Spectroscopic Observation of Lyα Emitters at z ~ 7.7 and Implications on Re-ionization

June 2014 • 2014ApJ...788...87F

Authors • Faisst, A. L. • Capak, P. • Carollo, C. M. • Scarlata, C. • Scoville, N.

Abstract • We present spectroscopic follow-up observations on two bright Lyα emitter (LAE) candidates originally found by Krug et al. at a redshift of z ~ 7.7 using the Multi-Object Spectrometer for Infra-Red Exploration at Keck. We rule out any line emission at the >5σ level for both objects, putting on solid ground a previous null result for one of the objects. The limits inferred from the non-detections rule out the previous claim of no or even reversed evolution between 5.7 < z < 7.7 in the Lyα luminosity function (LF) and suggest a drop in the Lyα LF consistent with that seen in Lyman break galaxy (LBG) samples. We model the redshift evolution of the LAE LF using the LBG UV-continuum LF and the observed rest-frame equivalent width distribution. From the comparison of our empirical model with the observed LAE distribution, we estimate lower limits of the neutral hydrogen fraction to be 50%-70% at z ~ 7.7. Together with this, we find a strong evolution in the Lyα optical depth characterized by (1 + z)2.2 ± 0.5 beyond z = 6, indicative of a strong evolution of the intergalactic medium. Finally, we extrapolate the LAE LF to z ~ 9 using our model and show that it is unlikely that large area surveys, like UltraVISTA or Euclid, pick up LAEs at this redshift assuming the current depths and area.


IPAC Authors


Andreas Faisst

Assistant Scientist