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 Lyα emission (possibly accompanied by other lines), detectable as a “fuzz” of characteristic angular diameter of a few arcseconds, and surface brightness ∼> 10 −18 erg s cm asec. From the apparent paucity of such Lyα halos, we infer that most of the protogalaxy’s gas must settle to a self– gravitating disk before a quasar turns on, or else that an intense outflow from the quasar quickly blows out the surrounding gas. Continued infall of gas 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 significant extended Lyα emission, and can be constrained by deep narrow band imaging. Subject headings: cosmology: theory – galaxies: formation – quasars: general – black hole physics