. Differences between the average spectrum of the radio galaxies and that of QSOs with z ⪆ 2 are briefly discussed.