(Proposal ID) S17B-005

(PI) Mawatari, Ken

(Proposal Title)
Panoramic H_I mapping in the z = 3.1 supercluster with HSC

(Abstract)
This proposal aims to map the neutral hydrogen (H_I) gas in/around the SSA22 
supercluster at z=3.1 in an unprecedented large-scale of > 200 comoving Mpc 
(cMpc). We have developed an innovative method for mapping the H_I distribution
 by using narrowband NB497 imaging data and showed that the H_I gas structure 
in the SSA22 supercluster spreads out more than 50 cMpc (Mawatari et al. 2017).
The survey area in this pilot study was limited by the distribution of 
background light sources whose NB497 photometry contains the z = 3.1 H_I 
information. We needed galaxies spectroscopically confirmed to be at z ~ 3.4 
as the secure background sources. However, we have NB497 and broadband images 
covering a much wider area. Here we propose HSC NB527 observations to collect 
continuum-bright Lyalpha emitters (LAEs) at z=3.33 as the background light 
sources. Only ~1 hour on-source exposure with the HSC NB527 allows us to 
select LAEs with NB527 < 25 and r < 26. Their expected mean separation is 
~5 arcmin, leading an H_I mapping resolution of ~10 cMpc at z = 3.1. We will 
also observe the SXDS field, where wide-area NB497 and broadband images are 
also available, as a control field. We request on-source 3 hours for 3 
pointings toward the two target fields.