The LSST andExperimental Cosmology at KIPAC

David L. BurkeSLAC/KIPAC

SLAC HEP SeminarOctober 31, 2006

Outline

• Experimental Cosmology

• Gravitational Lensing

• KIPAC Activities

• The Large Synoptic Survey Telescope

Elements of Cosmology

Space and Time

The Big Bang and inflation.

Homogeneous, isotropic, expanding universe.

Matter and Energy

Particles and quantum interactions.

Mass and General Relativity.

What we see in the laboratory. What we see

in the sky.

What We See in the Sky

3000 1080 ~15 0Redshift z =

The Expanding Universe

Hubble 1929-1934

Isotropic linear distance-velocity relation,

“Hubble Parameter” H0.

Perlmutter/Reiss 1998

Non-linear distance-redshift relation,

Dark Energy and the Cosmological Constant

Z = 0 21

Matter in the Universe

Geller/Huchra 1989Large Scale Structure

Rubin/Ford 1980Galaxy Rotation Curves

Dark Matter and Evolution of Structure

The “Great Wall”

Cosmic Microwave Background

Penzias/Wilson 1964 Mather/Smoot 1992 Wilkison 2006

Best FitCDMSeeds fertilized by

cold dark matter grow into large scale structure.

“CDM Model”

Concordance and Discord

Is the universe really flat?

What is the dark matter? Is it just one thing?

What is driving the acceleration of the universe?

What is inflation?

Can general relativity be reconciled with quantum mechanics?

Experimental Cosmology

CMB and Baryon Oscillations – dA(z) and H(z).

Supernovae – dL(z).

Galaxies and clusters – dA(z), H(z), and Cl(z).

Gravitational lensing – dA(z) and Cl(z).

Elements of General Relativity(Sean Carroll, SSI2005, http://pancake.uchicago.edu/~carroll/notes )

[Geodesic Equation] [Einstein Equation]

The metric g, that defines transformation of distances in coordinate space to the

distances in physical space we can measure, must satisfy these equations.

Homogeneous, isotropic, flat, expanding universe:

g = -1 0 0 00 a(t) 0 0

0 0 a(t) 0 0 0 0 a(t)

More generally:Curvature of space.

“Size” of space relative to time.Gravitational potential (weak)

d2 = dt2 – a2(t) · dx2

E = 1.74 arc-sec

Newton, Einstein, and Eddington

Soldner 1801

Einstein 1915

Eddington 1919 “between 1.59 and 1.86 arc-sec”

Propagation of Light Rays

There can be several (or even an infinite number of) geodesics along which light travels from the source to the observer.

Displaced and distorted images.

Multiple images.

Time delays in appearances of images.

Observables are sensitive to cosmic distances and to the structure of energy and matter (near) line-of-sight.

A complete Einstein ring.

Strong Lensing

Galaxy at z =1.7 multiply imaged by a cluster at z = 0.4.

Multiply imaged quasar (with time delays).

Propagation of a Bundle of Light

Central Ray0

ξi

ξj

ξ ( )

Bundle of rays each labeled by angle with respect to the central ray as they pass an observer at the origin.

Linear approximation,

and = 0 case,

ξ () = D ()

D () = dA()

angular diameter distance

2-dimensional vector

Weak Lensing Approximation

If distances are large compared to region of significant gravitational potential , the deflection of a ray can be localized to a plane – the “Born” approximation.

Unless the source, the lens, and the observer are tightly aligned (Schwarzschild radius), the deflection will be small,

And the actual position of the source can be linearly related to the image position,

(Einstein)

Distorted Image

Source

ξi

ξj

Convergence and Shear

“Convergence” and “shear” determine the magnification and shape (ellipticity) of the image.

Distortion matrix

with the co-moving coordinate along the geodesic, and a function of angular diameter distances.

( )

Simulation courtesy of S. Colombi (IAP, France).

Weak Lensing of Distant Galaxies

Sensitive to cosmological distances, large-scale structure of matter, and the nature of gravitation.

Source galaxies are also lenses for other galaxies.

Observables and Survey Strategy

Galaxies are not round!

g ~ 30%

The cosmic signal is 1%.

Must average a large number of source galaxies.

Signal is the gradient of , with zero curl.

“B-Mode” must be zero.

Ellipticity (Shear) Measurements

16 arc-sec

2000 Galaxies 200 Stars

WHT Bacon, Refregier, and Ellis (2000)

i i/2

Instrumental PSF and Tracking

Mean ellipticity ~ 0.3%.

Images of stars are used to determine smoothed corrections.

Bacon, Refregier, and Ellis (2000)

Weak Lensing Results

Discovery (2000 – 2003) 1 sq deg/survey 30,000 galaxies/survey

CFHT Legacy Survey (2006) 20 sq deg (“Wide”) 1,600,000 galaxies

“B-Mode”

Requires Dark Energy (w0 < -0.4 at 99.7% C.L.)

Shear-Shear Correlations andTomography

Maximize fraction of the sky covered, and reach

zs ~ 3 to optimize

sensitivity to dark energy.

Two-point covariance computed as ensemble average over large fraction of the sky

ξ2() = < e(r) e(r+)>.

Fourier transform to get

power spectrum C(l).

Tomography

– spectra at differing zs.

zs = 1

CDM with only linear structure growth.

0.22 1’

Experimental and Computational Cosmology at KIPAC

Cosmic microwave background. (Church)

First objects, formation of galaxies. (Abel, Wechsler)

Clusters of galaxies and intergalactic medium. (Allen)

Supernovae. (Romani)

Gravitational lensing. (Allen, Burchat, Burke, Kahn)

Cosmic Microwave Background

Temperature

Polarization

WMAP QUaD

High resolution observations of CMB with QUaD at the South Pole.

Also studies of the Sunyaev-Zeldovich effect in galaxy clusters in combination with X-ray cluster investigations.

Supernovae with SDSS II

Fall 2005

160 1a SNe

SDSS 2.5m

Hobby-Eberly9.2m

Taking data through 2007.

Complete the magnitude-redshift distribution.

Formation of Galaxies and Clusters

Observations, theory, and simulations. New techniques and exploiting best available data.

Complementary constraints from different methods: eg direct distance measures, growth of structure and geometric.

Allen et al. Rapetti et al.

Gravitational Lensing by Clusters

Measurements of baryonic and dark matter in galaxy clusters from multi-wavelength observations (X-ray and gravitational lensing).

Gravitational potentials of baryonic and dark matter in clusters.

Separation of baryonic and dark matter in merging systems.

Allen et al. Bradac et al.

Large Synoptic Survey Telescope(Burchat, Burke, Kahn, Schindler)

8.4m Primary-TertiaryMonolithic Mirror

3.5° Photometric Camera

3.4m Secondary Mirror

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 4 nights for up to 10 years.

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

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 < 0.8).

Cosmology with LSST

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. 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.

Simultaneously in one data set.

LSST Site

Cerro Pachón

Gemini Southand SOAR

LSST Site

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%

Paul-Baker Three-Mirror Optics

8.4 meter primary aperture.

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

Camera and Focal Plane Array

Filters and Shutter

Focal Plane Array3.2 Giga pixels

~ 2mWavefront Sensors and

Fast Guide Sensors

“Raft” of nine 4kx4k CCDs.

0.65m Diameter

Aperture and Field of View

Primary mirror diameter

Field of view

KeckTelescope

0.2 degrees10 m

3.5 degrees

LSST

Optical Throughput – Eténdue AΩ

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

All facilities assumed operating100% in one survey

LSST Postage Stamp(10-4 of Full LSST FOV)

Exposure of 20 minutes on 8 m Subaru telescope. Point spread width 0.52 arc-sec (FWHM). Depth r < 26 AB.

Field contains about 10 stars and 100 galaxies useful for analysis.

1 arc-minute

LSST will see each point on the sky in each optical filter this well every 6-12 months.

Optical Filter Bands

Transmission – atmosphere, telescope, and detector QE.

Photometric Measurement of Redshifts – “Photo-z’s”

Galaxy Spectral Energy Density (SED)

Moves right larger z.Moves left smaller z.

“Balmer Break”

Photo-z Calibration

Calibrate with 20,000 spectroscopic redshifts.

Need to calibrate bias and width to 10% accuracy to reach desired precision

Simulation of 6-band photo-z.

z 0.05 (1+z)

Simulation photo-z calibration.

z 0.03 (1+z)

Shear Power Spectra Tomography

Linear regime Non-linear regime

CDM

1

0.22

Precision on Dark Energy Parameters

Measurements have different systematic limits.

Combination is significantly better than any individual measurement.

DETF Goal

Weighing Neutrinos

Free streaming of massive neutrinos suppresses large scale structure within the horizon distance at the time the neutrinos freeze out.

The suppression depends on the sum of the neutrino masses,

m

Hu, Eisenstein, and Tegmark 1998

m = 0.2

h = 0.65

P

Present Status and Forecast

Present atmospheric value:

m322 = 1.9 – 3.0 10-3 eV2 (90%CL),

or Σm > 0.044 eV.

Forecast for LSST (contours):

Σm 0.020 eV (statistical).

Hannastad, Tu, and Wong (2006)

Goobar, Hannestad, Mörtsell, Tu (2006)

CDM

Present Limits

14 3 2

Project Milestones and Schedule

2006 Site SelectionConstruction Proposals (NSF and DOE).

2007-2009 Complete Engineering and DesignLong-Lead Procurements

2010-2012 Construction

2013 First Light and Commissioning