Precision Studies of Dark Energy with the Large Synoptic Survey Telescope

David L. BurkeSLAC

for the

LSST Collaboration

Rencontres de MoriondContents and Structures of the Universe

The LSST Collaboration

Brookhaven National Laboratory

Harvard-Smithsonian Center for Astrophysics

Johns Hopkins University

Las Cumbres Observatory

Lawrence Livermore National Laboratory

National Optical Astronomy Observatory

Ohio State University

Pennsylvania State University

Research Corporation

Stanford Linear Accelerator Center

Stanford University

University of Arizona

University of California, Davis

University of Illinois

University of Pennsylvania

University of Washington

Outline

• The LSST Mission

• The LSST Telescope and Camera

• Dark Energy Science

• Schedule and Plans

The LSST Mission

Photometric survey of half the sky ( 20,000 square degrees).

Multi-epoch data set with return to each point on the sky approximately every 3 nights for up to 10 years.

Prompt alerts (within 60 seconds of detection) of transients to observing community.

Fully open source and data.

Deliverables

Archive 3 billion galaxies with photometric redshifts to z = 3.

Detect 250,000 Type 1a supernovae per year (with photo-z < 1).

LSST Performance Specifications

Cadence of two 15 second exposures with 2 second read-out followed by 5 second slew (open-loop active optics) to new (nearby) pointing.

FOV = 3.5 degrees diameter.

Single-exposure Depth = 24.5 AB mag. (r-band)

Stacked (300-400 exposures) Depth = 27.8 AB mag. (r-band)

Median Image PSF (FWHM) = 0.7 arc-sec.

Broad-band (ugrizy; 350nm-1050nm) internal photometric accuracy of 0.010 mag (zero-point across the sky).

Relative astrometric accuracy of 10 mas.

Fast, Wide, Deep, and Precise

Telescope and Camera

8.4m Primary-TertiaryMonolithic Mirror

3.5° Photometric Camera

3.4m Secondary Meniscus Mirror

Telescope Optics

Polychromatic diffraction energy collection

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 80 160 240 320

Detector position ( mm )

Imag

e di

amet

er (

arc-

sec

)

U 80% G 80% R 80% I 80% Z 80% Y 80%

U 50% G 50% R 50% I 50% Z 50% Y 50%

PSF controlled over full FOV.

Paul-Baker Three-Mirror Optics

8.4 meter primary aperture.

3.5° FOV with f/1.23 beam and 0.20” plate scale.

Similar Optical Mirrors and Systems

Large Binocular Telescope

f/1.1 optics with two 8.4m primary mirrors.

SOAR 4.2m meniscus primary mirror

Camera

Filters andShutter

Refractive Optics

Focal Plane Array (at 153 K)

Cryostat

~ 2m

Focal Plane Array (FPA)

Shack-Hartmann Wavefront Sensors and

Fast Guide Sensors

3.5° Field of View (634 mm diameter)

Pixels: 3.2 109 on 10 m pitch.

Plate Scale: 0.200 arc-sec.

FPA Flatness: 10 m peak-valley.

“Raft” of nine 4k4k CCDs

Survey Power

0

40

80

120

160

200

240

280

320

Ete

nd

ue

(m

2 de

g2 )

LSST PS4 PS1 Subaru CFHT SDSS MMT DES 4m VST VISTAIR

SNAPOpt+IR

Multi-Epoch Data Archive

Average down instrumental and atmospheric statistical variations.

Large dataset allows systematic errors to be

addressed by subdivision.

Multi-Epoch Data Archive

Average down instrumental and atmospheric statistical variations.

Large dataset allows systematic errors to be

addressed by subdivision.

LSST Dark Energy Highlights

o Weak lensing of galaxies to z = 3. Two and three-point shear correlations in linear and non-linear

gravitational regimes.

o Supernovae to z = 1. Discovery of lensed supernovae and measurement of time delays.

o Galaxies and cluster number densities as function of z. Power spectra on very large scales k ~ 10-3 h Mpc-1.

o Baryon acoustic oscillations. Power spectra on scales k ~ 10-1 h Mpc-1.

Disclosure and Agreement

Unless stated otherwise, error forecasts are not marginalized over unspecified parameters.

Generally, flat-space ΛCDM values are assumed for unspecified parameters.

Do you accept the terms and conditions of this agreement?

I accept.

I do not accept.

DLS

DS

= 4GM/bc2

Impact Parameter b

4GM/bc2

Sheared Image

Shear

Gravity & Cosmology change the growth rate of mass structure.

Cosmology changes geometric distance factors.

DLS

DS

Weak Lensing Geometry

Shear Power Spectra Tomography

LSST expects well below 0.001 in residual shear error ….

0.01

0.001

Ne

ede

d S

he

ar Se

nsitivity

Linear regime Non-linear regime

ΛCDM

Measure• Shear spatial auto-correlation binned in z.• Cross correlations between different bins in z.

Differing sensitivities to cosmology and gravity.

<shear> <shear> = 0.07= 0.07

<shear> <shear> = 0.000013= 0.000013

Raw De-trailed PSF Corrected

13 a

rcm

in

(l =

40)

<shear> = 0.04

<shear> = 0.000007

Single 10 sec exposure in 0.65 arcsec seeing.

Weak Lensing Through the AtmosphereData from Prime-Cam on 8-m Subaru

LSST Goal: Residual shear 0.0001.

Train on random half of the stars; measure residual shear on other half.

Residual 2-Point Shear Correlations

ΛCDM shear signal

Typical separation of reference stars in LSST exposures.

LSST multi-epoch survey provides sensitivity well below target signal.

Photometric Redshifts and Weak Lensing

Contours of constant error in w and wa as functions of statistical and systematic photo-z errors. Ma, Hu, Huterer (2005)

Need to know bias and resolution in z with good accuracy. LSST goal …

zbias 0.002 (1 + z)

Z 0.003 (1 + z)

… will match systematic errors in cosmological parameters to statistical errors for z 3 .

Photo-z Calibration Campaign

Together with angular correlations of galaxies, this training set enables LSST 6-band photo-z error calibration to better than required for LSST statistics limit precision cosmology

• Transfer fields - 200,000 galaxies with 12-band photo-z redshifts.

• Calibrate 12-band photo-z with subset of 20,000 spectroscopic redshifts.

Simulation of 6-band photo-z distribution for LSST dataset.

Simulation of 12-band photo-z calibration field at 26 AB mag.

Need to calibrate transfer photo-z to 10% accuracy to reach desired precision

z 0.05 (1+z) z 0.03 (1+z)

Simulated light curves from the LSST deep field survey.

Simulated Hubble diagram from 30,000 supernovae detected over three years of observing in the LSST deep-field survey.

Studies of Supernovae with LSST

LSST Supernovae Data Sets

Survey cadence will detect 250,000 supernovae per year (to z 0.8), and provide photometry every three days in rotating colors (primarily r, i, and z).

Nightly deep-field survey will detect and follow supernovae to z 1.2.

z = 0.8

photo-z

Weak Lensing and SNe-Ia Forecasts

Combined

JDEM SNe

LSST WL

Principal component analysis [Huterer and Starkman (2003)] of expected sensitivity to

dark energy equation of state.

Combination of distance measurements from SNe with parameters from weak lensing ….

Complementary probes of cosmology and gravity.

w

wa

RS~140 Mpc

Standard Ruler

Two Dimensions on the Sky Angular Diameter Distances

Three Dimensions in Space-Time Hubble Parameter

Baryon Acoustic Oscillations (BAO)

CMB BAO

Baryon-DM Gravitational Effects

Mode CouplingClustering In-Fall

Velocity Dispersion along Line-of-Sight

BAO Power Spectra

Two-dimensions on the sky.3 billion galaxies.

Combination yields accuracy 2 % on w0.<~

Three-Dimensional BAO and Hubble

Suppression of line-of-sight modes by photo-z errors.

2223

2 /exp Hkc zPphoto-z(k,μ) = Pz(k,μ)

Present error on H.

Accuracy needed for LSST WL and SNe.

May do better. We will see.

LSST Project Milestonesand Schedule

2006 Site SelectionConstruction Proposals (NSF and DOE).

2007-2008 Complete Engineering and DesignLong-Lead Procurements

2009-2012 Construction and First Light

2013 Commissioning

LSST Site Selection – Two Proposals

Final Selection – 14 April 2006

San Pedro Mártir Cerro Pachón

Summary

• The LSST will be a significant step in survey capability.

Optical throughput ~ 100 times that of any existing facility.

• The LSST is designed to control systematic errors.

We know how to make precise observations from the ground.

We know how to accurately calibrate photo-z measurements.

Multi-epoch with rapid return to each field on the sky – advantages

likely not yet fully appreciated.

• The LSST will enable multiple simultaneous studies of dark energy.

Complementary measurements to address degeneracy andtheoretical uncertainty in a single survey.

• The LSST technology is ready.