The OTELO survey

Abstract

Context. The OSIRIS Tunable Filter Emission Line Object (OTELO) survey is a very deep, blind exploration of a selected region of the Extended Groth Strip and is designed for finding emission-line sources (ELSs). The survey design, observations, data reduction, astrometry, and photometry, as well as the correlation with ancillary data used to obtain a final catalogue, including photo-z estimates and a preliminary selection of ELS, were described in a previous contribution. Aims. Here, we aim to determine the main properties and luminosity function (LF) of the [O III] ELS sample of OTELO as a scientific demonstration of its capabilities, advantages, and complementarity with respect to other surveys. Methods. The selection and analysis procedures of ELS candidates obtained using tunable filter pseudo-spectra are described. We performed simulations in the parameter space of the survey to obtain emission-line detection probabilities. Relevant characteristics of [O III] emitters and the LF ([O III]), including the main selection biases and uncertainties, are presented. Results. From 541 preliminary emission-line source candidates selected around z = 0.8, a total of 184 sources were confirmed as [O III] emitters. Consistent with simulations, the minimum detectable line flux and equivalent width in this ELS sample are ∼5 × 10−19 erg s−1 cm2 and ∼6 Å, respectively. We are able to constrain the faint-end slope (α = −1.03 ± 0.08) of the observed LF ([O III]) at a mean redshift of z = 0.83. This LF reaches values that are approximately ten times lower than those from other surveys. The vast majority (84%) of the morphologically classified [O III] ELSs are disc-like sources, and 87% of this sample is comprised of galaxies with stellar masses of M⋆ < 1010 M⊙.

The OTELO survey

“…Other works have used the combination of Hβ and [O iii], for example De Barros et al (2019) reaching as far as z ∼ 8; Khostovan et al (2015) up to 0.84 < z < 3.24; and Sobral et al (2015) up to z = 1.4. In addition, there are a series of works were the LF is obtained by employing the doublet [O iii] λλ4959,5007 alone, for example, in Ly et al (2007) at 0.41 < z < 0.84; Bongiovanni et al (2020) at z ∼ 0.83; Khostovan et al (2020) at 0.91 < z < 1.10; or Hayashi et al (2020) at 0.05 < z < 0.94.…”

The OTELO survey

“…We note that by construction, the inverse deconvolution process always provides a solution for the intensity of the f [N II] λ6583 value, which would correspond to a 12 + log(O/H) = 7.63 (before the stellar absorption correction). These values would be below the OTELO line flux limit of 5 × 10 −19 erg −1 s −1 cm −2 as occurs for five objects (see Bongiovanni et al 2020, for the flux limit estimation). These cases translate into a large uncertainty in the resulting N2 and metallicity values.…”

“…The redshift value obtained for each source after deconvolution (hereafter z OTELO ) are given in Table B.1. Formally, the common maximum uncertainty of these values is about 0.001(1 + z OTELO ), as established in Bongiovanni et al (2020).…”

“…It is worth noting that the OTELO sample is three orders of magnitude deeper in stellar mass than the two surveys at similar redshift. This is due to the depth of the OTELO survey (line flux down to 5.6 × 10 −19 erg −1 s −1 cm −2 , see Bongiovanni et al 2020) and its potential as a blind spectroscopic survey to pre-select ELSs according to their PS and not only as a result of the colour excess in the colour-magnitude diagram. In Fig.…”

“…To this aim, we used data from the OSIRIS Tunable filter Emission-Line Object (OTELO) survey reported by Bongiovanni et al (2019, hereafter OTELO-I) to study a sample of low-mass Hα emission line sources (ELS) at redshift ∼0.4, firstly described in Ramón-Pérez et al (2019, hereafter OTELO-II). As demonstrated in Bongiovanni et al (2020), OTELO has allowed validation of the narrow-band (NB) scan technique using tunable filters (TFs) for finding faint populations of SFGs, which makes this survey the most sensitive to date in terms of minimum emission-line flux (∼5 × 10 −19 erg s −1 cm −2 ) and observed equivalent width (EW ≈ 6 Å) achieved.…”