First spectroscopic measurements of [OIII] emission from Lyman-alpha selected field galaxies at z ~ 3.1

TL;DR

This study reports the first spectroscopic detection of [OIII] emission in z~3.1 Lyman-alpha galaxies, revealing velocity offsets indicative of outflows and providing new constraints on their physical properties.

Contribution

It presents the first direct measurements of [OIII] lines in high-redshift LAEs, improving understanding of their systemic velocities and physical characteristics.

Findings

Velocity offsets between [OIII] and Ly-alpha lines indicate powerful outflows.

[OIII] lines are strong enough to affect broad-band photometry and derived galaxy properties.

Provides constraints on the strength of [OIII] emission in high-redshift LAEs.

Abstract

We present the first spectroscopic measurements of the [OIII] 5007 A line in two z ~ 3.1 Lyman-alpha emitting galaxies (LAEs) using the new near-infrared instrument LUCIFER1 on the 8.4m Large Binocular Telescope (LBT). We also describe the optical imaging and spectroscopic observations used to identify these Lya emitting galaxies. Using the [OIII] line we have measured accurate systemic redshifts for these two galaxies, and discovered a velocity offset between the [OIII] and Ly-alpha lines in both, with the Lya line peaking 342 and 125 km/s redward of the systemic velocity. These velocity offsets imply that there are powerful outflows in high-redshift LAEs. They also ease the transmission of Lya photons through the interstellar medium and intergalactic medium around the galaxies. By measuring these offsets directly, we can refine both Lya-based tests for reionization, and Lya luminosity function measurements where the Lya forest affects the blue wing of the line. Our work also provides the first direct constraints on the strength of the [OIII] line in high-redshift LAEs. We find [OIII] fluxes of 7 and 36 x 10^-17 erg s^-1 cm^-2 in two z ~ 3.1 LAEs. These lines are strong enough to dominate broad-band flux measurements that include the line (in thiscase, K_s band photometry). Spectral energy distribution fits that do not account for the lines would therefore overestimate the 4000 A (and/or Balmer) break strength in such galaxies, and hence also the ages and stellar masses of such high-z galaxies.