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Reionization-era galaxies tend to exhibit weak Ly$alpha$ emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly$alpha$ emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]$+$H$beta$ emission (EW$>$800 $mathrm{mathring{A}}$). To better understand why Ly$alpha$ is anonymously strong in a subset of massive z$simeq$7$-$9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous ($simeq$1$-$6 L$^{ast}_{mathrm{UV}}$) z$simeq$7 galaxies selected over very wide-area fields ($sim$3 deg$^2$). We confidently ($>$7$sigma$) detect Ly$alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$beta$ emission (EW$>$800 $mathrm{mathring{A}}$) as opposed to only 8% (1/12) of galaxies with more moderate (EW=200$-$800 $mathrm{mathring{A}}$) [OIII]$+$H$beta$. We argue that the higher Ly$alpha$ EWs of the strong [OIII]$+$H$beta$ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs ($gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$alpha$ transmission from massive galaxies declines less rapidly over $6<z<7$ than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly$alpha$ transmission, consistent with a picture wherein massive z$simeq$7 galaxies often reside in large ionized regions. We detect three closely-separated ($R$ = 1.7 physical Mpc) z$simeq$7 Ly$alpha$ emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our ne
We present Gemini/GNIRS spectroscopic observations of 4 z-band (z~7) dropout galaxies and VLT/XSHOOTER observations of one z-band dropout and 3 Y-band (z~8-9) dropout galaxies in the Hubble Ultra Deep Field, which were selected with Wide Field Camera
Ly$alpha$-emitting galaxies (LAEs) are easily detectable in the high-redshift Universe and are potentially efficient tracers of large scale structure at early epochs, as long as their observed properties do not strongly depend on environment. We inve
We quantify the distribution of [OIII]+H$beta$ line strengths at z$simeq$7 using a sample of 20 bright (M$_{mathrm{UV}}$ $lesssim$ $-$21) galaxies. We select these systems over wide-area fields (2.3 deg$^2$ total) using a new colour-selection which p
We present diffuse Lyman-alpha halos (LAHs) identified in the composite Subaru narrowband images of 100-3600 Lyman-alpha emitters (LAEs) at z=2.2, 3.1, 3.7, 5.7, and 6.6. First, we carefully examine potential artifacts mimicking LAHs that include a l