The current galaxy formation paradigm postulates that a significant amount of gas accretes onto galaxies from the IGM in a cold T ~ 104K phase, and many have argued that this gas should be detectable in diffuse Lyα emission. However, so far, there are no convincing direct detections.
We are conducting a deep (down to 1σ ~ 5 − 10 × 10−19 erg s−1 cm−2 arcsec−2) and the first statistical survey matching the Lyα line around radio-quiet quasars at z ~ 2. By taking advantage of the boost in fluorescent Lyα emission due to the ionizing radiation emitted by a luminous QSO that, like a flashlight, can illuminate the hydrogen in its vicinity, we will be able to constrain some of the properties of the gas sorrounding z ~ 2 QSOs. In particular, with this unique dataset, we can conduct the first deep statistical census of the size, morphology, luminosity, frequency, and covering factor of Lyα emission around QSOs.