# Presentation: 486676

##      Dark Energy Experiments: DES and Beyond

-      Dark Energy Experiments: DES and Beyond

- Tim McKay
- University of Michigan

- Presented for the Dark Energy Survey Collaboration

## Why Dark Energy?

- GR provides our theory for cosmic evolution: spacetime evolution driven by contents according to Einstein Eqs
- During the 1990s, the first precise cosmological measurements emerged
- CMBR (COBE & WMAP)
- Large scale structure (2DF, SDSS)
- High Redshift Supernovae (SCP & High-z)

- These are all consistent with a flat FRW universe, but *only *if it is dark dominated: with DM~0.25 and  ~0.7
- Extensive evidence for dark matter already existed independent of the large scale metric
- Observations of accelerated expansion are so far consistent with a cosmological constant

## The Goal of DE Experiments

- The goal of all DE experiments is to further test this consistency
- Are all aspects of the Universe we can observe consistent with this simple model, or do they contain hints of complications?

- Cosmic evolution takes place on many scales!
- On the largest scales only average energy densities matter: the overall metric
- Small scales: local matter density is high: expansion ceases and metric stabilizes
- On intermediate scales DE and DM compete

- Z=27.4

- Z=0

## Dark Energy Task Force

- Established by AAAC and HEPAP as joint subcommittee to advise the 3 agencies: Report issued in September 2006 (astro-ph/0609591)
- ``Strongly recommend...an aggressive program to explore dark energy”
- Defined stages of projects:
- Stage I=completed
- Stage II=on-going
- Stage III=near-term, medium-cost, proposed: _improve constraints by 3-5x_
- Stage IV=LSST, SKA, JDEM: _improve constraints by 10x_
- Considered 4 main techniques to study DE and ``Recommend that the...program have multiple techniques at every stage”
- Stage III experiments will also refine methods for Stage IV
- _Recommend immediate start of Stage III__ _

## Observational approaches

- Type-Ia Supernovae
- Absolute brightness estimated independent of apparent brightness
- Tests geometry through the luminosity redshift relation
- Gravitational lensing
- Clustered matter distorts images of background objects
- Tests growth of structure and geometry through the angular diameter redshift relation

- Baryon acoustic oscillations
- Sound horizon scale at recombination imprinted on large scale structure
- Angular diameter redshift relation
- Galaxy clusters
- Largest peaks in the density distribution
- Tests growth of structure and geometry through the evolution of volume

- All aim to measure expansion and what happens within it...

## The Dark Energy Survey

- Blanco 4-meter at CTIO

- *in systematics & in cosmological parameter degeneracies
- *geometric+structure growth: test Dark Energy vs. Gravity

- CTIO 4m Telescope

**A study of dark energy using four independent and complementary********* techniques**
- Galaxy cluster surveys
- Weak lensing
- Galaxy angular power spectrum
- SN Ia distances
**Two linked, multiband optical surveys**
- 5000 deg2 *gri *and *z  *(or Y+Z?)
- Repeated observations of 40 deg2
**Construction and Science**
- Build new 3 deg2 camera for Blanco 4m in Chile (FNAL)
- Invest in upgrades for the telescope (NOAO)
- Build DM system to archive and process data at NCSA
- Survey and Science: 2010-2015

## Institutions Participating in the DES Collaboration

**Fermilab**
**Argonne National Laboratory**
**Lawrence Berkeley National Laboratory**
**NOAO/CTIO**
**University of Illinois at Urbana-Champaign**
**University of Chicago**
**University of Michigan**
**The University of Pennsylvania**
**The Ohio State University**
**Spain-DES Collaboration:**
- 	Institut d'Estudis Espacials de Catalunya (IEEC/ICE), 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
**Brazil-DES Consortium**
- 			*17 institutions and 110 participants*

## The DES Instrument: DECam

- 3.6 m

- 1.6 m

- Hexapod

- Optical
- Lenses

- Readout
- for > 70 CCDs

- Filters
- Shutter

## DES and the South Pole Telescope

- DES will survey the same southern region of sky as the NSF funded “South Pole Telescope”
- SPT will make microwave maps of 4000 sq degrees of the DES survey region
- Allows independent measurement of clusters through the SZ effect
- This unique combination is a key feature of DES

- SPT first light achieved in Feb. 2007

- Cluster science will be a focus for DES

## Clusters in theory

**Peaks in the dark matter density field**
- Large scale features, (counts and clustering), robustly predicted within any cosmological model
- Internal structure and evolution of baryons is less well determined

- Dark matter distribution

- Virgo consortium HV simulations

## Example predictions

**n(M,z=0)**

**n(M>M****lim****,z)**

- Examples of the rich array of cluster properties simulations can predict

## Observing clusters

- Many luminous galaxies (~2% of mass: 10% of baryons)
- BCG and red sequence
- Additional galaxies
- Intracluster stars
- Hot gas (~18% of mass: 90% of baryons)
- Emits X-rays
- Causes SZ decrement in microwave background
- Dark matter clump (~80% of mass)
- Causes distortion of background sources

- Cluster of galaxies

- SZ decrement

- Carlstrom et al. 2002

- Each of these signatures can be used for cluster detection and measurement.
- None measure quite what theory predicts...

## Photometric optical cluster detection

- Member galaxies tightly clustered in space and color: NFW profile and E/S0 ridgeline

- Uniformly old stellar populations allow tight mapping between color and redshift; present to z=1.5

- High S/N detection of individual galaxies allows detection of objects down to small group scales

## For every cluster, we measure position, a “richness” Ngal, the distance zphoto, and a variety of structural parameters. 

- Optical cluster finding: example color cluster images from the SDSS

- For every cluster, we measure position, a “richness” Ngal, the distance zphoto, and a variety of structural parameters.

**Notes:**
These images from the SDSS illustrate the point. Cluster galaxies have remarkably uniform colors, colors which change strongly with redshift, allowing accurate 3D cluster identification. Clusters at higher redshift are obviously redder and smaller than those at low redshift. In fact with a bit of practice, you can estimate cluster redshifts by eye very well.

## How well can optical selection do?

- Large optically selected catalogs already exist
- SDSS maxBCG: ~14,000 clusters, z=0.1-0.3 (Koester et al., Rozo et al. 2007)
- RCS & RCS-II: ~450 clusters, z=0.5-1.2 (Gladders & Yee, 2005)

- Precise redshift estimates for clusters. Distances to better than 5%.
- Highly complete and pure samples (both > 90%).

- Approximately volume limited catalogs can be constructed

## How to measure the mass-observable relation?

- Weak lensing measurements of the cluster-mass correlation function calibrate the mass-observable relation

- The cluster-mass correlation function can be non-parametrically inverted to obtain the mass profile (Johnston et al. 2006)
- _Key feature_: the same data used to detect the clusters is used for the lensing measurements
- Profiles provide tests of halo structure and halo clustering

## Progress in simulations 

- Progress in simulations

## Connecting theory and observation

- To do cosmology, we must connect what we predict what we measure *precisely*
- We measure many things:
- The cluster number function N(Ngal, zphoto)
- The cluster clustering (Ngal,zphoto,r┴)
- Scaling relations for other observables: SZ(Ngal,zphoto), lens (Ngal,zphoto ,r ┴) and gal(Ngals ,zphoto,r ┴)

- To predict these, we need to understand how galaxies occupy dark matter halos
- This theory/observation gap is closing from both sides:
- Richer observations (counts, lensing, dynamics, x-rays, SZ, clustering)
- More detailed simulations: (sub-halo resolution, gas dynamics, galaxy formation)
- Joining _***all of these***_ allows model constraints to be precise and well tested

## geometric+
growth

*                                     *

-   Ma, Weller, Huterer, etal

- Assumptions:
- Clusters:
- 8=0.75, zmax=1.5,
- WL mass calibration
- (no clustering)
- BAO: lmax=300
- WL: lmax=1000
- (no bispectrum)
- Statistical+photo-z
- systematic errors only
- Spatial curvature, galaxy bias
- marginalized
- Planck CMB prior

*w*(*z*)* =w**0**+w**a*(1*–a*)           68% CL

- geometric

- geometric+
- growth

- Clusters
- if 8=0.9

- DETF Figure of
- Merit: inverse
- area of ellipse

- DES Forecasts: Power of Multiple Techniques

## Status of the DES

- DOE and NSF have reached a formal agreement on how to jointly review the project
- Review held May 1-3, 2007 at Fermilab
- Draft report from this review panel recommends CD-1 to DOE and NSF

- Van Citters and Staffin have enabled the creation of a Joint Oversight Group (JOG) in response to the draft report
- CD-1 on hold until certain issues Data Management and the connections between Fermilab, NCSA, and NOAO issues resolved

## DES Schedule Goals

- September 2009: DECam maintenance facility at CTIO
- January 2010: New Telescope Controls System on the Blanco
- April 2010: Commission the DES DM at NCSA and transfer simulated data through the DTS to NCSA.
- April 2010: Deliver a partial SISPI system to CTIO and begin the integration of SISPI with the telescope controls system, the DTS, and the DES DM system.
- July 2010: Deliver DECam to CTIO.
- July 2010: Deliver the Optical Corrector to CTIO.
- Complete commissioning and make the first science observations while the South Galactic Cap is visible between September 2010 and March 2011.

## Conclusions

- DES observations will provide great statistical power and sensitivity
- Systematic uncertainty in the connection of observation to theory is the primary challenge for modern cosmology
- New simulations and measurements substantially reduce this uncertainty

- Major advances are being made now, in large part by members of the DES project team working with existing SDSS data and simulations
- DES + SPT will provide unique new constraints on this connection and will bring the promise of cluster cosmology to fruition

## One Survey: Three Projects

- 	*The Collaboration proposes to organize the construction of DES as three projects:*
- Fermilab leads the construction of DECam, the survey instrument.
- NCSA/UIUC leads the development and deployment of the DES Data Management System.
- CTIO leads the construction of the facilities improvements at CTIO and  the integration of DECam on the Blanco
- All collaboration members contribute to each of these projects as well as to science analysis