The Magellan M2FS Spectroscopic Survey of High-$z$ Galaxies: Lyα Emitters at $zapprox6.6$ and the Evolution of Lyα Luminosity Function over $zapprox5.7-6.6$

Kavli Affiliate: Linhua Jiang

| First 5 Authors: Yuanhang Ning, Linhua Jiang, Zhen-Ya Zheng, Jin Wu,

| Summary:

We present a sample of Ly{alpha} emitters (LAEs) at $zapprox6.6$ from our
spectroscopic survey of high-redshift galaxies using the multi-object
spectrograph M2FS on the Magellan Clay telescope. The sample consists of 36
LAEs selected by the narrow-band (NB921) technique over nearly 2 deg$^2$ in the
sky. These galaxies generally have high Ly{alpha} luminosities spanning a
range of ${sim}3times10^{42}{-}7times10^{43}$ erg s$^{-1}$, and include some
of the most Ly{alpha}-luminous galaxies known at this redshift. They show a
positive correlation between the Ly{alpha} line width and Ly{alpha}
luminosity, similar to the relation previously found in $zapprox5.7$ LAEs.
Based on the spectroscopic sample, we calculate a sophisticated sample
completeness correction and derive the Ly{alpha} luminosity function (LF) at
$zapprox6.6$. We detect a density bump at the bright end of the Ly{alpha} LF
that is significantly above the best-fit Schechter function, suggesting that
very luminous galaxies tend to reside in overdense regions that have formed
large ionized bubbles around them. By comparing with the $zapprox5.7$
Ly{alpha} LF, we confirm that there is a rapid LF evolution at the faint end,
but a lack of evolution at the bright end. The fraction of the neutral hydrogen
in the intergalactic medium at $zapprox6.6$ estimated from such a rapid
evolution is about $sim0.3pm0.1$, supporting a rapid and rather late process
of cosmic reionization.

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