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HST narrow-band search for extended Ly-alpha emission around two z>6 quasars

We search for extended Ly-alpha emission around two z>6 quasars, SDSS J1030+0524 (z=6.309) and SDSS J1148+5251 (z=6.419) using WFC3 narrow-band filters on board the Hubble Space Telescope. For each quasar, we collected two deep, narrow-band images, one sampling the Ly-alpha line+continuum at the quasar redshifts and one of the continuum emission redwards of the line. After carefully modeling the Point Spread Function, we find no evidence for extended Ly-alpha emission. These observations set 2-sigma limits of L(Ly-alpha, extended) < 3.2 x 10^{44} erg/s for J1030+0524 and L(Ly-alpha, extended) < 2.5 x 10^{44} erg/s for J1148+5251. Given the star formation rates typically inferred from (rest-frame) far-infrared measurements of z~6 quasars, these limits are well below the intrinsic bright Ly-alpha emission expected from the recombination of gas photoionized by the quasars or by the star formation in the host galaxies, and point towards significant Ly-alpha suppression or dust attenuation. However, small extinction values have been observed along the line of sight to the nuclei, thus reddening has to be coupled with other mechanisms for Ly-alpha suppression (e.g., resonance scattering). No Ly-alpha emitting companions are found, down to a 5-sigma sensitivity of ~ 1 x 10^{-17} erg/s/cm^2/arcsec^2 (surface brightness) and ~ 5 x 10^{-17} erg/s/cm^2 (assuming point sources).