the supernova / acceleration probe (snap)

SNAP OCU Project SLAC EPAC Meeting Nov. 14-15, 2003 1

The Supernova / Acceleration Probe

(SNAP)

Presentation to the Experimental Program Advisory Committee at SLAC.

November 14, 2003


SLAC Involvement in SNAP

• With the creation of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), experiments addressing issues at the interface between particle physics and astrophysics will play an increasingly prominent role in the SLAC research program.

• Of particular interest will be the “dark sector”, the nature of dark energy and dark matter, and the roles they play in the evolution of the Universe.

• Technology development in connection with the SNAP mission has been a cornerstone of the DOE-OS program addressing the mystery of dark energy.

• We believe that SLAC can and should play a prominent and important role in this mission if it goes forward as currently planned.


SLAC Involvement in SNAP

• The first discussions about SLAC involvement with the leadership of the SNAP collaboration (S. Perlmutter, M. Levi) were held in February 2003.

• At that time, a potential hardware role in the mission associated with the design and development of the Observatory Control Unit (OCU) was identified.

• We also highlighted our science interest in the use of SNAP data for strong lensing investigations.

• A letter of application for institutional membership in the SNAP collaboration on behalf of Stanford and SLAC was submitted in August 2003. That application is currently still under discussion, but the preliminary responses have been very positive.


Outline of Presentations

• The Science of Dark Energy and the Design of the SNAP Mission – E. Linder

• Strong Lensing Investigations with SNAP – R. Blandford

• The Observatory Control Unit – M. Huffer

• Concluding Comments – S. Kahn


National priorities

HEPAP: Scientic potential and facility need – absolutely central

Secretary of Energy (11/10/03) – SNAP has very high priority (#3 on list)


SLAC and SNAP

SLAC/Stanford major strengths include:

• Strong Gravitational Lensing – Blandford

Dark matter / dark energy / cosmology


SLAC and SNAP

Observatory control unit expertise – Huffer

Technical experience and development resources

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SLAC and SNAP

SLAC/Stanford major strengths include:

• Space mission experience – Kahn

Extensive design and implementation

Knowledge of NASA culture

• Experience with joint NASA-DOE projects from GLAST

Collaborative agency working relationships

• Dark Energy and High Energy Physics – Existing and ongoing SNAP theory collaboration by Kallosh & Linde


Revolutions in Physics

Lord Kelvin (1900): Two clouds on the horizon

The horizon is 95% cloudy!


Mapping our history

The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history.


Accelerating universe


What is dark energy?

• 70-75% of the energy density of the universe

• Accelerating the expansion, like inflation

• Determining the fate of the universe

But what is it? Einstein’s cosmological constant ? Problems: fine tuning and coincidence

Matter

Dark energy

Today Size=2 Size=4Size=1/2Size=1/4


Dark energy – discovery!

accelerating

decelerating > 0 at 99% confidence


Next generation

Supernova/Acceleration Probe: SNAP

Dedicated dark energy probe


Mission design

• ~2 m aperture telescope

Reach very distant SNe.

• 1 degree mosaic camera, ½ billion pixels

Efficiently study large numbers of SNe.

• 0.35 – 1.7 m spectrograph

Analyze in detail each SN.

Dedicated instrument designed

to repeatedly observe an area of

sky.

Essentially no moving parts.

3+ year operation for experiment

(lifetime open ended).


Mission design

Spectrograph

GuiderCCD’s

HgCdTe

BITE

Photometry: half-billion pixel mosaic camera, high-resistivity, rad-tolerant p-type CCDs (0.35-1.0 m) and, HgCdTe arrays (0.9-1.7 m).

Field of View Optical ( 36 CCD’s) = 0.34 sq. deg.

Four filters on each 10.5 m pixel CCD detector

Field of View IR (36 HgCdTe’s) = 0.34 sq. deg.

One filter on each 18 m pixel HgCdTe detector


Mission design

Field beforeslicing

Pseudo-slit

Slicing mirror (S1)

Spectrogram

Pupil mirrors(S2)

To spectrograph

Field optics (slit mirrors S3)

From telescopeand fore-optics

Input port

Slicer

PrismBK7 Prism

CaF2

NIRdetector

VisDetector

Integral field optical and IR spectroscopy:

0.35-1.7 m,

3”x6” FOV,

low resolution,

high throughput.


Mission design

15 sq.deg. Deep Survey ~300 sq.deg. Wide Survey

• 9 filters

• mAB=27.7 every 4 days

• 120 epochs • coadd AB=30.3 (31)

GOODS

HDF

• 9 filters

• mAB=28.1


SN control of systematics

Images

Spectra

Redshift & SN Properties

Lightcurve & Peak Brightness

data analysis physics

M and

Dark Energy Properties

Each supernova sends a rich stream of information about its physical state.


High energy physics


Complementarity

Next generation data will map the acceleration of the universe so precisely that it can probe:

• The nature of dark energy w(z)

• Structure of the vacuum

• w´(z) V´ / V()

• High energy physics


Fate of the universe

a

t

wa=2w´

w0

tdoom= ()

tdoom > 29 Gyr [95% SNAP]

tdoom > 35 Gyr [95%SNAP+CMB]

tdoom > 40 Gyr [95% SN+CMB+WL]

Kallosh, Kratochvil, Linde, Linder, & Shmakova JCAP 2003; astro-ph/0307185

First and simplest DE model: linear potential (Linde 1986) leads to collapsing universe.

Such models look like in the past, but develop a strong w´.


SNAP Cosmology and Physics

SN IaWeak Lensing

SN IIStrong LensingWide, Deep and Colorful

• 9000 times the area of Hubble Deep Field

• 10 billion years of detailed history

• 108 galaxies, 105 lenses, 9 wavelength bands


Strong Lensing Program

• Multiple imaging by galaxies, groups and clusters

• Ancillary program - complementary to:– Supernova cosmography– Weak lensing study of large scale structure– Galaxy-galaxy lensing study of galaxy halos

• Telescope nearly ideal for strong lensing because of– 9 filters– 0.1(0.05)” pixels– 4 day cadence– Deep (15 sq deg) and Wide (300 sq deg) surveys

• Lensing rate 0.001-0.002 => ~300,000 “events”– Quantitative, identification pipeline (cf CLASS)– Emphasize standard elliptical galaxy “scattering” with 0.5<z<1

• Complementary to LSST and Square Kilometer Array


Scientific Goals

• Source Population

– Study the faintest galaxies – building blocks of normal galaxies• redshift distribution

• luminosities

• star formation rates etc

– AGN microlensing– Rare high magnification events

• Lens Population– Galaxy substructure out to R ~ 10kpc– Cluster substructure

• Cosmography

• Propagation Effects– Time delays Þ small scale dark matter distribution– Quasar absorption lines etc


Source Population

• Understand empirically where when and how small galaxies merge to form larger galaxies

– ~2 x 105 isolated elliptical galaxy lenses on deep field– total cross section ~ 0.02 sq deg

– 10000 (30000) clean lenses on deep field to IAB

~ 28 (30)

– Use lens colors to measure lens distance– Use color maps to separate source from lens, remove dust– Use Einstein ring radius to measure source distance

• 100 times too faint for spectroscopy

– Infer source properties statistically and test CDM theory


Simulation

• Massive elliptical lens, I=21.5, at zd=0.7

• Faint blue galaxy, B=29, at higher redshift• Fit 9 images with two “spectral” models to reconstruct lensed

source

• Infer zs from Einstein ring radius

• Input images (true color, different intensity scales!):


Simulation

Simulated SNAP images:

• 0.12” pixels, 0.14” FWHM PSF, no dither • Deep survey, 1.5 mag fainter than HDF• B, V and I-bands shown for illustration:

B (440nm) V (582nm) I (770nm)


Simulation

Optimal weighting of 9 filters' images allows lens and source components to be separated


Simulation

Measuring source redshift with:• Einstein ring radius to ±1/4 pixel• Lens photo-z to ±0.02• Lens velocity dispersion to ±10 km s-1

=> Find 1.2 < zs < 1.5 (1) (true value = 1.3)

Lensing provides vital additional information to photo-z at high redshift


Scientific Goals



• luminosities




• Cosmography

• Propagation Effects– Time delays => small scale dark matter distribution– Quasar absorption lines etc


Cluster Arc Images

Multi-colour, high resolution surveying and imaging:

RCS0224 (CFHT): Cl0024 (HST):


Scientific Goals



• luminosities




• Cosmography

• Propagation Effects– Time delays => small scale dark matter distribution– Quasar absorption lines etc


Time delays

• Lens time delays measure the Hubble constant, age of universe

– Accuracy limited by lens model• Currently lens determinations are competitive with traditional

astronomical methods• By the time SNAP is launched this will probably be settled• Small scale structure along the line of sight causes deviation

from apparent pure Hubble expansion• Can measure statistically and check CDM predictions


B1608+656 delays

Time delays of 1-2 months, measured to precision of 1-2 days...

H0 = 75±6 km s-1 Mpc


Research underway and planned

• Simulations using Hubble images and projected SNAP resolution (including dithering) and sky/detector noise (Marshall)

– Establish procedure for data analysis pipeline to find clean and dirty lenses

– Establish procedure for refining elliptical potentials– Use Hubble Ultradeep Field to describe source population– Estimate accuracy for determining source properties

• Work with weak lensing group to develop strategy to combine strong and weak lensing studies of galaxy structure (Koopmans)

• Study rare, higher order catastrophes as (Baltz):– highly magnifying telescopes– probes of granularity of dark matter– surveying instruments


What instrument deliverable does SLAC propose?

• The Observatory Control Unit (OCU)

• Both a hardware (electronics) and software system

• Supervises and manages (on-station) observatory operation


Electrical Block Diagram

FilterWheel

Mass store

Primary

OCURedundant

Mass store

Redundant

Ka xmtPrimary

Ka xmtRedundant

Power

CD&H

ACS

S-bandTransponde

rPrimary

S-bandTransponde

rRedundant

Focal

Plane

Assembly

OCUPrimary

Shutter

Focus

Thermal

Power

1553 BusAfter H. Heetderks

200 GBytes

Spectrograph


Functional requirements

• Executes instrument’s observation plan– Transfer pointing requests to ACS– Controls CCD array parameterization and readout

• Science data management– Manage mass store– Route real-time and stored data to downlink transmitters

• Mechanism management, control, and operation– Telescope cover, optical shutter, stepper coils, etc…

• Power distribution and management


Functional requirements…

• Thermal management– Manage heater elements

• Primary, Secondary mirrors, telescope structure, etc…

– Survival heaters– Monitor and trend temperatures

– Housekeeping» Monitor instrument environment» Packetize and route as telemetry

• Data (Event) readout and acquisition• Command processing and distribution

– Command database definition and maintenance– Decoding, distribution, and execution


What is the scope of the OCU within the observatory?

• OCU performs electronic supervision of entire instrument

• Encompasses design, specification and implementation of…– The bulk of instrument’s digital electronics – A modest amount of analog electronics– The entire Flight Software System

• Executes the science mission …

• Natural consequence is significant role in defining….– instrument architecture– translation of science objectives to operational program


How does it fit within SLAC’s current program?

• OCU development requires a unique blend of skills…– Data Acquisition– Detector Monitoring and Control

• SLAC has extensive experience in these areas…– Successful, lead role within 2 major HEP experiments:

• SLD• BaBar

• SLAC has space heritage…– Lead role in both Electronics and Flight Software for GLAST– Demonstrated collaboration with NASA based labs

• SLAC has long history of successful collaboration with LBL– We enjoy a physical proximity…

• Phases well with GLAST and BaBar program– BaBar no longer in development – GLAST moving out of design/development stage


Concluding Comments

• In October 2003, NASA and DOE announced the results of a year-long discussion regarding the possibility for cooperation in a space-based mission devoted to exploring the nature of dark energy.

• The plan involves the development of a Joint Dark Energy Mission (JDEM).

• NASA/DOE will issue a single AO soliciting a dark energy science investigation requiring a space-based observatory. The science investigation will be PI-led and will be selected via open competition.

• The present schedule shows selection of the science investigation one year after the onset of new funding, leading to launch of the mission eight years later.


Organization of JDEM


Concluding Comments

• The proposed plan is for the SLAC team to participate in an LBNL-led proposal for a JDEM science investigation based on the SNAP concept.

• SLAC and LBNL have a long history of close cooperation in high energy physics experiments.

• The differences in culture between the NASA and DOE communities will introduce some challenges in making the JDEM concept work.

• SLAC’s extensive experience working with both agencies in the GLAST program should prove to be a key asset to the SNAP collaboration.

the supernova / acceleration probe (snap)

Documents

slac involvement

kahnslac epac meeting

listslac epac meeting

slac research program

snap mission

relationships dark energy

nature of dark energy

mystery of dark energy