The OTELO survey. I. Description, data reduction, and multi-wavelength
  catalogue
  The evolution of galaxies through cosmic time is studied observationally by
means of extragalactic surveys. 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. 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 $9175 \AA$, which is free from strong sky emission
lines, with a sampling interval of $6 \AA$ and a bandwidth of $12 \AA$ in the
most deeply explored Extended Groth Strip 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.
The OTELO multi-wavelength catalogue contains 11237 entries and is 50\%
complete at AB magnitude 26.38. Of these sources, 6600 have photometric
redshifts with an uncertainty $z_{phot}$ better than $0.2 (1+z_{phot})$. 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 products were released to
the public on 2019.
