Spectroscopy of 7 radio-loud QSOs at 2 < z < 6: giant Lyman alpha emission nebulae accreting on to host galaxies

N. Roche, A. Humphrey, L. Binette

Abstract
We performed long-slit optical spectroscopy (Gran Telescopio Canarias-Optical System for Imaging and low Resolution Integrated Spectroscopy) of 6 radio-loud quasi-stellar objects (QSOs) at redshifts 2 < z < 3, known to have giant (∼50–100 kpc) Lyman α emitting nebulae, and detect extended Lyman α emission for 4, with surface brightness ∼10⁻¹⁶ erg cm⁻² s⁻¹ arcsec⁻² and line full width at half-maximum 400–1100 (mean 863) km s^{− 1}. We also observed the z ≃ 5.9 radio-loud QSO, SDSS J2228+0110, and found evidence of a ≥10 kpc extended Lyman α emission nebula, a new discovery for this high-redshift object. Spatially resolved kinematics of the 5 nebulae are examined by fitting the Lyman α wavelength at a series of positions along the slit. We found the line-of-sight velocity Δ(v) profiles to be relatively flat. However, 3 of the nebulae appear systematically redshifted by 250–460 km s^{− 1} relative to the Lyman α 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 (∼100 km 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.

Keywords
ISM: kinematics and dynamics, galaxies: active, galaxies: high-redshift, quasars: absorption lines, quasars: emission lines

Monthly Notices of the Royal Astronomical Society
Volume 443, Page 3795
October 2014

>> ADS>> DOI