Prospects for the Dark Energy Survey

1. Prospects for the Dark Energy Survey Including an Overview of the Dark Energy Camera’s Central Nervous System Kyler Kuehn Center for Cosmology and AstroParticle Physics, The Ohio State University CCAPP Symposium Columbus, OH 14 October, 2009

2. Life, the Universe, and Everything • Dark energy can be described in terms of an equation of state: w(z) = p/; we parameterize w(z) as follows: w(z) =w0+wa(1–a), where a=(1+z)-1

3. Dark Energy Survey Science Goals: constraints on w0 and wa w(z) =w0+wa(1–a) • DES will measure the expansion history of the Universe through the dependence on redshift of the luminosity distance, angular diameter distance, and volume element and the growth rate of structure. • Three observing techniques will measure the (3-D) spatial distribution of 300M galaxies in four bands to ~24th magnitude. The fourth, a search for SNe Ia, will yield independent constraints on Dark Energy, along with an independent measure of systematic errors.

4. Additional DES Science Beyond Supernovae, Galaxy Cluster/BAO studies, Large Scale Structure, and Weak Lensing, DES will contribute to progress in (among other topics)… • Photometric redshift estimation methods • N-body LSS Simulations • Strong Lensing • Non-Type Ia SNe • Other transients (e.g. GRBs), through detection and follow-up, as well as pre-discovery images; transient host properties; multi-wavelength and multi-messenger campaigns • Galaxy Properties and Evolution: QSOs, luminosity functions, stellar populations, DM Halo correlations, interacting galaxies • Milky Way/Local Group “Archaeology”: Galactic (sub-)structure, stellar metallicities (e.g. 47 Tuc), variable stars, proper motions

5. Focal Plane and Survey Characteristics Focal plane with 62 2k x 4k Image CCDs: ~520 Mpixels  ~1GB images (+ header) 8 2k x 2k Focus/ Alignment CCDs 4 2k x 2k Guide CCDs • DES incorporates two multiband surveys: • Main Survey: “Tiled” pointings of 3 deg2 each, covering an area of 5000 deg2 twice per year in each of four filters • - SNe Ia Survey: 9-15 deg2 within Main Survey field • - Filters: g, r, i, z, Y, from DES augmented with J, H & K from VISTA Survey • Surveys will take place during 2011-2016 (525 nights). Additional nights allow significant opportunities for Community Use of DECam.

6. DES Instrument: DECam Mechanical Interface of DECam to the Blanco CCD Readout Filters Shutter Hexapod Optical Lenses

7. Dark Energy Camera CCDs • LBNL CCDs: • 31.5 mm x 63 mm • 250 μm thick, fully depleted • 2 Readouts per chip • 2k x 4k pixels @ 15 μm (0.28”)/pix • Extremely red sensitive: QE > 50% at 1000 nm Fabrication and testing at Fermilab have yielded nearly a full focal plane of science-grade devices

8. Science Data Flow SISPI Overview Officially title: “Survey Image System-Process Integration” (SISPI) Software Infrastructure also known as “Mountaintop Software” or the “DECam Central Nervous System” Testing non-DES + simulated images, along with related telemetry data. Data Transport System

9. Infrastructure/Applications Schematic

10. Feedback to Observer • Real Time Display • Full (compressed) focal plane image of every exposure • Instrument Heath • SISPI process that accumulates information from ICS,FCS, TCS and prepares time-history plots, alarms… • Image Health • Within Image Builder; Very fast “SExtractor-Lite” check of CCDs: Sky BG (“Is this thing on?”), Bright Star PSF & Shape Properties • Quick Look • Interactive observer workstation • Display a copy (using DS9 or similar package) of every image • Quick Reduce • More sophisticated image processing on complete images • Sampling datastream every N (~5) images

11. Real-Time Image Display Original Image Compressed Image 1GB  4MB (~1/256 compression) in < 1 sec.

12. Instrument Health Instrument Health displays current parameter value and time history plot.Any parameters generated by site, telescope, or camera telemetry can be displayed.

13. Image Health • imagehealth.c (incorporating cfitsio library): • Sets chip stepsize, defines object by threshold above image mean and number of pixels to search around bright pixel • Opens image (currently from disk), checks image header for keyword values (e.g. saturation, axis size), defines number of chips in MEF file • Reads pixel values to data structure • Finds mean of (non-saturated) pixel values • Gets bright pixels (pixel value ≈ saturation/2)  defined as object • Finds all pixels in object—if saturated, pick new object • Calculates image/object statistics: Flux, FWHM, Object BG, Sky BG, Major [Minor] Axis, Ellipticity, Orientation Angle • Iterate over all chips • Output provided for Image-by-Image and Time History Displays

14. IH Execution with MEF FITS Images Sample Pixel Positions of IH Objects • User-defined parameters include: • “Full Counting” or “Pixel Skipping” mode (latter mode is faster, with little loss of accuracy) • Object Searchbin Size • Object Intensity Threshold • Pixel Saturation Value (option to read value from FITS Header) • Object Size Requirements (for cosmic ray rejection) • Limit to Number of Potential Objects • With DES images consisting of 124 amplifiers (2 per chip), ~100 objects found by IH, with some filter/threshold dependency • Object search starts at position 0,0, but no start bias evident in output object positions.

15. ImageHealth Output Testing • Compare ImageHealth to SExtractor ( = “truth”) Sample results for Mean(IH–SE), full counting (pixel skipping = 8): • ΔPosition: 1.81 (1.72) pix • ΔBG: 0.35 (0.24)% • ΔFlux: 0.53 (0.68)% • ΔFWHM: 0.22 (0.24) pix • ΔEllipticity: 0.03 (0.04) • ΔAngle: 8.6° (7.4°), or 5.0° (3.7°) excluding 5 largest outliers • Low Quality Images (large FWHM) in Blanco data identified routinely • ImageHealth is not instrument-specific! • DES grizy images: initial tests complete, more detailed tests underway • Y4KCam science, engineering images (courtesy of R. Pogge) • Blanco (Coma Cluster) images • “SExtractor-Lite”: streamlined processing with more focused output • ~600 lines of code (cf. 1700 for SExtractor) • Distinct file I/O and object analysis (not the case for SExtractor) • Executes in 30 seconds in full counting mode or as little as 6 seconds in pixel skipping mode (cf. 70 seconds for SExtractor)

16. DECam Infrastructure: Under Construction • DES expects first light in 2011/2012. Its five year mission: to explore 5000 deg2 of the Southern Sky, to seek out faint galaxies and new supernovae, to provide constraints on the Dark Energy Equation of State that no one has provided before. • SISPI (the “Central Nervous System” of the Dark Energy Camera), is in the “prototype” stage, with working components being tested at Fermilab and on the sky at CTIO. • ImageHealth toolkit will be extremely useful for DES collaboration, as well as any other astronomers needing real-time analysis of large (GB) images.

17. Committee on the Internationl Freedom of Scientistshttp://www.aps.org/about/governance/committees/cifs/index.cfm • “To achieve its full potential and to benefit all mankind, science requires that governments respect basic human rights, allow open communication, and avoid interference with the rights of scientists as they carry out their professional work.” -- from the APS Statements on Human Rights • “This Committee shall be responsible for monitoring concerns regarding human rights for scientists throughout the world. It shall apprise the [Society] of problems encountered by scientists in the pursuit of their scientific interests or in effecting satisfactory communication with other scientists and may recommend appropriate courses of action designed to alleviate such problems.” -- from the APS CIFS Statement of Purpose • Cases currently being reviewed from China, Cuba, Gaza Strip/Israel, Iran, Iraq, Mexico, Saudi Arabia, Turkey, Russia, and the United States, involving allegations of everything from scientists being unfairly tried and incarcerated to students prevented from traveling internationally to participate in educational opportunities. • CIFS also participates in the awarding of the APS Andrei Sakharov Prize, “to recognize outstanding leadership and/or achievements of scientists in upholding human rights.”