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Issue A&A
Volume 459, Number 3, December I 2006
Page(s) 717 - 729
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20065318



A&A 459, 717-729 (2006)
DOI: 10.1051/0004-6361:20065318

Extended Lyman-$\alpha$ emission around bright quasars

L. Christensen1, 2, K. Jahnke2, 3, L. Wisotzki2, and S. F. Sánchez4

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 Ly$\alpha$ emission line regions (EELRs) around seven bright, mostly radio-quiet quasars (QSOs) at 2.7<z<4.5, 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 Ly$\alpha$ 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 Ly$\alpha$ 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 3-4´´ from the QSO and surface flux densities up to 2- $3\times10^{-16}$  erg cm-2 s-1 arcsec-2. The five EELRs have total Ly$\alpha$ luminosities which correspond to ~0.5% of the luminosities from the QSOs broad Ly$\alpha$ 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 Ly$\alpha$ 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 Ly$\alpha$ 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.


Key words: galaxies: active -- galaxies: high-redshift -- galaxies: quasars: emission lines



© ESO 2006


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