# Presentation: 085527

## Weak Lensing from Space with SNAP

**Alexandre Refregier (IoA)**
**Richard Ellis (Caltech)**
**David Bacon (IoA)**
**Richard Massey (IoA)**
**Gary Bernstein (Michigan)**
**Tim McKay (Michigan)**
**Bhuvnesh Jain (U. Penn)**
**for the SNAP Lensing Working Group**
**Cambridge Workshop - July 2001**

## SNAP: SuperNova Acceleration Probe

- SNAP:
-  ~2 m telescope in space
-  1 sq. degree field of view
-  0.35-1.7m imaging and (low-res) spectroscopy
-  0.1” PSF (FWHM)
-  dedicated survey mode
-  Wide field imaging from space

- Institutions: LBNL (P.I.), U. Berkeley,
- CNRS/IN2P3/CEA/CNES, U. Paris VI & VII,
- U. Michigan, U. Maryland, Caltech, U. Chicago,
- STScI, U. Stockholm, ESO, Instituto Superior Tecnico

## Mission Overview

**Simple Observatory consists of :**
**1) 3 mirror telescope w/ separable kinematic mount**
**2) Baffled Sun Shade w/ body mounted solar  panel and instrument radiator on opposing side**
**3) Instrument Suite**
**4) Spacecraft bus supporting telemetry (multiple antennae), propulsion, instrument electronics, etc**
**Almost no moving parts (ex. filter wheels), rigid simple structure.  **

## Orbit

- High Earth Orbit (38 Earth radii):
-  Minimal thermal Changes
-  Excellent telemetry (all
-    the data is sent down to 3
-    ground stations)
-  reduced and controlled
-      systematics

## Camera

-  132 large format CCDs and 25 HgCdTe devices
-  ~0.1’’ pixels
-  8 visible and 3 IR filters
-  About 1 billion pixels
-  Field of view; 1 sq. deg.

**GigaCAM**

## SNAP Surveys

**SNAP Surveys**

- Hubble Deep Field

- Weak Lensing Survey

- Supernova Survey

**Surveys**:
-  Supernova Survey:
-  20 sq. deg.
-  2.5 years
-  R<30.4 (11 bands)
-  Weak Lensing Survey
-  300 sq. deg.
-  0.5-1 year
-  R<28.8 (11 bands)

- Large number of exposures
-   (1 frame every ~4 days)

## Mission Status

-  Currently in the Study Phase of the project (funding from DoE and NSF)
-  Feasibility was demonstrated (reviewed by Goddard Integrated Mission Design Center, NASA)
-  Reviewed by a number of Agency committees (DoE, NSF, NASA) and by Peer Committees (ex. NRC committee on the Physics of the Universe)
-  Expect to submit the proposal within a year or two
-  Goal: fly by 2008 (about 4 years from approval to launch)
-  Mission duration: 3 years, but expected to continue for several further years if funded
-  Public archival data

## Advantage of Space for Weak Lensing

-  larger surface density of resolved galaxies
-  very reduced impact of the PSF smearing
-  more shape information

##   Strengths of SNAP for Weak Lensing

- Wide field in space - large survey area with exquisite 	                               image quality
- Depth of survey -  reduced shot noise and mapping  	resolution
- Many photometric bands - evolution of structure as function
- 	of  redshift
- Small PSF, Thermal stability, stringent optical requirements, multiple exposures - greatly reduced systematics

## Mapping the Dark Matter

- LCDM
- 0.5x0.5 deg
- Jain et al. 1998

## Lensing Power Spectrum

- CDM

- CDM (linear)

- OCDM

**SNAP WF survey [300 deg****2**** ; 100 g arcmin****-2****; HST image quality]**

## New cosmological constraints

- Variance:

- Skewness:

***Data will break current degeneracies (e.g. ************M****** and ************8 ******;****** ************M****** and w )***

- Cf. Bernardeau et al. 1997

## Power Spectrum with Dark Energy

- Use the non-linear power spectrum for quintessence models of  Ma, Caldwell, Bode & Wang (1999)
-  The Dark Energy equation of state (w=p/****) can be measured from the lensing power spectrum
-  But, there is some degeneracy between w, M and 8

## Complementarity of Weak Lensing and Supernovae

**Weak Lensing + CMB**

- Weak Lensing breaks degeneracies in ***w-Omega ***plane. Does ***w ***vary***?***

## Systematics: Ground vs Space

- Systematics

- Noise

- Noise and Systematics
- are greatly reduced in
- space

## Conclusions

-  SNAP will open the window of wide field imaging from space
-  Ideal instrument for weak lensing, which complements Sne
-   (Dark Energy+Dark Matter)
-  Systematics are likely to be much reduced
-  SNAP will yield a map of the dark matter,  and a precise
-   measurement of the evolution of structures
-  Complementary to wide-field ground based survey