Extended Lyman-α emission around bright quasars

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: lichrist@eso.org
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Centro Astronomico Hispano Aleman de Calar Alto, Calle Jesus Durbán Remón 2,2 04004 Almeria, Spain

Received: 29 March 2006
Accepted: 3 August 2006

Abstract

Context.Quasars trace the most massive structures at high redshifts and their presence may influence the evolution of the massive host galaxies.

Aims.We study the extended Lyα emission line regions (EELRs) around seven bright, mostly radio-quiet quasars (QSOs) at , and compare luminosities with EELRs around radio-loud QSOs reported in the literature.

Methods. Using integral field spectroscopy, we analyse the morphology and kinematics of the quiescent Lyα EELRs around the QSOs.

Results. We find evidence for the presence of EELRs around four radio-quiet and one radio-loud QSO. All EELRs appear asymmetric and the optically brightest QSOs also have the brightest Lyα nebulae. For the two brightest nebulae we find velocities between ~600 km s^-1 at the QSO position to ~200 km s^-1 at a distance of ´´ from the QSO and surface flux densities up to 2–  erg cm^-2 s^-1 arcsec^-2. The five EELRs have total Lyα luminosities which correspond to ~0.5% of the luminosities from the QSOs broad Lyα emission lines. This fraction is an order of magnitude smaller than found for EELRs around radio-loud, steep spectrum QSOs reported in the literature. While the nebulae luminosities are correlated with the QSO Lyα luminosities, we find that nebulae luminosities are not correlated with the central QSO ionising fluxes.

Conclusions. The presence of gas in the EELRs can be interpreted based on two competing scenarios: either from quasar feedback mechanisms, or from infalling matter. Apart from these two effects, the Lyα flux around radio-loud objects can be enhanced due to interactions with the radio jets. The relatively fainter nebulae around radio-quiet QSOs compared to lobe-dominated radio-loud QSOs can be ascribed to this effect, or to significant differences in the environments between the two classes.