The Luminosity Function of Lyman alpha Emitters at Redshift z=7.7

TL;DR

This study conducted a narrowband imaging survey at z=7.7 to detect Lyman alpha emitters, providing insights into the epoch of reionization and demonstrating the feasibility of near-infrared narrow-band searches.

Contribution

First ultra-narrowband imaging survey at z=7.7 for Lyman alpha emitters, showing potential to probe reionization and the evolution of the luminosity function.

Findings

Detected four candidate Lyman alpha emitters at z=7.7

Expected to detect one emitter assuming no evolution in LF from z=6.5 to 7.7

Results suggest possible stability of Lya luminosity function over this redshift range

Abstract

Lyman alpha (Lya) emission lines should be attenuated in a neutral intergalactic medium (IGM). Therefore the visibility of Lya emitters at high redshifts can serve as a valuable probe of reionization at about the 50% level. We present an imaging search for z=7.7 Lya emitting galaxies using an ultra-narrowband filter (filter width= 9A) on the NEWFIRM imager at the Kitt Peak National Observatory. We found four candidate Lya emitters in a survey volume of 1.4 x 10^4 Mpc^3, with a line flux brighter than 6x10^-18 erg/cm^2/s (5 sigma in 2" aperture). We also performed a detailed Monte-Carlo simulation incorporating the instrumental effects to estimate the expected number of Lya emitters in our survey, and found that we should expect to detect one Lya emitter, assuming a non-evolving Lya luminosity function (LF) between z=6.5 and z=7.7. Even if one of the present candidates is spectroscopically confirmed as a z~8 Lya emitter, it would indicate that there is no significant evolution of the Lya LF from z=3.1 to z~8. While firm conclusions would need both spectroscopic confirmations and larger surveys to boost the number counts of galaxies, we successfully demonstrate the feasibility of sensitive near-infrared (1.06 um) narrow-band searches using custom filters designed to avoid the OH emission lines that make up most of the sky background.