EDP Sciences
Free access
Volume 430, Number 3, February II 2005
Page(s) 877 - 891
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20035863

A&A 430, 877-891 (2005)
DOI: 10.1051/0004-6361:20035863

The expected abundance of Lyman- $\alpha$ emitting primeval galaxies

I. General model predictions
E. Thommes1, 2 and K. Meisenheimer1

1  Max, Planck, Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
    e-mail: E.Thommes@thphys.uni-heidelberg.de
2  Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany

(Received 15 December 2003 / Accepted 1 October 2004)

We present model calculations for the expected surface density of Ly- $\alpha$ emitting primeval galaxies (PGs) at high redshifts. We assume that elliptical galaxies and bulges of spiral galaxies (=spheroids) formed early in the universe and that the Ly- $\alpha$ emitting PGs are these spheroids during their first burst of star formation at high redshift. One of the main assumptions of the models is that the Ly- $\alpha$ bright phase of this first starburst in the spheroids is confined to a short period after its onset due to rapid formation of dust. The models do not only explain the failure of early surveys for Ly- $\alpha$ emitting PGs but are also consistent with the limits of new surveys (e.g. the Calar Alto Deep Imaging Survey - CADIS). At faint detection limits $S_{{\rm lim}} \le
10^{-20}$  W m -2 the surface density of Ly- $\alpha$ emitters is expected to vary only weakly in the redshift range between z=3 and z=6 with values > $10^3 / {\rm deg}^2 / \Delta z = 0.1 $ reaching its maximum at $z_0 \approx 4$. At shallower detection limits, $S_{{\rm lim}} \ge 3\times 10^{-20}$ W m -2 the surface density of high- z Ly- $\alpha$ emitters is expected to be a steep function of redshift and detection limit. This explains the low success in finding bright Ly- $\alpha$ galaxies at z > 5. We demonstrate how the observed surface densities of Ly- $\alpha$ emitting PGs derived from recent surveys constrain the parameters of our models. Finally, we discuss the possibility that two Ly- $\alpha$ bright phases occur in the formation process of galaxies: An initial - primeval - phase in which dust is virtually non-existant, and a later secondary phase in which strong galactic winds as observed in some Lyman break galaxies facilitate the escape of Ly- $\alpha$ photons after dust has already been formed.

Key words: galaxies: formation -- surveys -- galaxies: high-redshift -- X-ray: stars

© ESO 2005