OTELO (OSIRIS Tunable Emission Line Object survey) is a deep emission-line survey which takes advantage of Tunable Filter (TF) facility of the intrument OSIRIS on GTC, an unique facility in 8-10m class telescopes. The TFs had been configured to cover a selected atmospheric window (around 8950-9300 Å) relatively free of sky emission lines [1]. The survey produces 3D data cubes (proyected position + wavelength) from which a pseudo spectra can be extracted. The pseudo spectra is obtained from, typically, 36 TF images (filter width of 12  Å) at wavelengths covering a spectral range of 230 Å with a spectral of R ∼ 700.

Thanks to the use of ancillary data to estimate the redshift of the source, it is possible to identify the observed emission lines, (including the deblending of Hα from the [NII]λ658.3,654.8 nm lines at redshift z ∼ 0.4), allowing to determine the nature and physical properties of the different sources.

The survey studies a defined volume of the Universe with a 5σ depth of 1x10-18 erg.cm-2.s-1, which makes OTELO one of the deepest emission-line survey to date.

The figure shows some examples of OTELO emission line pseudo-spectra at the region around [O III]λ495.9 + 500.7 nm @ z ∼ 0.8; the Hα λ656.3 nm and [NII]λ658.3,654.8 nm lines @ z ∼ 0.4; or an object with an isolated emission line (to be analyzed).

OTELO in numbers
Property Value
Centre coordinates
α: 14h17m20s,
δ: +52ª 27' 50"
Spatial coverage 56 arcmin2
Sampling interval
6 Å
(Hα + NII deblending)
Wavelength accusracy 1 Å
Limiting magnitude
3 σ, 50% completeness
26.53 AB
Minimun EW 5 Å
Photometric acurracy S/N > 2 +/-0.05 mag
Redshift accuracy ~5% up to z=1.4
Ancillary data Deep X-Ray to FIR (500 microm)
Source counting
Total sources extracted 11.237
Bona fide emitters 1.030
Candidate emitters 2.253
Bona fide absorberes 147

Tunable Filters and OTELO psudospectra

Figure: Examples of OTELO pseudo-spectra: Top-left: Region around [O III]λ495.9 + 500.7 nm @ z ∼ 0.8; Bottom-right: Region around the Hαλ656.3 nm and the [NII]λ658.3,654.8 nm lines @ z ∼ 0.4; Bottom-left: Isolated emission line (to be analyzed)

top-right: squematic view of TF technique; figure adapted from Jones, Shopbell & Bland-Hawthorn (2002) MNRAS 329, 759

Keywords: GTC - OSIRIS - Tunable Filters - Emission Line objects



[1] Sky lines at the ORM, where GTC is sited, and wavelength covered by OTELO survey.