Galaxies inside Strmgren Spheres of Luminous Quasars at z >6: Detection of the First Galaxies

The intrinsic Lyman-alpha emission lines of normal galaxies beforereionization are much absorbed by the damping wing of the Gunn-Peterson trough,rendering their direct detection nearly impossible, if their intrinsic linewidths are less than ~100km/s. High redshift luminous quasars prior to thecompletion of cosmological reionization at z~6, on the other hand, are capableof producing large HII regions around them (Stromgren spheres) to allow theirintrinsic Lyman-alpha emission lines to be transmitted without overwhelmingabsorption (Cen & Haiman 2000). We suggest that targeted observations at theStromgren spheres of known luminous quasars at z >= 6 would be able to detectLyman-alpha emission lines of galaxies inside the Stromgren spheres largelyunattenuated. A tunable, very narrowband filter of \Delta\lambda\over \lambda ~0.1% or a narrowband filter of \Delta\lambda\over \lambda ~1% with follow-upspectroscopic identifications will be required. Such observations coulddirectly observe the sources of cosmological reionization including possiblythe Pop III galaxies at z=6-20 by JWST. Possible applications includedeterminations of the ionization state of the intergalactic medium, the sizesof the Stromgren spheres, the ages of the quasars, the luminosity function ofhigh redshift galaxies and its evolution, the spatial distribution of galaxiesand its evolution, the biased distribution of galaxies around quasars and theanisotropy of quasar emission. Observations using Keck-class telescopes mayalready be made to enable a differentiation between a fully neutral and a 10%neutral intergalactic medium at z>6.Comment: Submitted to ApJ Letters, 10 page