Probing Cosmology with Weak Lensing Peak Counts
  We propose counting peaks in weak lensing (WL) maps, as a function of their
height, to probe models of dark energy and to constrain cosmological
parameters. Because peaks can be identified in two-dimensional WL maps
directly, they can provide constraints that are free from potential selection
effects and biases involved in identifying and determining the masses of galaxy
clusters. We have run cosmological N-body simulations to produce WL convergence
maps in three models with different constant values of the dark energy equation
of state parameter, w=-0.8, -1, and -1.2, with a fixed normalization of the
primordial power spectrum (corresponding to present-day normalizations of
sigma8=0.742, 0.798, and 0.839, respectively). By comparing the number of WL
peaks in 8 convergence bins in the range of -0.1 < kappa < 0.2, in multiple
realizations of a single simulated 3x3 degree field, we show that the first
(last) pair of models can be distinguished at the 95% (85%) confidence level. A
survey with depth and area (20,000 sq. degrees), comparable to those expected
from LSST, should have a factor of approx. 50 better parameter sensitivity. We
find that relatively low-amplitude peaks (kappa = 0.03), which typically do not
correspond to a single collapsed halo along the line of sight, account for most
of this sensitivity. We study a range of smoothing scales and source galaxy
redshifts (z_s). With a fixed source galaxy density of 15/arcmin^2, the best
results are provided by the smallest scale we can reliably simulate, 1
arcminute, and z_s=2 provides substantially better sensitivity than z_s< 1.5.
