Kinematically quiet haloes around z ∼ 2.5 radio galaxies. Keck spectroscopy

We present the results of the kinematic study of the extended gas in a sample of 10 high-redshift radio galaxies (z ∼ 2.5) based on high signal-to-noise ratio Keck II and Very Large Telescope (VLT) long-slit spectroscopy. In addition to the typical high surface brightness kinematically perturbed regions (FWHM and velocity shifts > 1000 km s - 1 ), we find in all objects giant low surface brightness haloes that show quieter kinematics with typical emission-line FWHM and velocity shifts of ∼several hundred km s - 1 . The giant haloes often extend for more than 100 kpc and sometimes beyond the radio structures. They emit lines other than Lya (C IV, He II and Nv in some cases), typically found in the spectra of high-redshift active galaxies. Continuum is also often detected. The haloes are enriched with heavy elements at tens of kpc from the active nucleus. Typical Lya luminosities and surface brightness (within the slit) are in the range 10 4 3 - 4 4 erg s - 1 and several × 10 - 1 7 t o - 1 6 erg cm - 2 s - 1 arcsec - 2 , respectively. Estimated densities are in the range ∼17-150 cm - 3 . The quasar continuum is the dominant source of ionization of the quiescent haloes along the radio axis. The implied total quasar ionizing luminosities are in the range ∼ several × 10 4 5 -10 4 7 erg s - 1 , in the same range as radio-loud quasars at comparable redshift. The detection of giant quiescent haloes in all objects suggests that they could be a common ingredient of high-redshift radio galaxies. The radio galaxies seem to be embedded within the haloes. The nature and the origin of the haloes, together with the cosmological implications, are also discussed.