Mass - to - light Ratio of Ly α Emitters : Implications of Ly α Surveys at Redshifts z = 5 .

Using a simple method to interpret the luminosity function of Lyα emitters, we explore properties of Lyα emitters from 5.7 6 z 6 8.8 with various assumptions about metallicity and stellar mass spectra. We constrain a mass-to-“observed light” ratio, Mh/Lband, where Mh refers to the total mass of the host halo, and Lband refers to the observed luminosity of the source. For narrow-band surveys, Lband is simply related to the intrinsic Lyα luminosity with a survival fraction of Lyα photons, αesc. The massto-“bolometric light”, Mh/Lbol, can also be deduced, once the metallicity and stellar mass spectrum are given. The inferred Mh/Lbol is more sensitive to metallicity than to the mass spectrum. We find the following constraints on a mass-to-light ratio of Lyα emitters from 5.7 6 z 6 7: (Mh/Lbol)(αescǫ ) = 21− 38, 14− 26, and 9 − 17 for Z = 0, 1/50, and 1 Z⊙, respectively, where ǫ is the “duty cycle” of Lyα emitters, and γ ∼ 2 is a local slope of the cumulative luminosity function, N(> L) ∝ L , to which the current data are sensitive. Only weak lower limits are obtained for z = 8.8. Therefore, Lyα emitters are consistent with either starburst galaxies (Mh/Lbol ∼ 0.1 − 1) with a smaller Lyα survival fraction, αescǫ 1/γ ∼ 0.01 − 0.05, or normal populations (Mh/Lbol ∼ 10) if a good fraction of Lyα photons survived, αescǫ 1/γ ∼ 0.5 − 1. We find no evidence for the end of reionization in the luminosity functions of Lyα emitters discovered in the current Lyα surveys, including recent discovery of one Lyα emitter at z = 7. The data are consistent with no evolution of intrinsic properties of Lyα emitters or neutral fraction in the intergalactic medium up to z = 7. No detection of sources at z = 8.8 does not yield a significant constraint yet. We also show that the lack of detection at z = 8.8 does not rule out the high-z galaxies being the origin of the excess near infrared background.