Research Note

Measuring galaxy [O ii] emission line doublet with future ground-based wide-field spectroscopic surveys

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: johan.comparat@lam.fr
² Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
³ CRAL, Observatoire de Lyon, Université Lyon 1, 9 avenue Ch. André, 69561 Saint-Genis-Laval Cedex, France
⁴ Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
⁵ Department of Physics and Astronomy, University of Pittsburgh and PITT-PACC, 3941 O’Hara St., Pittsburgh, PA 15260, USA
⁶ CEA, Centre de Saclay, IRFU, 91191 Gif-sur-Yvette, France

Received: 6 August 2013
Accepted: 20 September 2013

Abstract

The next generation of wide-field spectroscopic redshift surveys will map the large-scale galaxy distribution in the redshift range 0.7 ≤ z ≤ 2 to measure baryonic acoustic oscillations (BAO). The primary optical signature used in this redshift range comes from the [Oii] emission line doublet, which provides a unique redshift identification that can minimize confusion with other single emission lines. To derive the required spectrograph resolution for these redshift surveys, we simulate observations of the [Oii] (λλ 3727, 3729) doublet for various instrument resolutions, and line velocities. We foresee two strategies for the choice of the resolution for future spectrographs for BAO surveys. For bright [Oii] emitter surveys ([Oii] flux ~30 × 10^-17  erg   cm^-2   s^-1 like SDSS-IV/eBOSS), a resolution of R ~ 3300 allows the separation of 90 percent of the doublets. The impact of the sky lines on the completeness in redshift is less than 6 percent. For faint [Oii] emitter surveys ([Oii] flux ~10 × 10^-17  erg   cm^-2   s^-1 like DESi), the detection improves continuously with resolution, so we recommend the highest possible resolution, the limit being given by the number of pixels (4k by 4k) on the detector and the number of spectroscopic channels (2 or 3).