UBIQUITOUS GIANT Lyα NEBULAE AROUND THE BRIGHTEST QUASARS AT z ∼ 3.5 REVEALED WITH MUSE

Direct Ly alpha imaging of intergalactic gas at z similar to 2 has recently revealed giant cosmological structures around quasars, e.g., the Slug Nebula. Despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. In this study, we use the MUSE integral-field instrument to perform a blind survey for giant Ly alpha nebulae around 17 bright radio-quiet quasars at 3 < z < 4 that does not suffer from most of the limitations of previous surveys. After data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant Ly alpha nebulae with projected sizes larger than 100 physical kiloparsecs and, in some cases, extending up to 320 kpc. The circularly averaged surface brightness profiles of the nebulae appear to be very similar to each other despite their different morphologies and are consistent with power laws with slopes. approximate to-1.8. The similarity between the properties of all these nebulae and the Slug Nebula suggests a similar origin for all systems and that a large fraction of gas around bright quasars could be in a relatively "cold" (T similar to 10(4) K) and dense phase. In addition, our results imply that such gas is ubiquitous within at least 50 kpc from bright quasars at 3 < z < 4 independently of the quasar emission opening angle, or extending up to 200 kpc for quasar isotropic emission.