First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ∼ 7
Abstract
We present the first results from the ongoing Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) project, which is the largest narrowband survey for z ∼ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark Energy Camera (DECam) on the NOAO/CTIO 4 m Blanco telescope, LAGER has collected 34 hr NB964 narrowband imaging data in the 3 deg2 COSMOS field. We have identified 23 Lyα Emitter candidates at z = 6.9 in the central 2-deg2 region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function (LF) can be described as a Schechter function modified by a significant excess at the bright end (four galaxies with L Lyα ∼ 1043.4±0.2 erg s-1). The number density at L Lyα ∼ 1043.4±0.2 erg s-1 is little changed from z = 6.6, while at fainter L Lyα it is substantially reduced. Overall, we see a fourfold reduction in Lyα luminosity density from z = 5.7 to z = 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of ∼3 suppression of Lyα by radiative transfer through the z ∼ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction of x H I ∼ 0.4-0.6 (assuming Lyα velocity offsets of 100-200 km s-1). The changing shape of the Lyα LF between z ≲ 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z ∼ 7.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2017
- DOI:
- arXiv:
- arXiv:1703.02985
- Bibcode:
- 2017ApJ...842L..22Z
- Keywords:
-
- cosmology: observations;
- dark ages;
- reionization;
- first stars;
- galaxies: high-redshift;
- galaxies: luminosity function;
- mass function;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 7 pages, 3 figures (updated), 2 tables (updated), Accepted for publication in ApJ Letters