The Wide Field Imager Lyman-Alpha Search (WFILAS) for galaxies at redshift ~5.7: II. Survey design and sample analysis

Context. Wide-field narrowband surveys are an efficient way of searching large volumes of high-redshift space for distant galaxies. Aims. We describe the Wide Field Imager Lyman-Alpha Search (WFILAS) over 0.74 sq. degree for bright emission-line galaxies at z ∼ 5.7. Methods. WFILAS uses deep images taken with the Wide Field Imager (WFI) on the ESO/MPI 2.2 m telescope in three narrowband (70 A), one encompassing intermediate band (220 A) and two broadband filters, B and R. We use the novel technique of an encompassing intermediate band filter to exclude false detections. Images taken with broadband B and R filters are used to remove low redshift galaxies from our sample. Results. We present a sample of seven Lyα emitting galaxy candidates, two of which are spectroscopically confirmed. Compared to other surveys all our candidates are bright, the results of this survey complements other narrowband surveys at this redshift. Most of our candidates are in the regime of bright luminosities, beyond the reach of less voluminous surveys. Adding our candidates to those of another survey increases the derived luminosity density by ∼30%. We also find potential clustering in the Chandra Deep Field South, supporting overdensities discovered by other surveys. Based on a FORS2/VLT spectrum we additionally present the analysis of the second confirmed Lyα emitting galaxy in our sample. We find that it is the brightest Lyα emitting galaxy (1 x 10 -16 erg s -1 cm -2 ) at this redshift to date and the second confirmed candidate of our survey. Both objects exhibit the presence of a possible second Lyα component redward of the line.