ODIN: Spectroscopic Validation of Ly$\alpha$-Emitting Galaxy Samples with DESI

TL;DR

The ODIN survey uses narrow-band imaging combined with DESI spectroscopy to validate and confirm high-redshift Lyman-alpha emitting galaxy samples with high accuracy and minimal contamination.

Contribution

This work provides the first spectroscopic validation of ODIN's narrow-band selected LAE samples across multiple redshifts, demonstrating high confirmation rates and effective contamination control.

Findings

High confirmation rates of 92-96% for ODIN LAE candidates.

Minimal contamination from low-redshift emitters (<1%).

Effective use of narrow-band excess criteria to select LAEs.

Abstract

The One-hundred-deg^2 DECam Imaging in Narrowbands (ODIN) survey is conducting the widest-field deep narrow-band imaging of the equatorial and southern skies. ODIN uses three custom-built narrow-band (NB) filters that sample Lya-emitting galaxies (LAEs) within thin cosmic slices centered at z=2.4, 3.1, and 4.5. In this work, we utilize extensive DESI spectroscopy of ODIN-selected galaxies in the COSMOS and XMM-LSS fields to validate our LAE selection. 2-4 hr exposures with DESI yielded redshift confirmation of 3,075 ODIN LAE candidates with NB magnitudes brighter than 26~mag. Restricting to objects that yield high-confidence redshifts, the confirmation rates are (93, 96, 92)% at z=(2.4, 3.1, 4.5). The primary contaminants consist of active galactic nuclei at the expected Lya redshift range and lower redshifts (C IV, C III]), with the remainder being star-forming galaxies ([O II] and [O III]). We find minimal contamination from [O II] emitters in our sample (<~1%), implying that our REW>20 A narrow-band excess photometry requirement is sufficient to remove them.