(Proposal ID) S10B-045

(PI) Takada, Masahiro

(Proposal Title)
Subaru weak lensing observations of ACT SZ-selected galaxy clusters

(Abstract)
The abundance of massive clusters as a function of redshift is a very powerful 
probe of cosmology, including the equation of state of dark energy, when 
combined with precise constraints on the initial conditions of structure 
formation from WMAP. The Sunyaev-Zel'dovich (SZ) effect, which is independent 
of redshift, offers a unique means of finding clusters up to high redshifts. 
However, systematic SZ surveys of cosmological volumes are currently in their 
infancy, and require crosscalibration with weak gravitational lensing to 
determine the relationship between SZ observables and mass. We request one 
night for a multi-band observation with Suprime-Cam of the two most SZ 
luminous clusters (previously unknown) in ~ 200 sq. deg. of early data from 
the equatorial region of the Atacama Cosmology Telescope (ACT) survey, with 
estimated masses of 10^15h^-1M_sun at redshifts z = 0.46 and 0.81. To obtain 
unbiased lensing signals, multi-band imaging is needed so that a pure catalog 
of background galaxies can be identified via photometric redshifts. This 
observation will allow for a determination of the masses to within 10-20%, and 
is the first step in enabling precision cosmology with SZ-selected cluster 
samples, eventually done in combination with the Hyper Suprime-Cam Survey.