Spectroscopy of 7 Radio-Loud QSOs at 2<z<6: Giant Lyman-alpha Nebulae Accreting onto Host Galaxies

Abstract

We performed long-slit optical spectroscopy (GTC-OSIRIS) of 6 radio-loud QSOs at redshifts \(2<z<3\), known to have giant (\(\sim 50\)-100 kpc) Lyman-\(\alpha\) emitting nebulae, and detect extended Lyman-\(\alpha\) emission for 4, with surface brightness \(\sim10^{-16}\) ergs \(\rm cm^{-2}s^{-1}arcsec^{-2}\) and line width FWHM 400-1100 (mean 863) km \(\rm s^{-1}\). We also observed the \(z\simeq 5.9\) radio-loud QSO, SDSS J2228+0110, and find evidence of a \(\geq 10\) kpc extended Lyman-\(\alpha\) emission nebula, a new discovery for this high-redshift object. Spatially-resolved kinematics of the 5 nebulae are examined by fitting the Lyman-\(\alpha\) wavelength at a series of positions along the slit. We found the line-of-sight velocity \(\Delta(v)\) profiles to be relatively flat. However, 3 of the nebulae appear systematically redshifted by 250-460 km \(\rm s^{-1}\) relative to the Lyman-\(\alpha\) line of the QSO (with no offset for the other two), which we argue is evidence for infall. One of these (Q0805+046) had a small (\(\sim 100\) km \(\rm s^{-1}\)) velocity shift across its diameter and a steep gradient at the centre. Differences in line-of-sight kinematics between these 5 giant nebulae and similar nebulae associated with high-redshift radio galaxies (which can show steep velocity gradients) may be due to an orientation effect, which brings infall/outflow rather than rotation into greater prominence for the sources observed `on-axis' as QSOs.