(Proposal ID) S17A-136 (PI) Momose, Rieko (Proposal Title) Large-scale intensity mapping of Ly alpha emission around 7 QSOs at z=2.2 (Abstract) We propose deep and large-scale Ly alpha intensity mapping around 7 QSOs at z=2.2 with the NB387 filter of HSC to confirm the presence of the large-scale Ly alpha emission in the CGM and IGM, and clarify the major contributor to them. Recently, Croft et al. (2016) have found the large-scale Ly alpha emission in the IGM at z=2-3.5 by measuring the QSO-Ly alpha emission cross- correlation using SDSS/BOSS spectra. Though this discovery is crucial to understand the galaxy evolution, the presence of large-scale Ly alpha emission itself and the contributors of the emission are still under debate. In order to conclude these arguments, we investigate the diffuse Ly alpha surface brightness as a function of distance from a QSO by taking advantage of wide field of view of HSC. Combining the results of diffuse Ly alpha emitting haloes around Ly alpha emitters from our previous studies (Momose et al. 2014, 2016) and coming u*-band data of MegaCam/CFHT, we will elucidate which of the sources, QSOs or star-forming galaxies, contribute to the large-scale Ly alpha emission. Our HSC observations will be able to detect the large-scale Ly alpha emission in the IGM at 5 sigma level with 20.3 hours of dark nights, and conclude the presence and origin of diffuse Ly alpha emission in the IGM.