Abstract
We present the first results from the ongoing LAGER project (Lyman Alpha
Galaxies in the Epoch of Reionization), which is the largest narrowband survey
for $z\sim$ 7 galaxies to date. Using a specially built narrowband filter NB964
for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco
telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3
deg$^2$ COSMOS field. We have identified 27 Lyman Alpha Emitter (LAE)
candidates at $z=$ 6.9 in the central 2-deg$^2$ region, where DECam and public
COSMOS multi-band images exist. The resulting luminosity function can be
described as a Schechter function modified by a significant excess at the
bright end (4 galaxies with L$_Ly\alpha\sim$ 10$^43.4\pm0.2$ erg s$^-1$).
The number density at L$_Ly\alpha\sim$ 10$^43.4\pm0.2$ erg s$^-1$ is
little changed from $z= 6.6$, while at fainter $L_Ly\alpha$ it is
substantially reduced. Overall, we see a fourfold reduction in Ly$\alpha$
luminosity density from $z= 5.7$ to $6.9$. Combined with a more modest
evolution of the continuum UV luminosity density, this suggests a factor of
$3$ suppression of Ly$\alpha$ by radiative transfer through the $z7$
intergalactic medium (IGM). It indicates an IGM neutral fraction $x_HI$
$\sim$ 0.4-0.6 (assuming Ly$\alpha$ velocity offsets of 100-200 km s$^-1$).
The changing shape of the Ly$\alpha$ luminosity function between $złesssim
6.6$ and $z=6.9$ supports the hypothesis of ionized bubbles in a patchy
reionization at $z\sim$ 7.
Users
Please
log in to take part in the discussion (add own reviews or comments).