1999A&A...351...47V

We present UV spectra of a small sample of high redshift active galaxies: the hyperluminous, gravitationally lensed system SMM J02399-0136 (z=2.8) and three powerful radio galaxies (z∼2.5). Extended continuum and emission lines are detected in all objects. The three radio galaxies present typical spectra with dominant Lyα and weaker CIVλ1550, HeIIλ1640 and CIII]λ1909. The spectrum of SMM J02399-0136 is strikingly different, showing relatively weak Lyα and HeII and strong NVλ1240 relative to the C lines. We find that the weakness of HeII can be explained if the intermediate density narrow line region (n∼10^5–6cm^–3) dominates the emission line spectrum, rather than the more extended low density gas (n≤100cm^–3). The line ratios of MRC 2025-218 suggest that this is also the case in this object. MRC 2025-218 and SMM J02399-0136 show the largest NV/HeII and NV/CIV values found in high redshift radio galaxies. The failure of solar abundance models to explain these line ratios and studies of metal abundances in high redshift quasars and radio galaxies suggest that nitrogen is overabundant in the ionized gas of these objects. Alternative possibilities which we discuss include NV emission from the broad line region and differential amplification by a gravitational lens. We report the discovery of a P Cygni profile in the CIV line in the spectrum of MRC 2025-218. We detect also CIIλ1334.5 in absorption and P Cygni profiles for the lines SiIVλλ1393.8,1402.8. We do not detect any purely photospheric stellar lines. The nature of the absorption features is not clear. It could be due to stars or an associated absorption line system.