1. R. Pain9/18/2008 LSST-SNAP complementarity Reynald Pain IN2P3/LPNHE Paris, France Page 1

2. R. Pain9/18/2008 True: 1.Target Dark Energy (and Dark Matter) as primary science 2.Use wide field imager as (main) instrument 3.Hope to start operating in ~2015 4.Are competing for (some of) the same money But … LSST vs SNAP (and vice-versa) Page 2

3. R. Pain9/18/2008 LSST & SNAP apparatus Primary mirror : ~2m Field-of-view : ~ 1 deg 2 6 filters in the visible : 320 nm -> 1100 nm 3 filters in NIR (->1700 nm) low-z spectrograph Primary mirror : 8.4 m Field-of-view : ~ 10 deg 2 6 filters in the visible : 320 nm -> 1100 nm Page 3

4. R. Pain9/18/2008 LSST & SNAP surveys SNAP Survey Area(sq.deg) Depth(AB mag) n gal (arcmin -2 ) N gal Deep/SNe 15 30.3 250 10 7 Wide 4000 27.8 100 10 8.5 Panoramic 7000-10000 26.7 40-50 10 9 LSST Survey Page 4

5. R. Pain9/18/20085 SNAP & LSST strategies for Supernovae SNAP: Area : 2x7.5 sq. deg. Cadence : 4 days Imaging and spectroscopy Total nb of SN : ~ 2000 Need for “nearby” SN (ground) Light curve modeling requires lots of SN LSST: full sky, twice a week => 250000 SN/yr ! well measured subsample at z<1 Some DE models require SN at z>1 Dust modeling requires IR meas.

6. R. Pain9/18/20086 SNAP & LSST strategies for Weak Lensing 9-band photometry (incl NIR) helps for phot-z LSST: 200 exposures per sky patch will yield negligible PSF induced shear systematics SNAP: increase the number of resolved galaxies (spatial resolution) and PSF stability Cosmic shear signal Stars SNAP and LSST will have very different systematic uncertainties

7. R. Pain9/18/2008 Rely on the same techniques (SN, WL, BAO,..) to constraint DE but use a very different instrumental approach DE is a difficult measurement. Improving on current (+ near future) constraints will be extremely difficult and will in fine come to how well one does on controlling the systematic uncertainties LSST and SNAP are complementarity in particular when dealing with systemactic uncertainties Combined, they will yield improved constraints on Dark Energy LSST and SNAP Page 7

8. R. Pain9/18/2008Page 8

9. R. Pain9/18/20089 Cosmological parameters (1st year) 68.3, 95.5 and 99.7% CL Green SNLS, Blue SDSS/BAO 2005  M = 0.271 +/- 0.021 (stat) +/- 0.007 (syst) w = -1.023 +/- 0.090 (stat) +/- 0.054 (syst)