Dark Energy and the LSST

1. Dark Energy and the LSST Christopher Stubbs John Oliver Peter Doherty Nathan Felt Meghna Kundoor Gautham Narayan Amali Vaz Harvard University Laboratory for Particle Physics and Cosmology DOE Site Visit Sept 20, 2010

2. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

3. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

4. preposterous Emergence of a Standard Cosmology Our geometrically flat Universe started in a hot big bang 13.7 billion yrs ago. It has been expanding ever since. The evolution of the Universe is increasingly dominated by the phenomenology of the vacuum, the “Dark Energy”. “Dark matter”: what is it? Ordinary matter is a minor component. Luminous matter comprises a very small fraction of the mass of the Universe.

5. Large Synoptic Survey Telescope Top ranked ground-based project in 2010 Decadal Survey Optimized for time domain scan mode deep mode 10 square degree field 6.5m effective aperture 24th mag in 20 sec >20 Tbyte/night Real-time analysis Engineered to minimize systematics for Dark Energy

6. Our efforts on LSST… • Stubbs has long-standing engagement and leadership role in LSST: • Past member of LSST Board of Directors • Original LSST Project Scientist • Current member of LSST Science Council • Coordinator for DOE efforts on SN cosmology • Likely head of system commissioning team • Co-author on LSST Science Book • Laid intellectual foundation for calibration scheme • Adopted by LSST, by Dark Energy Survey… and others And the 12 ft diameter LSST secondary mirror is sitting in our lab…

7. LSST Camera system: • electronics development, • back end modules LSST Detector Test and Characterization: • Detector test system is here • Responsibility for device testing and optimization LSST Calibration system: • Conceptual development and refinement • Laboratory development of projector system • Same philosophy being adopted for DES. Preparing for LSST Data Analysis: • Optimal data reduction techniques and analysis • Supernova observations as a probe of dark energy • Minimizing system uncertainty budget for supernova cosmo.

8. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

9. LSST Focal Plane Overview Cryostat Assembly 21 “Science Rafts” 4 special purpose “Corner Rafts” for guiding and wavefront sensing 16 Mpixel CCD image sensors ~3.2 Gpixels total

10. Requirements • Large focal plane ~ 3.2 GPixels • Rapid exposures  back to back 15 second (cosmic ray rejection) • Low dead time  2 second readout • Low read noise  6 e rms (limited by sky shot noise) • Read time and noise specs can only be met by highly segmented sensors and highly parallel readout. •  1 readout channel per megapixel •  3,200 readout channels • High density ASIC based readout system “a la hep”.

11. LSST Raft Tower Electronics Electronics must live in “shadow” of raft 9 Sensor Raft – 144 Readout channels Raft Tower Assembly Raft • 6 Back End Boards • 24x 18 bit video ADCs/Board • “Slo-controls”, thermal control, etc • 1 “Raft Control Module” • Readout state machine (sequencer) • Data collection + fiber optic to DAQ • Slow control processing FEE BEE Harvard Deliverable

12. LSST Electronics Status • Back End Electronics – Harvard deliverable Status • All boards in 2nd or greater version • Current version supports 144 readout channels, fiber optics, etc. • Under test – ADC performance measured • Integration with FEE and DAQ  Ongoing • Raft Control Crate fully designed. Multiple copies will be made available for testing in collaboration. • Firmware development continuing for BEB & RCM • Full system status • 2nd generation ASICs tested • 3rd and final generations in design • 2nd generation FEB completed. Under test. U. Penn • 2nd generation BEB under test in Raft Control Crate – Harvard • Vertical Slice testing – In progress, will continue through CD1 and beyond • Additional Raft Control Crates under construction for collaboration use

13. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

14. LSST Detector Test Overview • Multiple Test Facilities (BNL, LPPC, etc.) • Multiple Detector Vendors (E2V, ITL, others?) • Stringent Requirements (flatness, PSF, QE) • Comprehensive Testing and Characterization • Repeatability, Reproducibility, Consistency • 189 Sensors in LSST Focal Plane! • Led By Paul O’Connor (BNL)

15. LSST Detector Testing at LPPC Current LPPC Efforts : • Detector Test Stand Hardware Management • Preparation and Validation of Test Hardware • Electro-Optical Testing of Candidate Detectors • Development of Test Software • Establishing Detector Test Standards LPPC Strengths: Decades of Experience in CCD Image Sensor Test A Rapidly Growing Role for LPPC in LSST Detector Test

16. Detector Test Stand Hardware Management Managing the acquisition and distribution of detector test electronics to all test sites: Brookhaven National Laboratory Harvard LPPC L'Institut National de Physique Nucléaire et de Physique des Particules (IN2P3) SLAC/UC Davis Purdue University Managing the Standardization of Test Facilities

17. Validation of Test Hardware Currently finishing assembly and validation of BNL cryostat for testing E2V candidate sensors in Oct/Nov 2010 timeframe Preparing for integration and test of ITL candidate sensors at LPPC in Nov/Dec 2010 timeframe Working with IN2P3 to finalize detector test facility in Paris Coordinating development of a new test facility at Institute of Physics, Academy of Sciences, Prague

18. Electro-Optical Testing of Candidate Detectors LPPC has a long-established detector test facility that has been used on multiple projects: PISCO, Pan-STARRS, LSST, etc. LPPC is constructing a new detector test facility specifically for LSST image sensors (lab space courtesy of Dr. Franklin) LPPC has more experience in the testing of CCD image sensors than any other institution in the LSST collaboration Working in close collaboration with LSST partner institutions to support device testing at multiple locations STA/ITL Prototype Imager E2V Prototype Imager

19. Development of Detector Test Software Multiple test facilities require the ability to reduce image data with consistent results Currently multiple sites use diverse software toolsets • Good for development phase (diverse ideas, techniques, etc) • Bad for the long term (consistency, coherence, etc) LPPC will assist existing developers to standardize on a set of software tools for use across the collaboration LPPC will draw on tools in use both at LSST partner sites, industry standard tools, and its own extensive library of CCD test data reduction code

20. Establishing Detector Test Standards LPPC is • Leading the effort to standardize the image data set required for device characterization • Working to formalize image header keywords for consistency across facilities • Coordinating the effort to standardize the software tools used to reduce detector test data • Helping create a standard detector test report for use at all facilities engaged in LSST image sensor testing

21. Near-Term LPPC Detector Test Goals • Delivery of detector test cryostat to BNL for E2V detector test (10/2010) • Characterization and optimization of ITL detector prior to NSF PDR and DOE CD-1 (11-12/2010) • Completion of new test facility (12/2010) • Definition of standardized image file header keywords (12/2010) • Preparing to integrate detector test and Raft Tower Electronics for ‘Vertical Slice Test’

22. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

23. Passbands and System Sensitivity

24. Pushing to Better Precision • LSST promises considerable advances over current capabilities • The requisite flux precision for pushing to the next level of characterization of the Dark Energy is < 1% • Supernova distance measurements • Photometric redshifts for weak lensing measurements, and BAO analysis. • Inadequate corrections for variable atmospheric transmission will be a leading source of systematic error. • SDSS achieved few-percent precision all-sky, while differential measurements in single frames reach part per thousand levels • We are nowhere close to the Poisson limits for objects with SNR > 100. Why?

25. Galactic scattering Broadband photometry Source Atmosphere Instrumental transmission Four aspects to the photometry calibration challenge: Relative instrumental throughput calibration (i.e. get the flux ratios right) Absolute instrumental calibration (This is far less important) Determination of atmospheric transmission Determination of Galactic extinction (most stars lie behind the extinction layers). Historical approach has been to use spectrophotometric sources (known S()) to deduce the instrumental and atmospheric transmission, but this (on its own) is problematic: integral constraints are inadequate, plus we don’t know the sources well enough.

26. Our Basic Philosophy for LSST Calibration • Use precisely calibrated NIST photodiodes as the fundamental metrology basis for flux measurements. • Measure instrumental throughput relative to known photodiode. • Measure atmospheric transmission function directly. • Deliver, for each photometric measurement, the effective passband through which it was obtained. Stubbs & Tonry, ApJ 646, 1436 (2006)

28. Stubbs et al., ApJ in press

29. LSST Calibration Screen Optics - Ms. Amali Vaz

30. Accelerometers on LSST calibration telescope

31. Atmospheric Transmission Stubbs et al., PASP 119, 1163, 2007.

32. So we need to measure (or determine) • Extinction due to clouds, and transparency variations: This can be bootstrapped if a given field is observed many times, some in cloud-free conditions. Tougher if only a few visits per band. • Aerosols: time variable and tough to measure well. • Water vapor: differential photometry or spectroscopy, or precise dual-band GPS? • Barometric pressure, for MODTRAN input. Similar challenges for cosmic ray experiments: Auger, Veritas, et

34. Differential Narrowband Water Monitor • Simultaneous measurements on-band (940 nm) and off-band (880 nm) using stars to back-light atmosphere. • Proof-of-principle data shows promising results 300 mm f/2.8 1K x 1K deep depletion CCD 940 nm 880 nm

35. Dual-band Geodetic-Quality GPS Water vapor in atmosphere produces difference in arrival times for GPS signals at two different wavelengths (1.575 and 1.228 GHz). http://www.gpsworld.com/files/gpsworld/nodes/2002/721/chart3.jpg

36. A universal observed stellar locus • Disk M dwarfs with metallicity [Fe/H] > 0.7 all from closer than ~1 kpc so minimal sensitivity to metallicity gradients • Main sequence disk stars and evolved halo stars High et al., AJ 138, 110, 2009

37. Introduction to the Dark Energy Crisis, and LSST LSST Camera electronics development LSST Detector testing and optimization Improved Precision for Dark Energy Characterization Addressing the Challenges of LSST Exploitation

38. Refining supernova light curve analysis:LSST won’t have supernova spectroscopyHost extinctionredshift extractionIb, Ic contamination…

39. Is the accelerating expansion the same in different directions? A. Diercks’ PhD thesis, UCSB, 1999 Cook & Lynden-Bell, MNRAS 401, 1409 (2009), and references therein

40. LSST: Plans for FY2011 • Camera electronics engineering • Detector device testing and characterization • Continue to refine and test innovative calibration methods • Establish SN dark energy working group, with LBL and Fermilab, refine light curve fitting • Develop instrument calibration and atmospheric monitoring apparatus.