This paper describes the observations and the first data release (DR1) of the ESO public spectroscopic survey "VANDELS, a deep VIMOS survey of the CANDELS CDFS and UDS fields". VANDELS’ main targets are star-forming galaxies at redshift 2.4 < z < 5.5, an epoch when the Universe was less than 20% of its current age, and massive passive galaxies in the range 1 < z < 2.5. By adopting a strategy of ultra-long exposure times, ranging from a minimum of 20 hours to a maximum of 80 hours per source, VANDELS is specifically designed to be the deepest ever spectroscopic survey of the high-redshift Universe. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the survey is obtaining ultra-deep optical spectroscopy covering the wavelength range 4800-10000 Å with sufficient signal-to-noise to investigate the astrophysics of high-redshift galaxy evolution via detailed absorption line studies of well defined samples of high-redshift galaxies. The VANDELS-DR1 is the release of all medium-resolution spectroscopic data obtained during the first season of observations, on a 0.2 square degree area centered around the CANDELS-CDFS and CANDELS-UDS areas. It includes data for all galaxies for which the total (or half of the total) scheduled integration time was completed. The data release contains 879 individual objects, approximately half in each of the two fields, which have a measured redshift, with the highest reliable redshifts reaching zspec ∼ 6. In the data release we include fully wavelength and flux-calibrated 1D spectra, the associated error spectrum and sky spectrum and the associated wavelength-calibrated 2D spectra. We also provide a catalogue with the essential galaxy parameters, including spectroscopic redshifts and redshift quality flags measured by the collaboration. In this paper we present the survey layout and observations, the data reduction and redshift measurement procedure and the general properties of the VANDELS-DR1 sample. In particular we discuss the spectroscopic redshift distribution, the accuracy of the photometric redshifts for each individual target category and we provide some examples of data products for the various target types and the different quality flags. All VANDELS-DR1 data are publicly available and can be retrieved from the ESO archive. Two further data releases are foreseen in the next two years with a final data release currently scheduled for June 2020 which will include improved re-reduction of the entire spectroscopic data set. . .
|Original language||English (US)|
|State||Published - Mar 20 2018|
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