This collection of three SNAP weak lensing papers
summarise the effectiveness of SNAP as a tool for weak lensing
measurements; estimate it's sensitivity; and perform trade-off studies to
optimise survey strategy for measurements of dark energy.
Weak Lensing from Space I: Prospects for the Supernova Acceleration Probe Authors:Jason Rhodes, Alexandre Refregier, Richard Massey, Justin
Albert, David Bacon, Gary Bernstein, Richard Ellis, Alex Kim, Mike Lampton,
Tim McKay, C. Akerlof, G. Aldering, R. Amanullah, P. Astier, E. Barrelet, C.
Bebek, L. Bergstrom, J. Bercovitz, M. Bester, A. Bonissent, C. Bower, W.
Carithers, E. Commins, C. Day, S. Deustua, R. DiGennaro, A. Ealet, M.
Eriksson, A. Fruchter, J-F. Genat, G. Goldhaber, A. Goobar, D. Groom, S.
Harris, P. Harvey, H. Heetderks, S. Holland, D. Huterer, A. Karcher, W. Kolbe,
B. Krieger, R. Lafever, J. Lamoureux, M. Levi, D. Levin, E. Linder, S. Loken,
R. Malina, S. McKee, R. Miquel, E. Mortsell, N. Mostek, S. Mufson, J. Musser,
P. Nugent, H. Oluseyi, R. Pain, N. Palaio, D. Pankow, S. Perlmutter, R. Pratt,
E. Prieto, K. Robinson, N. Roe, M. Sholl, M. Schubnell, G. Smadja, G. Smoot,
A. Spadafora, G. Tarle, A. Tomasch, H. von der Lippe, D. Vincent, J-P. Walder &
Abstract: The proposed Supernova/Acceleration Probe (SNAP) satellite has been recognized
as an ideal instrument to measure the accelerating expansion of the Universe
through the distance moduli to type Ia supernovae. We show that SNAP will
also be excellent for surveys of weak gravitational lensing by large-scale
structure. Many of the requirements for precise photometry are compatible with
those to accurately measure the shapes of background galaxies. We describe two
surveys to be performed by SNAP. A 15 square degree deep survey will find
clusters/groups and allow two- and three-dimensional dark matter maps to be
made. A 300 square degree wide survey will be used to provide global
constraints on cosmological parameters including Omega_m and w, the dark
energy equation of state. Both surveys will be conducted in 9 wide-band
optical and near-IR filters, enabling photometric redshifts to be calculated.
This first paper in a three part series outlines the survey strategies and
introduces the SNAP instrument in the context of weak lensing. We discuss
relevant systematic effects, particularly the telescope's point spread
function (PSF). We show that SNAP's PSF will be smaller than current
ground-based PSFs, and more isotropic and stable over time than the PSF of the
Hubble Space Telescope. SNAP will be a powerful tool for a future generation
of weak lensing experiments to investigate the nature and distribution of dark
We study the accuracy with which weak lensing measurements
can be made from space, and the subsequent resolution of both
3-dimensional and projected 2-dimensional dark matter maps. As a
baseline, we use the instrumental specifications of the
Supernova/Acceleration Probe (SNAP) satellite. We compute the
sensitivity to shear as a function of depth for space-based
observations. Our predictions are based on detailed image
simulations created using `shapelets', a complete and orthogonal
parameterization of galaxy morphologies. We also estimate the
precision of the photometric redshifts which can be derived from
the SNAP filter set. The high galaxy number density afforded from
a wide survey in space allows projected dark matter maps with a
rms sensitivity of 3\% shear in 1 arcmin^2 cells. This will be
further improved using the proposed deep survey with SNAP, in
which 3D mass reconstructions will be possible with a 1sigma
sensitivity of approximately 10^(13)M_sun at z=0.25.
Space-based surveys will thus capture non-Gaussian features
arising from gravitational instability and map out the mass in the
universe with unprecedented resolution.
Weak gravitational lensing provides a unique method to directly map
the dark matter in the universe and measure cosmological
parameters. The current weak lensing surveys are limited by the
atmospheric seeing from the ground and by the small field of view of
existing space telescopes. These limitations can be circumvented using
wide field observations from space, such as those afforded by the
future SNAP mission. We study how SNAP can be used to measure the weak
lensing power spectrum and to set constraints on cosmological
parameters. This is done by computing the lensing sensitivity using
detailed image simulations and instrumental specifications studied in
earlier papers in this series. We show that the SNAP weak lensing
survey will be able to measure the matter density parameters
Omega_m and the dark energy equation of state w with high
precision. The constraints on these two parameters are comparable and
complementary to that associated with supernovae measurements.