Extended Lyman Alpha Emission Around Young Quasars: a Constraint on Galaxy Formation

Abstract

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 Lyman alpha emission, possibly accompanied by other lines. For halos condensing at redshifts between 3 < z < 8 and having virial temperatures between 2 x 10^5 K and 2 x 10^6 K, this emission results in a ``fuzz'' of characteristic angular diameter of a few arcseconds, and surface brightness between 10^-18 and 10^-16 erg/s/cm^2/asec^2. The fuzz around bright, high redshift quasars could be detected in deep narrow band imaging with current telescopes, providing a direct constraint on galaxy formation models. The absence of detectable fuzz might suggest that most 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 narrow band imaging.