EDP Sciences
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Volume 467, Number 1, May III 2007
Page(s) 63 - 72
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20065825

A&A 467, 63-72 (2007)
DOI: 10.1051/0004-6361:20065825

Ly$\alpha$ emission in high-redshift galaxies

C. Tapken1, 2, I. Appenzeller1, S. Noll3, S. Richling4, J. Heidt1, E. Meinköhn5, and D. Mehlert2

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)

Context. A significant fraction of the high-redshift galaxies show strong ${\rm Ly}{\alpha}$ emission lines. For redshifts z > 5, 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 ${\rm Ly}{\alpha}$ emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the ${\rm Ly}{\alpha}$ profile and the line strength.
Methods. VLT/FORS spectra with a resolution of R $\approx$ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed ${\rm Ly}{\alpha}$ profiles are compared with theoretical models.
Results.The ${\rm Ly}{\alpha}$ lines range from pure absorption (EW = -17 Å) to strong emission (EW = 153 Å). Most ${\rm Ly}{\alpha}$ 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 $SFR_{\rm {UV}}$ = 1.2 to 63.2 $M_{\odot}$yr-1 uncorrected for dust absorption.
Conclusions.The ${\rm Ly}{\alpha}$ emission strength of our target galaxies is found to be determined by the amount of dust and the kinematics of the outflowing material.

Key words: galaxies: high-redshift -- galaxies: ISM -- galaxies: emission lines

© ESO 2007