Abstract
Context. The evolution of galaxies through cosmic time is studied observationally by means of extragalactic surveys. The usefulness of these surveys is greatly improved by increasing the cosmological volume, in either depth or area, and by observing the same targets in different wavelength ranges. A multi-wavelength approach using different observational techniques can compensate for observational biases. Aims. The OTELO survey aims to provide the deepest narrow-band survey to date in terms of minimum detectable flux and emission line equivalent width in order to detect the faintest extragalactic emission line systems. In this way, OTELO data will complements other broad-band, narrow-band, and spectroscopic surveys. Methods. The red tunable filter of the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC) is used to scan a spectral window centred at 9175 Å, which is free from strong sky emission lines, with a sampling interval of 6 Å and a bandwidth of 12 Å in the most deeply explored EGS region. Careful data reduction using improved techniques for sky ring subtraction, accurate astrometry, photometric calibration, and source extraction enables us to compile the OTELO catalogue. This catalogue is complemented with ancillary data ranging from deep X-ray to far-infrared, including high resolution HST images, which allow us to segregate the different types of targets, derive precise photometric redshifts, and obtain the morphological classification of the extragalactic objects detected. Results. The OTELO multi-wavelength catalogue contains 11 237 entries and is 50% complete at AB magnitude 26.38. Of these sources, 6600 have photometric redshifts with an uncertainty δ zphot better than 0.2 (1+zphot). A total of 4336 of these sources correspond to preliminary emission line candidates, which are complemented by 81 candidate stars and 483 sources that qualify as absorption line systems. The OTELO survey results will be released to the public on the second half of 2019.
Highlights
Extragalactic surveys are an essential tool for studying galaxy evolution
The red tunable filter of the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC) is used to scan a spectral window centred at 9175 Å, which is free from strong sky emission lines, with a sampling interval of 6 Å and a bandwidth of 12 Å in the most deeply explored EGS region
Such pseudo-spectra were obtained by means of the red tunable filter (RTF) of the OSIRIS instrument at GTC
Summary
Extragalactic surveys are an essential tool for studying galaxy evolution. Considerable amounts of observing time have been invested, mainly in the last few decades, in gathering deeper and larger datasets, enriched with observations covering wide wavelength ranges, through the use of different instruments covering the same areas of sky. Mid-band surveys, with filter passbands of the order of ten to a few tens of nm, possibly with some overlapping of contiguous filters covering a relatively wide spectral band, represent an intermediate situation between the depth achieved in imaging, and the spectral coverage and resolution achieved in spectroscopy They are advantageous when the number of sources in the field is so large that the amount of time invested in observing through a large number of filters is comparable to, or lower than, what should be spent in gathering spectroscopic information (Benítez et al 2014).
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