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

¹ INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monteporzio Catone, Italy
e-mail: laura.pentericci@oa-roma.inaf.it
² INAF, Osservatorio Astronomico di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
³ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
⁴ Department of Physics, University of California, 1 Shields Ave, Davis, CA 95616, USA
⁵ School of Physics & Astronomy,The University of Nottingham, University Park, Nottingham NG7 2RD, UK
⁶ INAF-Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁷ NOAO, 959 N. Cherry Ave, Tucson, AZ 85719, USA
⁸ Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA
⁹ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
¹⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
¹¹ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹² School of Earth & Space Exploration, Arizona State University, Tempe, AZ 85287, USA

Received: 15 December 2017
Accepted: 3 August 2018

Abstract

We present the results of CANDELSz7, a European Southern Observatory (ESO) Large Program aimed at spectroscopically confirming 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 h to reach a Lyα flux limit of approximately 1 − 3 × 10⁻¹⁸ erg s⁻¹ cm⁻² at 3σ. We could determine a spectroscopic redshift for about 40% of the galaxies, mainly through the detection of a single emission line that we interpret as Lyα emission, or for some of the brightest objects (H₁₆₀ ≤ 25.5) from the presence of faint continuum and a sharp drop that we interpret as a Lyα 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 Lyα 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.