Extended Lyα emission around young quasars:: A constraint on galaxy formation

The early stage in the formation of a galaxy inevitably involves a spatially extended distribution of infalling, cold gas. If a central luminous quasar turned on during this phase, it would result in significant extended Ly alpha emission, possibly accompanied by other lines. For halos condensing at redshifts 3 less than or similar to z less than or similar to 8 and having virial temperatures 2 x 10(5) K less than or similar to T-vir less than or similar to 2 x 10(6) K, this emission results in a "fuz" of characteristic angular diameter of a few arcseconds and surface brightness similar to 10(-18) to 10(-16) ergs s(-1) cm(-2) arcsec(-2). The fuzz around bright, high-redshift quasars could be detected in deep narrowband imaging with current telescopes, providing a direct constraint on galaxy formation models. The absence of detectable fuzz might suggest that most of the protogalaxy's gas settles to a self-gravitating disk before a quasar turns on. However, continued gas infall from large radii, or an on-going merger spreading cold gas over a large solid angle, during the luminous quasar phase could also result in extended Ly alpha emission, and can be constrained by deep narrowband imaging.