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RevMexAA (Serie de Conferencias), 42, 70–72 (2013)

THE OTELO PROJECT

J. Cepa,1,2 A. Bongiovanni,1,2 A. M. Perez Garcıa,1,2 A. Ederoclite,1,2 M. A. Lara-Lopez,1,2,3 E. J. Alfaro,4

J. Gallego,5 J. J. Gonzalez,6 J. I. Gonzalez-Serrano,7 M. Sanchez-Portal,8 H. O. Castaneda,9

J. Bland-Hawthorn,10 J. M. Rodrıguez-Espinosa,1,2 M. Fernandez-Lorenzo,4 and M. Povic4

RESUMEN

El Proyecto OTELO es el cartografiado extragalactico que se desarrolla mediante los filtros sintonizables delinstrumento OSIRIS del GTC. Ya esta proporcionando el cartografiado mas profundo de galaxias en emisionque existe, hasta un desplazamiento al rojo de 7. En esta contribucion, se presenta el estado del cartografiado,ası como algunos resultados preliminares obtenidos.

ABSTRACT

The OTELO Project is an extragalactic survey under way using the tunable filters of the instrument OSIRISat the GTC. OTELO is already providing the deepest emission line survey of the universe up to a redshift 7.In this contribution, the status of the survey and the first preliminary results obtained will be presented.

Key Words: galaxies: abundances — galaxies: evolution — galaxies: high-redshift — methods: observational — surveys

— techniques: imaging spectroscopy

1. INTRODUCTION

OTELO is an emission line survey using the Tun-able Filters (TF) of the instrument OSIRIS at the10.4 m GTC telescope. The OSIRIS TFs allow ob-taining narrow band images anywhere within theOSIRIS wavelength range, from 365 nm to 930 nm,and with full widths at half maximum (FWHM)ranging from 1.2 nm to 4 nm, depending on thewavelength. Both the central wavelength and theFWHM can be tuned in tens of milliseconds. Thesecharacteristics allow performing narrow band tomog-raphy over a wavelength range of interest. In thistechnique, a set of images of the same field is ob-tained at different contiguous wavelengths scanning

1Instituto de Astrofısica de Canarias, La Laguna, Tenerife,Spain (jcn@iac.es).

2Departamento de Astrofısica, Universidad de La Laguna,La Laguna, Tenerife, Spain.

3Australian Astronomical Observatory, Epping NSW, Aus-tralia.

4Instituto de Astrofısica de Andalucıa-CSIC, Granada,Spain.

5Departamento de Astrofısica y C.C. de la Atmosfera, Uni-versidad Complutense de Madrid, Madrid, Spain.

6Instituto de Astronomıa, Universidad Nacional Auto-noma de Mexico, Mexico, D.F., Mexico.

7Instituto de Fısica de Cantabria, CSIC-Universidad deCantabria, Santander, Spain.

8Herschel Science Center (ESAC)/INSA, Madrid, Spain.9Departamento de Fısica, Escuela Superior de Fısica y

Matematica, Instituto Politecnico Nacional, Mexico, D.F.,Mexico.

10Sydney Institute for Astronomy, School of Physics, Uni-versity of Sydney, NSW, Australia.

the desired wavelength interval. Aperture photome-try allows constructing low resolution spectra of thetargets detected in the field, and identifying emis-sion lines. For each emission line, different redshiftranges are mapped. Then, the emission line targetsdetected can range from low redshift galaxies emit-ting in Hα, to Lyman-α emitters at high redshift.The FWHM and the sampling interval drives thespectral resolution and photometric accuracy of the3D spectra, while the exposure time drives the min-imum luminosity detectable at each redshift range.Then, different volumes of universe are scanned atwell defined depths.

OTELO will scan a wavelength interval definedby a window within the OH emission line forest, cen-tered at 920 nm, and spanning 21 nm. The goal is tocover a total area of 0.1 square degrees, distributedin different pointings to the fields GOODS-N, Ex-tended GROTH Strip (EGS), SXDS and selected ar-eas of ACS/COSMOS, to control cosmic statistics. AFWHM of 1.2 nm and a sampling interval of 0.6 nm,allow deblending [NII]λ658.4 nm line from Hα (Lara-Lopez et al. 2011), a feature unique in this type ofsurveys, which is essential for SFR and metallicitydeterminations. Each pointing is observed during108 h, including overheads, with a requested seeingof ≤1 arcsecond.

For the maximum scientific explotation ofOTELO, cross correlation with the ancillary data inthe optical, Near-Infrared (NIR), X-Rays and Far-Infrared will be performed. Optical and NIR al-

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THE OTELO PROJECT 71

Fig. 1. Inverted median image of an OTELO pointing tothe EGS. Encircled galaxies are 2300 sources identifiedin the catalogue of Gwyn (2011), up to magnitud z′23.The field is 7.4×7.1 arcmin2, with a total exposure timeof 85800 s through a “synthetic” 924.4/8.4 nm filter.

low deriving photometric redshifts for identifyingthe emission line of the object detected, and ob-taining morphologies. X-Rays allow identifying Ac-tive Galactic Nuclei (AGN), while 60–200 µm imagesof some OTELO fields obtained with the PACS in-strument on-board Herschel Observatory using guar-anteed time, will allow obtaining complete SEDs,deriving extinction corrected Star Formation Rates(SFR), and correlating extinctions and metallicitieswith FIR luminosities of the different sources de-tected.

The expected follow-ups include optical and NIRMOS of a fraction of the targets at 0.6 < z <

1.5, i.e. those with Hα in the NIR domain and[OII]λ372.7 nm, [OIII]λ500.7 nm in the OTELOspectral window, for SFR and metallicity determi-nations.

2. OTELO IN THE CONTEXT OF OTHEREXTRAGALACTIC SURVEYS

In deep spectroscopic surveys, the sample selec-tion has been done using broad band limited mag-nitude surveys. Then, they are biased to relativelybright continuum targets. OTELO survey is morefocussed to faint continuum, spectroscopically un-reachable targets with emission lines, thus providinga complementary view of the universe.

The most conspicuous emission line survey is thatusing Suprime-Cam in Subaru (see for example Ly etal. 2007). In comparison with this survey, OTELOwill be 2 magnitudes deeper, and will detect equiv-alent widths 10 times narrower. Then, OTELO willdetect most spirals at low redshift, instead of onlythe brightest ones. A fraction of ellipticals in emis-sion will be detected for first time as well. As a sum-mary, OTELO will be the first large-scale emission-line survey fully exploiting the sensitivity and thespectral resolution of tunable filters in a 10 m tele-scope.

3. SCIENTIFIC AIMS

A deep general purpose survey such as OTELOprovides very valuable data for tackling a wide va-riety of projects. Science cases where OTELO willlikely have the greatest impact include: SFR den-sity evolution in the Universe, Lyα emitters, highredshift QSO, AGNs at any redshift, chemical evo-lution of the Universe up to z = 1.5, emission lineellipticals, and galactic emission stars.

The total number of emission line galaxies andits distribution within the different classes is a rele-vant science case on its own, given the present un-certainties in the evolution of the luminosity func-tions. Assuming no evolution and a cosmology withΩM = 0.3, ΩΛ = 0.7, H0 = 65 km s−1 Mpc−1,the total number of emitters in OTELO survey isexpected to be ∼1 × 104, with 77% spirals and el-lipticals up to a redshift 1.5 and 0.84, respectively,18% Seyfert galaxies at z ≤ 1.5, 2% blue compactdwarfs up to z = 0.85, 2.5% Lyα emitters at z up to6.7 (equivalent to 10% of the age of the Universe),and about 0.5% galactic emission stars. Since thelow resolution spectra extracted from the data allowdeblending the Hα from the [NII]λλ654.8,658.4 nmlines, it will be possible estimating the metal con-tents of the targets and a zero-order discriminationbetween the various AGN types.

4. PRELIMINARY RESULTS

So far, only 33% of the first OTELO pointinghas been observed, mostly in photometric conditions,with the last observations obtained recently. A de-tection image obtained by the median of 78 images,synthesizing a 924.4/8.4 nm filter, is shown in Fig-ure 1. The histogram of the flux density of the 2300sources with z′ from Gywn (2011) is shown in Fig-ure 2, indicating that we are achieving a 3σ limitingflux of 5 × 10−19 erg cm−2 s−1, as expected for amean seeing of 0.9± 0.2 arcsec (best seeing 0.64 arc-sec). Figure 3 shows some pseudo-spectra of typical

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72 CEPA ET AL.

Fig. 2. Logarithm of the flux density distribution of the sources detected in the synthetic image of Figure 1.

Fig. 3. Some spectra of typical Hα sources at z ∼ 0.40 obtained adding only 2 exposures (out of 6) at each wavelength.The [NII]λ658.4 nm line can be observed.

galaxies at z ∼ 0.40 obtained adding only 2 out ofthe 6 exposures per wavelength available. The pre-liminary conclusions from the work so far done, indi-cates a lack of faint continuum targets (I(AB)≤23.5)in absorption. Were this confirmed, the current SFRdensity estimations should be revised.

REFERENCES

Gwyn, S. D. J. 2011, arXiv:1101.1084Lara-Lopez, M. A., et al. 2011, PASP, 123, 252Ly, C., et al. 2007, ApJ, 657, 738