CANDELSz7: a large spectroscopic survey of CANDELS galaxies in the reionization epoch

TL;DR

This study presents spectroscopic confirmation of 65 high-redshift galaxies at z~6-7 from the CANDELS survey, analyzing their properties and the evolution of Lyalpha emission during reionization.

Contribution

It provides a large, homogeneous spectroscopic sample of z~6-7 galaxies, improving understanding of galaxy evolution and Lyalpha emission during reionization.

Findings

Confirmed 65 new high-redshift galaxies spectroscopically.

Analyzed Lyalpha fraction evolution between z~6 and z~7.

Assessed photometric redshift accuracy in the reionization epoch.

Abstract

We present the results of CANDELSz7, an ESO large program aimed at confirming spectroscopically a homogeneous sample of z~6 and z~7 star forming galaxies. The candidates were selected in the GOODS-South, UDS and COSMOS fields using the official CANDELS catalogs based on H160-band detections. Standard color criteria, which were tailored depending on the ancillary multi-wavelength data available for each field, were applied to select more than 160 candidate galaxies at z~6 and z~7. Deep medium resolution FORS2 spectroscopic observations were then conducted with integration times ranging from 12 to 20 hours, to reach a Lyalpha flux limit of approximately 1-3x 10-18 erg/s/cm^2 at 3sigma. For about 40% of the galaxies we could determine a spectroscopic redshift, mainly through the detection of a single emission line that we interpret as Lyalpha emission, or for some of the brightest objects (H160< 25.5) from the presence of faint continuum and sharp drop that we interpret as a Lyman break. In this paper we present the redshifts and main properties of 65 newly confirmed high redshift galaxies. Adding previous proprietary and archival data we assemble a sample of ~260 galaxies that we use to explore the evolution of the Lyalpha fraction in Lyman break galaxies and the change in the shape of the emission line between z~6 and z~7. We also discuss the accuracy of the CANDELS photometric redshifts in this redshift range.