# Presentation: 302236

## Dark Energy Survey Science Proposal

- Josh Frieman

- http://astro.uchicago.edu/~frieman/DES/proposal/proposal.pdf

## Context: Dark Energy Task Force (DETF) Report

-  Recognized 4 promising Dark Energy probes familiar to DES
-  Defined Figure of Merit (FoM) for Dark Energy experiments
-  Envisioned staged approach to DE based on FoM & scale:
-      Stage III: near-term, intermediate-scale projects; FoM~3-5
-      Stage IV: longer-term, large-scale: LST, JDEM, SKA; FoM~5-10
-  Recommended immediate start to a Stage III project
-  Considered 8 `generic’ Stage III projects, 6 of them essentially identical to DES
-  Proposal should make the case that DES satisfies requirements for a DETF Stage III project, and that multiplicity of methods & control of systematics should yield results toward optimistic end of the Stage III FoM.

## Science Proposal Team

- Clusters: Mike Gladders, Tim McKay
- Weak Lensing: Bhuv Jain, Sarah Bridle
- Supernovae:** **Bob Nichol, Masao Sako, w/input from Gajus Miknaitis, Ramon Miquel, Rick Kessler
- BAO: Will Percival, Enrique Gaztanaga, Wayne Hu
- Other DE Probes: Scott Dodelson
- Simulations: Gus Evrard, Paul Ricker, Andrey Kravtsov
- Photo-z’s: Huan Lin, Ofer Lahav
- Fisher Matrix Mavens: Wayne Hu, Gary Bernstein, Jochen Weller, Scott Dodelson, Zhaoming Ma
- Reviewers: Joe Mohr, Ramon Miquel, Chris Smith, Gary & Rebecca Bernstein, David Weinberg
- building on NOAO Proposal (2004) and DETF White Papers (2005)

## Schedule

- Oct. 18: letter from DOE & NSF
- Late Oct: Science proposal team formed
- Phone meetings: 11/3, 11/10, 11/17, 11/28, 12/7
- First drafts compiled ~11/27
- Revised drafts sent to reviewers 12/2
- Reviews received 12/6
- Final sections due 12/11 PM
- Completed science section delivery 12/13
- Proposal submission 12/20

## DES Forecasts: Power of Multiple Techniques

*                                     *

-   Ma, Weller,
-   Huterer, etal

- Assumptions:
- Clusters: SPT-selected,
- 8=0.75, zmax=1.5,
- WL mass calibration
- (*no* clustering self-calibration)
- BAO: lmax=300
- WL: lmax=1000
- (*no* bispectrum or galaxy-shear)
- 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

## I. Clusters and Dark Energy

- Requirements
- Understand formation of dark matter halos
- Cleanly select massive dark matter halos (galaxy clusters) over a range of redshifts
- Redshift estimates for each cluster
- Observable proxy that can be used as cluster mass estimate:
-         *g(O|M,z)**  *
- Primary systematics:
- Uncertainty in *g** *(bias & scatter)
- Uncertainty in *O* selection fn.

## 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 (self-calibration)

## Statistical Weak Lensing Calibrates

- Cluster Mass vs. Observable Relation

-                           Hansen etal                                      Johnston, Sheldon, etal, in preparation

## SZE vs. Cluster Mass: Progress in Simulations

- Integrated SZE flux decrement depends only on cluster mass: insensitive to details of gas dynamics/galaxy formation in the cluster core          robust scaling relations

- Nagai

- SZE flux

****** ****Adiabatic**
**∆**** ****Cooling+Star**
**   ****Formation**

- small (~10%)
- scatter

## II. Weak Lensing: Cosmic Shear

- 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

**Notes:**
Cosmic Web – bottom up scenario – clusters then filaments then walls (membranes).
Note that filaments not well traced by galaxies & too ephemeral to emit x-rays, so lensing only way to detect.

##   Weak Lensing Tomography

- Cosmic Shear
-  Angular Power
-  Spectrum in
-  Photo-z Slices
- Shapes of ~300
-   million galaxies
-   median redshift z = 0.7
- Primary Systematics:
-   photo-z’s, PSF anisotropy,
-   shear calibration, intrinsic
-   alignments

-   Weak Lensing Tomography

- DES WL forecasts conservatively assume 0.9” PSF = median *delivered* to
- existing Blanco camera: DES should do better & be more stable

- Huterer

- Statistical errors
- shown

##             Reducing WL Shear Systematics

- DECam+Blanco
- hardware
- improvements that
- will reduce raw
- PSF anisotropy
- Include
- Bispectrum and
- Galaxy-shear:
- robustness
- against systematics

- Red: expected signal

- Results from
- 75 sq. deg. WL
- Survey with
- Mosaic II and BTC
- on the Blanco 4-m
- Bernstein, etal
- DES: comparable
- depth: source
- galaxies well
- resolved & bright:
- _low-risk_

- (improved systematic)

- (signal)

- Shear systematics should be under control at level needed for DES

- (old systematic)

- Cosmic Shear

##  III. Supernovae

- Strawman Strategy: Repeat observations in *riz* of 40 deg2
-      `wide & shallow’:
-      ~2600 well-measured SN Ia
-       lightcurves, 0.05 < z < 0.8
- Alternative Strategy: `Deep & narrow’ *riz* of 9 deg2, spectroscopic follow-up concentrated on Ia’s in ellipticals (lower extinction, better photo-z’s):
-      ~200+800 Ia’s to z~1
- Larger sample, improved *z*-band response compared to ESSENCE, SNLS
- Issue: what fraction spectroscopic follow-up for distances & sample purity

## IV. Baryon Acoustic Oscillations & Large-scale Structure

- IV. Baryon Acoustic Oscillations & Large-scale Structure

- CMB
- Angular
- Power
- Spectrum

- SDSS galaxy
- correlation function

- Acoustic series in *P*(*k*) becomes a single peak in **(*r*)

- Bennett, etal

- Eisenstein etal

## BAO in DES: Galaxy Angular Power Spectrum 

- Probe substantially larger volume and redshift range than SDSS
- Systematics:
- photo-z’s, photometric errors,
- Non-linearity,
- Scale-dependent bias
- Controls:
- Calibration, bispectrum

- Wiggles due
- to BAO

## Photometric Redshifts

- • Measure relative flux in
-   four filters *griz*:
-   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

## Spectroscopic Redshift 

- Spectroscopic Redshift
- Training Sets for DES

| Redshift Survey | Number of Redshifts Overlapping DES |
| --- | --- |
| Sloan Digital Sky Survey | 
70,000, r < 20
 |
| 2dF Galaxy Redshift Survey | 90,000, bJ<19.45 |
| VIMOS VLT Deep Survey | ~60,000, IAB<24 |
| DEEP2 Redshift Survey | ~30,000, RAB<24.1 |

- _Training Sets to the DES photometric depth in place_
-  (advantage of a `relatively’ shallow survey)

## DES Cluster Photometric Redshifts: 

- DES Cluster Photometric Redshifts:
-       Simulations & SDSS Results

## Galaxy Photo-z Simulations

- DES
- griz filters

- 10 Limiting Magnitudes
-   g	24.6
-   r	24.1
-   i	24.0
-   z	23.9
- +2% photometric calibration
- error added in quadrature
- Key: Photo-z systematic errors
- under control using *existing*
- spectroscopic training sets to
- DES photometric depth: low-risk

- +VHS JK

- Improved Photo-z & Error Estimates and robust methods of outlier rejection

- DES

- Cunha, etal

- DES + VHS on
- ESO VISTA 4-m
- enhances science reach

- +Y

- Variance and Bias of Photo-z Estimates

- Cunha etal

- Variance

- Bias

## Weak Lensing & Photo-z Systematics

- Ma

- (w0)/(w0|pz fixed)

- (wa)/(wa|pz fixed)

## BAO & Photo-z Systematics

- Ma

- (w0)/(w0|pz fixed)

- (wa)/(wa|pz fixed)

## DES and the Dark Energy Program

- Survey strategy delivers substantial DE science after 2 years
- Relatively modest, low-risk, near-term project with high discovery potential
- Scientific and technical precursor to the more ambitious Stage IV  Dark Energy projects to follow: LSST and JDEM
- DES in unique international position to synergize with SPT and VISTA on the DETF Stage III timescale