Mass-to-light ratio of Lyα emitters: implications of Lyα surveys at redshifts z= 5.7, 6.5, 7 and 8.8

ABSTRACT

Using a simple method to interpret the luminosity function of Lyα emitters, we explore properties of Lyα emitters from 5.7 ≤z≤ 8.8 with various assumptions about metallicity and stellar mass spectra. We constrain a mass-to-'observed light' ratio, M_h/L_band, where M_h refers to the total mass of the host halo and L_band refers to the observed luminosity of the source. For narrow-band surveys, L_band is simply related to the intrinsic Lyα luminosity with a survival fraction of Lyα photons, α_esc. The mass-to-'bolometric light', M_h/L_bol, can also be deduced, once the metallicity and stellar mass spectrum are given. The inferred M_h/L_bol 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 ≤z≤ 7:  (M_h/L_bol)(α_escε^1/γ)⁻¹= 21–38, 14–26  and 9–17 for  Z= 0 , 1/50 and  1 Z_⊙ , respectively, where ε is the 'duty cycle' of Lyα emitters and γ∼ 2 is a local slope of the cumulative luminosity function, N(>L) ∝L^−γ, 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 (M_h/L_bol∼ 0.1–1) with a smaller Lyα survival fraction, α_escε^1/γ∼ 0.01–0.05, or normal populations (M_h/L_bol∼ 10) if a good fraction of Lyα photons survived, α_escε^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.