Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization

Understand

We report the discovery of Lyman-alpha emission (Ly$\alpha$) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory.

• First reported by Roberts-Borsani et al.
• (2015), it was selected for spectroscopic observations because of its photometric redshift ($z_{phot}=8.57^{+0.22}_{-0.43}$), apparent brightness (H$_{160}=25.26\pm0.09$) and red Spitzer/IRAC [3.6]-[4.5] color indicative of contamination by strong oxygen emission in the [4.5] band.
• With a total integration of $\sim$4.3 hours, our data reveal an emission line at $\simeq$11776 {\AA} which we argue is likely Ly$\alpha$ at a redshift $z_{spec}=8.683^{+0.001}_{-0.004}$, in good agreement with the photometric estimate.