1. The Dark Energy Survey The Big Questions The Discovery of Dark Energy
The telescope
The camera
The science
Expected Results

2. The Big Questions What is the universe made of?
Where in the universe are we?
When in the universe are we?
How does Fermilab help with these questions?

3. What is the Universe Made Of?

4. Where are we in the Universe?
Our galaxy, the Milky Way, is a spiral galaxy similar to this one (called M81). M81 is 12 Million light years away. Arrow shows where our sun would be if this were the Milky Way

5. How Far We’ve Come Since 1920’s
Hubble Space Telescope
Hubble Middle School
In 1920, state of knowledge: our galaxy = the universe, but contained many “nebulae” (fuzzy, unresolved clouds)
By 1929, Edwin Hubble had established that nebulae were galaxies like ours, very far away AND that they were almost all receding, at faster speeds if they were farther away
Edwin P. Hubble ( )
(Grew up in Wheaton, IL
U of C graduate, also played basketball)

6. Where are we in the Universe?
160 billion
over entire sky
10,000
here

7. When are we in the Universe?

8. How Fermilab is helping answer these questions
Matter at the level of quarks and leptons
CDF and DØ, ATLAS and CMS
Neutrino experiments (MINOS, MiniBooNe, Noνa)
Dark Matter searches
CDMS, COUPP, DAMIC
CDF/DØ, ATLAS/CMS
Dark Energy measurements
Sloan Digital Sky Survey (completed)
Dark Energy Survey (being constructed now)

9. How Dark Energy Was Discovered
Image courtesy of David A Hardy
Supernovae: “Standard Candles”
Allow us to measure the expansion of the Universe as we look back in time

10. The Dark Energy Survey

11. What is the Dark Energy Survey?
Will survey 5000 square degrees of the Southern Hemisphere sky, repeatedly using different filters to capture different wavelengths of light
Will take images of more than 300,000,000 galaxies, reaching back to a redshift of 1.3 (~7.7 billion years for the light to reach us from the farthest galaxies we will see)

12. Cerro Tololo Inter-American Observatory
Altitude 2215 m
Climate dry and mild – among the best sites for astronomical observation

13. The Blanco Telescope

14. The Blanco Telescope
The mirror is 4 m in diameter, made of a single piece of Cervit glass
Here the mirror is being removed for re-aluminization

15. Popular Science, September 1969

16. The Dark Energy Camera
Imager

17. DECam Imager A 520M pixel digital camera
DECam Focal Plane
A 520M pixel digital camera
Has a 3-square-degree field of view
Contains 74 CCDs which need to be operated in a vacuum and at a temperature of -100 degrees C
Uses custom built very-low-noise readout electronics
Each image taken by the camera is 1 GB in size
Prototype Imager

18. DECam CCDs Each CCD: 4K x 2K pixels Converts light to charge
Charge from each pixel is moved along the chip and read out sequentially
Very efficient for red/ infrared light (design by LBNL)

19. The Dark Energy Camera
Optical Corrector

20. DECam Optical Corrector
C2 & C3 C4 C5
Filter-changer and shutter chamber (two filters shown)
C1 cover
Internal stray light baffle
Electrical
isolator

21. DECam Optical Corrector
Contains 5 fused silica lenses – largest is about 1 m in diameter
The lenses are carefully designed to produce the best focused image at the location of the plane of CCDs
They have taken about two years to manufacture

22. Focusing the Camera Hexapod positions camera to 1 micron
Camera weighs ~8000 lbs

23. Testing DECam
We will place the camera in a specially built stand to tilt and rotate it
Allows us to verify operation in all orientations before shipping it to Chile

24. The Testing Stand for DECam

25. Fixtures for Mounting Imager on the Telescope

26. How does the survey work?
Take data for about 100 nights each year for 5 years (the survey area is visible from Oct-Feb)
Obtain about 300 images per night
Send data to NCSA at Univ of Illinois for processing
Raw dataset: ~150,000 images
Processed dataset: > 1 petabyte of data

27. Science with DECam
We expect to identify 300,000,000 galaxies, galaxy clusters and 2000 new supernovae
Identify distance for each galaxy and supernova by comparing its light intensity in the 5 different DECam filters (For some fraction of objects, get more precise distance measurement using other telescopes)

28. Science with DECam
The supernovae will give us an independent measure of expansion with a new dataset, similar to what other surveys have done but out to a larger distance
How the density of galaxies varies with distance will also tell us how the metric of the universe has changed over time, and thus whether the expansion we see has been constant over that time

29. Science with DECam cont’d
Look for ‘bending’ of light from distant sources around massive galaxy clusters which are closer to us

30. Systematic Errors
Worry about effects of dust causing supernova to be less standard
Worry about correctly identifying and measuring the distance for very faint galaxies
Worry about correcting for the effects of changes in the instrument over time
Worry about effects from the atmosphere

31. Results: A measurement of Dark Energy which is ~ 5 times better than current measurements

32. Further results
A very capable instrument on a fine telescope at an excellent site
A library of 300,000,000 astronomical objects available for other scientific studies
Can be correlated with results from other instruments