Constraints to the evolution of Ly-α bright galaxies between z = 3 and z = 6^*

¹ Max–Planck–Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² Insitut für Theoretische Physik, Universität Heidelberg, 69111 Heidelberg, Germany
³ Department of Physics, Denys Wilkinson Bldg., University of Oxford, Keble Road, Oxford, OX1 3RH, UK

Corresponding author: C. Maier, maier@mpia-hd.mpg.de

Received: 6 November 2002
Accepted: 4 February 2003

Abstract

Galaxies at high redshift with a strong Ly-α emission line trace massive star formation in the absence of dust, and can therefore be regarded as a prime signature of the first major starburst in galaxies. We report results of the Ly-α  search within the Calar Alto Deep Imaging Survey (CADIS). With the imaging Fabry-Perot interferometer, CADIS can detect emission lines in three waveband windows free of night-sky emission lines at 700 nm, 820 nm, and 920 nm. The typical flux detection limit for Ly-α  emission redshifted into these windows, , corresponds to (unobscured) star formation rates of /yr at . Candidate Ly-α-emitting galaxies are selected from the total emission line sample, which contains more than 97% of objects at , by the absence of flux below the Lyman limit (B-band “dropouts”), and the non-detection of secondary emission lines in narrow band filters. We have detected 5 bright Ly-α-emitting galaxy candidates at , and 11 candidates at . For two of four observed Ly-α candidates, one candidate at , and the other at , the emission line detected with the Fabry-Perot interferometer has been verified spectroscopically at the VLT.
When compared to Ly-α  surveys at , even the upper limits set by our list of candidates show that bright Ly-α  galaxies are significantly rarer at than the assumption of a non-evolving population would predict. Therefore we conclude that the Ly-α  bright phase of primeval star formation episodes reached its peak at redshifts .