Lyα emission in high-redshift galaxies^*

¹ Landessternwarte Heidelberg-Königstuhl, 69117 Heidelberg, Germany
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: tapken@mpia.de
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85741 Garching, Germany
⁴ Institut d' astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
⁵ Institut für Theoretische Astrophysik, Albert-Ueberle-Straße 2, 69120 Heidelberg, Germany

Received: 14 June 2006
Accepted: 5 February 2007

Abstract

Context. A significant fraction of the high-redshift galaxies show strong  emission lines. For redshifts , most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects.

Aims.Our aim is to analyse the  emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the  profile and the line strength.

Methods. VLT/FORS spectra with a resolution of R ≈ 2000 of 16 galaxies in the redshift range of to 5 are presented. The observed  profiles are compared with theoretical models.

Results.The   lines range from pure absorption ( Å) to strong emission ( Å). Most  emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform model consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation rates of these galaxies ranging from = 1.2 to 63.2 yr^-1 uncorrected for dust absorption.

Conclusions.The  emission strength of our target galaxies is found to be determined by the amount of dust and the kinematics of the outflowing material.