NEW OBSERVATIONS OFz∼ 7 GALAXIES: EVIDENCE FOR A PATCHY REIONIZATION

Abstract

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.

The Galaxy UV Luminosity Function Before the Epoch of Reionization

“…Qualitatively, the non-negligible neutral fraction predicted by our model at z ∼ > 7 is consistent with the observed high optical depth of Lyα (Ouchi et al 2010;Treu et al 2013;Pentericci et al 2014;Schenker et al 2014;Tilvi et al 2014;Faisst et al 2014, K. B. Schmidt et al 2015, ApJ submitted), however the conversion from the Lyα emission fraction to the volume filling factor of ionized hydrogen is difficult and requires several assumptions . In particular, to make constraints on reionization it is generally assumed that there are no changes in galaxy and the Lyα emission line properties, which necessitates a rapid evolution of the global ionization fraction between z ∼ 6 and z ∼ 7.…”

“…We plot our results from integrating the model UV LFs to two magnitude limits of Mab = −17 (green) and Mab = −12 (purple), with 1σ confidence regions as shaded regions. We also plot constraints derived from observations of: Lyα emission from galaxies (open circles, Ouchi et al 2010;Pentericci et al 2014;Tilvi et al 2014;Faisst et al 2014;Schenker et al 2014); the Lyα forest (filled circles, Fan et al 2006); the clustering of Lyα emitting galaxies (square, Ouchi et al 2010); GRB spectra damping wings (diamond, McQuinn et al 2008); dark gaps in the Lyα forest (upper triangles, McGreer et al 2015); quasar near zones (star, Venemans et al 2015); and quasar spectra damping wings (lower triangle, Schroeder et al 2013). We also plot the Planck Collaboration et al (2015) redshift of instantaneous reionization.…”

Characterization of star-forming dwarf galaxies at 0.1 ≲z ≲ 0.9 in VUDS: probing the low-mass end of the mass-metallicity relation

“…Large efforts are currently being invested to identify the first luminous sources which reionized the neutral intergalactic medium at redshifts higher than 6 (e.g., Pentericci et al 2014;Robertson et al 2015;Giallongo et al 2015;Grazian et al 2016). One of the main contributors to cosmic reionization are faint SFDGs with a significant fraction of escaping Lyman continuum photons (i.e., emission at wavelengths λ < 912 Å).…”

The Impact of JWST Broadband Filter Choice on Photometric Redshift Estimation

“…We Redshift distribution of the three galaxy samples considered in this work: a galaxy sample with spectroscopic redshifts in the GOODS-S field (filled gray; sample 1), a galaxy sample with well-established CANDELS photometric redshifts, also in GOODS-S (red line; sample 2), and a sample of simulated galaxies with known input redshifts (dashed line; sample 3). explicitly decided not to include the Lyα line because the importance of its emission in galaxies at > z 7 is still unclear (e.g., Stark et al 2013;Konno et al 2014;Pentericci et al 2014). Finally, we normalized every model at 29AB mag at 1.5 μm (corresponding to the NIRCam F150W filter pivot wavelength).…”