New Observations of Z~7 Galaxies: Evidence for a Patch Reionization

We present new results from our search for z∼ 7 galaxies from deep spectroscopic observations of candidate z-dropouts in the CANDELS fields. Despite the extremely low flux limits achieved by our sensitive observations, only 2 galaxies have robust redshift identifications, one from its Lyα emission line at z=6.65, the other from its Lyman-break, i.e. the continuum discontinuity at the Lyα wavelength consistent with a redshift 6.42, but with no emission line. In addition, for 23 galaxies we present deep limits in the Lyα EW derived from the non detections in ultra-deep observations. Using this new data as well as previous samples, we assemble a total of 68 candidate z∼ 7 galaxies with deep spectroscopic observations, of which 12 have a line detection. With this much enlarged sample we can place solid constraints on the declining fraction of Lyα emission in z∼7 Lyman break galaxies compared to z∼ 6, both for bright and faint galaxies. Applying a simple analytical model, we show that the present data favor a patchy reionization process rather than a smooth one