Hubble Space Telescope Narrowband Search for Extended Lyα Emission around Two z > 6 Quasars

Abstract

We search for extended Lyα emission around two z > 6 quasars, SDSS J1030+0524 (z = 6.309) and SDSS J1148+5251 (z = 6.419) using Wide Field Camera 3 narrowband filters on board the Hubble Space Telescope. For each quasar, we collected two deep, narrowband images, one sampling the Lyα line+continuum at the quasar redshifts and one of the continuum emission redward of the line. After carefully modeling the point-spread function, we find no evidence for extended Lyα emission. These observations set 2σ limits of L(Lyα, extended) <3.2 × 10^(44) erg s^(–1) for J1030+0524 and L(Lyα, extended) <2.5 × 10^(44) erg s^(–1) 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 Lyα emission expected from the recombination of gas photoionized by the quasars or by the star formation in the host galaxies, and point toward significant Lyα 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 Lyα suppression (e.g., resonance scattering). No Lyα emitting companions are found, down to a 5σ sensitivity of ~1 × 10^(–17) erg s^(–1) cm^(–2) arcsec^(–2) (surface brightness) and ~5 × 10^(–17) erg s^(–1) cm^(–2) (assuming point sources).

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