may stars be the actors and dark energy direct shoot a movie in the sky Chihway Chang Oct.8 ‘2008

1. may stars be the actors and dark energy direct shoot a movie in the sky Chihway Chang Oct.8 ‘2008

2. outline • Why LSST ? • Science goal and science driven design • The project system • Telescope • Camera • Data management • Focal plane problem & weak lensing • Conclusion

3. The reason • What is missing in the astronomy society? • Traditional operation of telescopes • Public data available for all science use • “It will not be possible to answer the great questions in astronomy and cosmology without a technological breakthrough. we need something that goes wider, deeper, and faster than any instrument we have today.” --Anthony Tyson (UCD) • Large Synoptic Survey Telescope — let’s shoot a movie in the sky

4. Cast • ~10 billion galaxies +10 billion stars with redshift • ~1 million gravitational lenses • ~10,000 asteroids • ~1 million supernovae • Gamma ray bursts • New phenomena  Large and complete 3D sky map

5. The science goal • Probing dark energy & dark matter • Weak lensing on galaxies (WL) • Baryon acoustic oscillation (BAO) • Type Ia Supernovae • Taking an inventory of the solar system • Near-Earth objects (NEO) survey • Exploring the transient optical sky • Active galactic nuclei (AGN) • Mapping the Milky Way • Galaxy formation and evolution

6. Science-driven instrumentation • Single visit depth : NEO, variable objects • Total visit depth: extragalatic / galatic • PSF, image quality: WL • Single visit exposure time: moving objects, atmosphere, readout noise • Filter components: photometric z

7. Crew • Telescope • Telescope optical and mechanical design, calibration, building and site • Camera • Electronics, filter, shutter, cryostat, controller, guider, detectors, simulation and calibration • Data management • Image processing pipeline, data storing and public access

8. Telescope basics • 9.6 degree2 field of view (Keck ~ 0.2) • Etendue = collecting area * sky coverage ~ 320 m2 degree2 (Keck ~ 4) • Three mirror Paul-Baker: • M1 8.4 m primary • M2 3.4 m convex secondary • M3 5.0 m tertiary (monolithic design) • L1 L2 L3 (refractive corrector)

10. University of Arizona's Steward Observatory Mirror Lab

12. Too much data! • (4 byte per pixel) * (32 billion pixels per exposure) * (continuous 15 or 1 sec exposures) ~ 1.6 GB/sec • One pass ~ 20,000 square degrees ~ three nights of observation ~ 150 TB • Overtime ~ 31,000 square degrees ~ 5 years of observation ~ 30 PB (whole sky ~ 41,253 degree2 )

13. No big deal…

14. Challenge • Technology: high data rate, real-time analysis, later data exploration • Computational cost: PB disk storage system  $1 million in five years, this price should drop to well below $100,000 • National Virtual Observatory

15. A man-size camera • 1.6 * 1.6 * 3 m3, 2800 kg • (64 cm)2 flat focal plane with 3.2G pixels • Focal plane operate at -100 degree C • Six 75cm filters UVBRIY

16. Filters • 5 band from SDSS ugriz + y • Photometric redshift: linear regression fitting of spectral energy distribution (SED) templates • Y band: designed to probe high z objects

17. Photometric redshift By Anthony Tyson

18. Cryostat and contamination test

20. Focal plane

21. Focal plane flatness and weak lensing

22. Dark energy and dark matter • The visible mass and known matter cannot explain the why the Universe behaves • How to “see” DM: • rotational speeds of galaxies • orbital velocities of galaxies in clusters • gravitational lensing • How to “see” DE: • baryon acoustic oscillation • SN

23. Weak lensing basics • Gravity bends light • Map of dark matter • Method: • Use stars to construct PSF map • Deconvolve galaxy with this PSF map • Measure residual ellipticity to infer shear • Lensing signals are typically WEAK • Accurate “shape” measurement is crucial • The misalignment of the optics can easily distort image shape and mimic shear • LSST may have more difficulties because the focal plane is enormous

26. 10 um defocus

27. The simulator • John Peterson @ Purdue • Include science: • Kolmogorov density screen generator multi-layer frozen screen atmosphere • ray-tracing refraction and reflection of mirrors and lensing • Zernike distortions on mirror surfaces • 6 degree of freedom motions for the optical elements refraction • photo-electron conversion and diffusion in silicon • charge saturation and blooming

29. Basic checks • Optics • Background • PSF changes

30. Build in • Potato chip shapes • Characterize and analyze PSF

31. Where is this going? • Removing instrument signature from weak lensing data • Understand the limit of weak lensing using LSST • Set specs on CCD manufacture

32. Conclusion • LSST is based on the concept of “fast, wide, deep” as opposed to traditional astrophysics projects. • The instrumentation of LSST require high technology and complete understanding of the physics involved. • Good instrumentation makes doing science easier. • The data of LSST will be available on line to anyone who is interested in it. • 2014 – Let the movie begin…

34. Reference • http://discovermagazine.com/2008/may/13-movie-camera-to-the-stars • http://www.lsst.org/lsst_home.shtml (LSST official website) • LSST: FROM SCIENCE DRIVERS TO REFERENCE DESIGN AND ANTICIPATED DATA PRODUCTS (LSST overview paper)

35. THANKS