1 The Dark Energy Survey (DES) Douglas L. Tucker (Fermilab) DES Calibrations Scientist Southern Connecticut State University, 12 March 2010

2 Part 0: Some Background The Universe is Expanding The distance between galaxies increases with time The wavelength of light grows with time at the same rate (In this 2D representation, imagine yourself at the North Pole of this expanding globe…)

3 Part 0: Some Background Cosmological Redshift (z) … is the redshift caused by the expansion of the Universe: R 0 / R = (1+z) where R 0 is the “size” of the Universe now, and R is the “size” of the Universe at redshift z. It can be measured by the shift in wavelength of lines in the spectra of distant galaxies: λ / λ 0 = (1+z) where λ 0 is the rest-frame wavelength and λ is the observed wavelength for redshift z. Z=0.004 Z=0.05 Z=0.07 Z=0.13 Z=0.20

4 Part I: What is Dark Energy? To begin to answer this question, we must first consider what makes up the total mass-energy density of the Universe...

5 What is the Universe Composed of? “Normal Matter” (protons, neutrons, electrons, etc...) Luminous NGC 2403 ~20 kpc SDSS (Optical) ~250 kpc Fornax Cluster Chandra (X-ray) [ 1 parsec = 3.26 light-year, and 1000 parsecs = 1 kiloparsec (1 kpc) ]

6 Horsehead Nebula Credit: NOAO/AURA/NSF What is the Universe Composed of? “Normal Matter” (protons, neutrons, electrons, etc...) Non-luminous (Baryonic Dark Matter)

7 Non-Baryonic Dark Matter Cold Dark Matter (non-relativistic velocities) (“WIMPs” = Weakly Interacting Massive Particles) What is the Universe Composed of?

8 Incidentals Neutrinos with non-zero restmass Neutrino Oscillation measurements: m e > 0.1 eV Hot Dark Matter (relativistic velocities) Cosmic Microwave Background photons T=2.73K E=mc 2 All-sky map of CMB photons from ~380,000 years after the Big Bang WMAP-5 What is the Universe Composed of? Credit: WMAP Science Team

9 Until 1998, these seemed to be all there was... In that year, two independent groups discovered evidence for another, major component of the mass-energy density of the Universe. -- Supernova Cosmology Project -- Perlmutter et al. -- High-Z Supernova Project -- Riess et al. What is the Universe Composed of? 1998 and 2003 Science breakthroughs of the year

10 What is the Universe Composed of? These two teams were using supernovae in other galaxies as “Standard Candles” to measure the deceleration of the expansion of the Universe due to the mutual gravitational attraction of the mass within the Universe. Average Distance Between Galaxies Time since Big Bang Standard Candles Astronomical objects which, as a class, have very uniform intrinsic luminosities (intrinsic brightnesses) Can use inverse square law to determine their distances

11 SN2001V (Type 1a) Credit: Rafael Ferrando Type Ia Supernovae (SNe Ia)  Very luminous at peak luminosity, ~ 5 billion times the energy output of the Sun can be seen over cosmological distances  Very uniform after correction, the scatter in the peak luminosity for a sample of SNe Ia is only about 10-15%  Moderately numerous ~ 1 SNIa / galaxy / 100 years  The SN Ia Mechanism an accreting White Dwarf with a mass near the Chandrasekhar limit (1.4 M sun ) undergoes a massive thermonuclear explosion, completing disrupting the star light curve powered by radioactive decay of 56 Ni and 56 Co generated in the explosion into 56 Fe. Type Ia Supernovas as Standard Candles

12 Perlmutter, Physics Today, April 2003 Measurements of Dark Energy via SNe Ia Before the discovery of Dark Energy

13 Perlmutter, Physics Today, April 2003 Measurements of Dark Energy via SNe Ia After the discovery of Dark Energy

14 Perlmutter, Physics Today, April 2003 Measurements of Dark Energy via SNe Ia Acceleration --> Dark Energy is a repulsive force counteracting gravity!

15 Location of this peak is very sensitive to total mass-energy density of the Universe Further Evidence via the CMB: Baryonic Acoustic Oscillations Characteristic angular scale set by sound horizon at recombination: Standard ruler (geometric probe) Need Dark Energy to explain total mass-energy density of the Universe.

16 (0.03%) (0.47%) (4%) (25%) (0.5%) (70%) CMB Photons Ω = (0.01%) What is the Universe Composed of?

17 A Cosmological Constant?  Einstein's “Blunder” (originally added to make Universe static)  Vacuum energy  “Fine Tuning Problem”: observed value too small The decay of a new, ultralight particle? Evidence for extra dimensions? Breakdown of General Relativity? We don’t know. What is Dark Energy?

18 Consider the “size” R of the Universe at some time t compared with its “size” R 0 at the present-day... Density of matter  m =  m,0 x (R 0 /R) 3 Density of radiation  rad =  rad,0 x (R 0 /R) 4 Density of dark energy   =  ,0 x (R 0 /R) 3(1+w) –Equation of State parameter w ≡ P/  c 2 –for a cosmological constant, w = -1, or   =  ,0 –for a “Big Rip”, w < -1 –w might vary with time (w’) Recall that R 0 /R = (1+z) –E.g., at z=2, the Universe was 1/3 rd the size it is today (at z=0) How does Dark Energy Behave? Recall that z is the “Cosmological Redshift”

19 Currently, observations are consistent with Dark Energy being a cosmological constant (w=-1)    =  ,0 (density constant with time)  w ≡ P/  c 2 = -1 ⇒ P = w  c 2 ⇒ P = -  c 2 ⇒ negative pressure! Consider a piston chamber containing normal gas  expansion leads to reduction in energy density / cooling of gas  (positive) gas pressure is doing work on piston For a cosmological constant, however, the energy density remains unchanged (total energy increases)! dW=PdV How does Dark Energy Behave?

20 Probing Dark Energy: I. Geometry 1.Standard Candles Expansion rate of the Universe as a function of time Basically makes use of the inverse square law to estimate distances (time since Big Bang) 1.Standard Rulers Curved (Riemannian) vs. Flat (Euclidean) Space time Angular sizes of objects of known physical size vs. distance Average Distance Between Galaxies Time since Big Bang

21 Galaxy clustering as a function of redshift depends on the characteristics of Dark Energy (among other things) Measure mass, number, and spatial distribution of galaxies and galaxy clusters as a function of z (time) 43 Mpc (present day) see Credit: Andrey Kravtsov Probing Dark Energy: II. Growth of Structure

22 Conclusion to “Part I: What is Dark Energy?” We don’t know what Dark Energy is, other than some mysterious force that appears to counteract the effects of gravity on cosmological scales. We do have ways of measuring the effects of Dark Energy (e.g, via geometric measures and measures of the growth of structures in the Universe). We also have ways to parameterize Dark Energy (e.g., the Dark Energy equation of state parameter, w, and its derivative with respect to time w’ (or a variation of w’ called w a ).

23 Part II: What is the Dark Energy Survey (DES)?

24 The Dark Energy Survey (DES) Plan: –Perform a 5000 sq. deg. survey of the southern galactic cap in 5 optical and near-infrared filters (g, r, i, z, y) –Measure dark energy with 4 complementary techniques Cluster counts, weak lensing, baryonic acoustic oscillations, supernovae New Instrument (DECam): –Replace the prime-focus cage on the CTIO Blanco 4m telescope with a new 2.2° field-of-view, 520 Mega-pixel CCD camera + optics Survey: –525 nights during (September - February) –30% of the telescope time

25 DES Participating Institutions Fermilab University of Illinois at Urbana-Champaign University of Chicago Lawrence Berkeley National Laboratory University of Michigan NOAO/CTIO Spain-DES Collaboration: Institut d'Estudis Espacials de Catalunya (IEEC/CSIC), Institut de Fisica d'Altes Energies (IFAE), CIEMAT-Madrid United Kingdom-DES Collaboration: University College London, University of Cambridge, University of Edinburgh, University of Portsmouth, University of Sussex The University of Pennsylvania Brazil-DES Consortium: Observatorio Nacional, Centro Brasileiro de Pesquisas Fisicas, Universidade Federal do Rio de Janeiro, Universidade Federal do Rio Grande do Sul The Ohio State University Argonne National Laboratory Santa Cruz – SLAC – Stanford Consortium 13 participating institutions and >100 participants

26 Basic Survey Parameters Survey Area Overlap with South Pole Telescope Survey (4000 sq deg) Overlap with SDSS equatorial Stripe 82 for calibration (200 sq deg) Connector region (800 sq deg) J. Annis Total Area: 5000 sq deg Limiting Magnitudes – Galaxies: 10σ grizy = 24.6, 24.1, 24.3, 23.8, 21.8 – Point sources: 5σ grizy = 26.1, 25.6, 25.8, 25.3, 23.3 Observation Strategy – 100 sec exposures – 2 filters per pointing (typically) – gr in dark time (moon down) – izy in bright time (moon up) – Multiple tilings/overlaps to optimize photometric calibrations – 2 survey tilings/filter/year – All-sky photometric accuracy – Requirement: 2% – Goal: 1%

27 I.Galaxy Cluster counts vs. redshift –20,000 clusters to z=1 with M > 2x10 14 M sun II.Weak lensing –300 million galaxies with shape measurements over 5000 sq deg III.Baryonic Acoustic Oscillations / Galaxy Clustering –300 million galaxies to z = 1 and beyond IV.Supernovae as Standard Candles –1900 SNe Ia, z = DES’s Four Probes of Dark Energy Growth of Structure (+Geometry/Volume) Growth of Structure Also for calibration of cluster masses for cluster counting Standard Ruler (the “bump” in the power spectrum seen in the Cosmic Microwave Background, but at z = 0 – 1) Standard Candle

28 Forecast DES Constraints on Dark Energy Equation of State Note: a = R / R 0 = 1 / (1 + z) DES Goal: Reduce area of red oval by a factor of ~4 from current dark energy experiments

29 What are the Characteristics of the Dark Energy Camera (DECam)?

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

31 DECam CCDs and Focal Plane 62 2k x 4k image CCDs 520 Mpix 0.27 arcsec/pixel (15-micron pixels) FOV: 2.2º (3 sq deg) LBL design – fully depleted, 250-micron thick CCDs – 17 second readout time – QE> 50% at 1000 nm DES Focal Plane: The Hex B. Flaugher DES CCD QE Current Mosaic II QE

32 DECam Optics UK, Michigan, FNAL C1 C2 - C3 C4 C5, vacuum window Filters & Shutter Focal plane Bipods Attachment ring C1

33 Filter Changer - UMichigan Capacity for 8 filters. Filter diameter: 620 mm. Filter thickness: ~13mm DES g,r,i,z,y filters Community filters: u-band very likely. Others?

34 Some Tests of the CCDs and the Front-End Electronics Imager Prototype/Multi-CCD Test Vessel FNAL and UChicago CTIO-1m + DECam 2kx2k CCD April 2008 CTIO-1m + DECam 2kx2k CCD Oct 2008 (credit: J. Estrada)

35 Community Use of DECam

36 Epilogue Mentioned only Dark Energy but the DES is very similar to the SDSS imaging survey (grizy vs. ugriz) but deeper! (r to 24 instead of r to 22) Like with SDSS, can do: – Quasars – Galaxy environments – Superclusters – Stellar streams associated with Milky Way –...

37 visualization: David W. Hogg (NYU) with help from Blanton, Finkbeiner, Padmanabhan, Schlegel, Wherry data: Sloan Digital Sky Survey and the Bright Star Catalog The Power of Large Imaging Surveys

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50 Extra Slides

51 Hubble Diagram

52 CMB Maps

53 I.Galaxy Cluster counting –20,000 clusters to z=1 with M > 2x10 14 M sun II.Weak lensing –300 million galaxies with shape measurements over 5000 sq deg III.Baryonic Acoustic Oscillations / Galaxy Clustering –300 million galaxies to z = 1 and beyond IV.SNe as Standard Candles –1900 SNe Ia, z = Survey Area Overlap with South Pole Telescope Survey (4000 sq deg) Overlap with SDSS equatorial Stripe 82 for calibration (200 sq deg) Connector region (800 sq deg) J. Annis Total Area: 5000 sq deg DES’s Four Probes of Dark Energy

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55 Photometric Redshifts Measure relative flux in five filters grizy: track the 4000 A break Estimate individual galaxy redshifts with accuracy  (z) < 0.1 (~0.02 for clusters) Precision is sufficient for Dark Energy probes, provided error distributions well measured. Note: good detector response in z band filter needed to reach z>1 Elliptical galaxy spectrum ( + JHK data from VISTA Hemispheric Survey )

56 I. DES Galaxy Clusters Galaxy cluster abundance, mass function, and correlations sensitive to cosmology via effects on volume and on growth rate of perturbations Complementary cluster samples DES optical data provide accurate cluster photometric redshifts South Pole Telescope (SPT) Sunyaev-Zel’dovich effect (SZE) data provides robust cluster masses Tens of thousands of clusters in 4000 deg 2 area of DES-SPT overlap out to z=1 Multiple cluster mass estimators (optical richness, SZE, weak lensing) and cross-checks of sample selection effects Mohr Volume Growth Number of clusters above observable mass threshold Dark Energy equation of state M > 2x10 14 M sun

57 Cluster Cosmology with DES 3 Techniques for Cluster Selection and Mass Estimation: Optical galaxy concentration Weak Lensing Sunyaev-Zel’dovich effect (SZE) Cross-compare these techniques to reduce systematic errors Additional cross-checks: shape of mass function; cluster correlations

58 DES photometric redshifts accurate to dz~0.02 for clusters out to z~1.3 z=0.041 z=0.138 z=0.277 z=0.377 Examples from SDSS Clusters in the Optical

59 Clusters from the Sunyaez-Zeldovich Effect: Synergy with the South Pole Telescope Credit: L. Van SpeybroekSunyaev & Zeldovich (1980) The South Pole Telescope John Carlstrom (PI) 10m submm telescope 150 & ~250 GHz 1000 element bolometer array 4000 sq. deg. survey Southern Galactic cap measures cluster masses using SZ effect First Light: 16 February 2007

60 Finding Clusters with the SZE Credit: Carlstrom et al. (2002) Pros: – can identify galaxy clusters nearly independent of redshift z=0.17 z=0.55 z=0.83 z=0.89 z=0.55 z=0.25

61 Finding Clusters with the SZE Credit: Carlstrom et al. (2002) Pros: – can identify galaxy clusters nearly independent of redshift z=0.17 z=0.55 z=0.83 z=0.89 z=0.55 z=0.25 Cons: – can identify galaxy clusters nearly independent of redshift

62 Observer Dark matter halos Background sources Statistical measure of shear pattern, ~1% distortion Radial distances depend on geometry of Universe Foreground mass distribution depends on growth of structure II. DES Weak Lensing & Cosmic Shear

63 Weak Lensing of Faint Galaxies: distortion of shapes Background Source shape

64 Weak Lensing of Faint Galaxies: distortion of shapes Foreground Cluster Background Source shape Note: the effect has been greatly exaggerated here

65 Lensing of real (elliptically shaped) galaxies Foreground Cluster Coadd signal around a number of clusters Background Source shape

66 Mapping the Dark Matter in a Cluster of Galaxies via WeakGravitational Lensing Data from Blanco 4-meter at CTIO Joffre et al.

67 Cosmic Shear Angular Power Spectrum in 4 Photo-z Slices Shapes of ~300 million galaxies, median redshift  z  = 0.7 Primary Systematics: photo-z’s, PSF anisotropy, shear calibration Weak Lensing Tomography DES WL forecasts conservatively assume 0.9” PSF = median delivered to existing Blanco camera: DECam should do better & be more stable Huterer Statistical errors shown

68 Weak Lensing Tomography Huterer Statistical errors shown Cosmic Shear Angular Power Spectrum as a function of redshift Shapes of ~300 million galaxies Median redshift = redshift bins

69 CMB Angular Power Spectrum SDSS galaxy correlation function Acoustic series in P(k) becomes a single peak in  (r) Eisenstein et al CMB Angular Power Spectrum III.DES Baryonic Acoustic Oscillations (BAO) Cosmic Microwave Background (z~1000) Luminous Red Galaxies from SDSS (z~0.35)

70 Baryon Acoustic Oscillations: CMB & Galaxies CMB Angular Power Spectrum SDSS galaxy correlation function Acoustic series in P(k) becomes a single peak in  (r) Eisenstein et al CMB Angular Power Spectrum

71 Measuring BAO vs. Redshift in DES Wiggles due to BAO Blake & BridleFosalba & Gaztanaga

72 Credit: Will Percival III.Baryonic Acoustic Oscillations (BAO): Galaxy Angular Power Spectrum in the DES

73 IV. DES Supernovae Geometric Probe of Dark Energy (brightness vs. redshift) Repeat observations of 5 fields –CDF-S, SDSS Stripe 82, SNLS D1/Virmos, XMM-LSS, ELIAS S1 –all are within DES wide-area survey footprint) –2 deep fields (10 min in g, 20 min r, 30 min i, 50 min z), 3 shallower Mean cadence of ~5 days Mixture of photometric and non-photometric time (10% of survey time) ~ 1900 well-measured SN Ia lightcurves, 0.25 < z < 0.75 SDSS

74 DES Filters Wavelength [Å] Transmission, Rel. Photon Flux G191-B2B grizY DES grizy filters are being manufactured by Asahi, Japan Filters are large, 620 mm in diameter Care has been taken to specify spatial uniformity requirements on filter transmission vs. wavelength, in order to meet our 2% photometric calibration requirement

75 Forecast Constraints DES+Stage II combined = Factor 4.6 improvement over Stage II combined Consistent with DETF range for Stage III DES-like project Large uncertainties in systematics remain, but FoM is robust to uncertainties in any one probe, and we haven’t made use of all the information DETF FoM

76 Survey Power (approximate) Telescope Mirror Diameter (meters) Field of View (deg 2 ) A  SDSS CFHT PanSTARRS 1 PanSTARRS x x DES4330 LSST Partial Source: Pan-STARRS Website