# Presentation: 686938

## LSST: Dark Matter and Dark Energy

**Tony Tyson**
***Director, LSST***
***Physics Dept.***
***UC Davis***

## deep  wide fast

***deep  wide fast***

## LSST Ranked High Priority By US Review Committees

- NRC Astronomy Decadal Survey (AANM)
- NRC New Frontiers in the Solar System
- NRC Quarks-to-Cosmos
- Quantum Universe
- Physics of the Universe
- SAGENAP
- NSF OIR 2005-2010 Long Range Plan
- Dark Energy Task Force
- P5 Report, HEPAP - October 2006

## Relative Etendue (= A)

- All facilities assumed operating100% in one survey

- All facilities assumed operating100% in one survey

##  Massively Parallel Astrophysics

-  Dark matter/dark energy via weak lensing
-  Dark matter/dark energy via baryon acoustic oscillations
-  Dark energy via supernovae
-  Dark energy via counts of clusters of galaxies
-  Galactic Structure encompassing local group
-  Dense astrometry over 20000 sq.deg:  rare moving objects
-  Gamma Ray Bursts and transients to high redshift
-  Gravitational micro-lensing
-  Strong galaxy & cluster lensing: physics of dark matter
-  Multi-image lensed SN time delays: separate test of cosmology
-  Variable stars/galaxies: black hole accretion
-  QSO time delays vs z: independent test of dark energy
-  Optical bursters to 25 mag: the unknown
-  5-band 27 mag photometric survey: unprecedented volume
-  Solar System Probes: Earth-crossing asteroids, Comets, trans- Neptunian objects

- Strong gravitational lensing with multiple images provides  a sensitive probe of dark matter mass distributions. LSST will find many of these.

- Image of a z=1.7 galaxy being multiply lensed by a z=0.4 mass cluster

*Physics of Dark Matter*

## Mass in CL0024

**Detailed map **
**of dark matter**

## Space vs Ground imaging of CL0024

- HST  0.1 arcsec

- 4m ground-based  1.2 arcsec

## Mass in CL0024

**LSST will measure total neutrino mass**

- LSST WL+BAO+P(k)  + Planck

## LSST and Dark Energy

- The only observational handle that we have for understanding the properties of dark energy is the expansion history of the universe itself.  This is parametrized by the Hubble parameter:
- Cosmic distances are proportional to integrals of *H(z)**-1* over redshift.  We can constrain *H(z)* by measuring luminosity distances of standard candles (Type 1a SNe), or angular diameter distances of standard rulers (baryon acoustic oscillations).
- Another powerful approach involves measuring the growth of structure as a function of redshift.  Stars, galaxies, clusters of galaxies grow by gravitational instability as the universe cools.  This provides a kind of cosmic “clock” - the redshift at which structures of a given mass start to form is very sensitive to the expansion history.

## LSST Probes Dark Energy in Multiple Ways

**Cosmic shear (growth of structure + cosmic geometry)**
**Counts of massive structures vs redshift (growth of structure)**
**Baryon acoustic oscillations (angular diameter distance) **
**Measurements of Type 1a SNe (luminosity distance)**
**Mass power spectrum on very large scales tests CDM paradigm**
**Shortest scales of dark matter clumping tests models of dark matter particle physics**

***The LSST survey will address all with a single dataset!***

## 

**D****LS**

**D****S**

-   = 4GM/bc2

- b

****

****

**D****LS**

**D****S**

- 4GM/bc2

- sheared image

- shear

- Gravity & Cosmology change the growth rate of mass structure

- Cosmology changes geometric distance factors

**“*****Weak Lensing*****”**

## Cosmic Shear

- The term “cosmic shear” refers to the systematic and correlated distortion of the appearance of background galaxies due to weak gravitational lensing by the clustering of dark matter in the intervening universe.
- As light from background galaxies passes through the intergalactic medium, it gets deflected by gravitational potentials associated with intervening structures.  A given galaxy image is both displaced and sheared.
- The effect is detectable only statistically.  The shearing of neighboring galaxies is correlated, because their light follows similar paths on the way to earth.

## LSST and Cosmic Shear

- The simplest measure of cosmic shear is the 2-pt correlation function measured with respect to angular scale.
- This is usually plotted as a power spectrum as a function of multipole moment (similar to the CMB temperature maps).
- Note the points of inflection in these curves.  This is a transition from the linear to the non-linear regime.
- The growth in the shear power spectrum with the redshift of the background galaxies is very sensitive to *H(z)*.  This provides the constraints on dark energy.

## Photometric Redshifts

- Galaxies have distinct spectra, with characteristic features at known rest wavelengths.
- Accurate redshifts can be obtained by taking spectra of each galaxy.  But this is impractical for the billions of galaxies we will use for LSST cosmic shear studies.
- Instead, we use the colors of the galaxies obtained from the images themselves.  This requires accurate calibration of both the photometry and of the intrinsic galaxy spectra as a function of redshift.

## Comparing HST with Subaru

## Comparing HST with Subaru

## LSST is Optimally Sized for Measurements of Cosmic Shear

- On small scales, the shear error is dominated by shape noise - it scales like the sqrt of the number of galaxies per sq. arcmin. Systematic error: baryons
- On larger scales, cosmic variance dominates - it scales like the sqrt of the total solid angle of sky covered.
- From the ground, the number of galaxies per squ. arcmin levels off at  mag 26.5.
- With the LSST etendue, this depth can be achieved over the entire visible sky.

## Cosmic Shear - Dealing with Systematics

- The cosmic shear signal on larger angular scales is at a very low level.
- To make this measurement, we must be confident that we understand and can remove spurious sources of shear.  These can arise in the atmosphere or in the optics of the telescope and camera.
- LSST is the first large telescope designed with weak lensing in mind.  Nevertheless, it is essentially impossible to build a telescope with no asymmetries in the point spread function (PSF) at the level we require.
- Fortunately, the sky has given us some natural calibrators to control for PSF systematics:  There are 3 stars per square arcmin bright enough to measure the PSF in the image itself.  Light from the stars passes through the same atmosphere and instrumentation, but is not subject to cosmic weak lensing distortions.  By interpolating the PSF’s, we deconvolve spurious shear from the true cosmic shear signal we are trying to measure.  The key issue is how reliable is this deconvolution at very low shear levels.

## Cosmic Shear Systematics:  E-B mode Decomposition

- E-mode (curl-free)

- B-mode (curl)

- The shear is a spin-2 field and consequently we can measure two independent ellipticity correlation functions. The lensing signal is caused by a gravitational potential and therefore should be curl-free. We can project the correlation functions into one that measures the divergence and one that  measures the curl: E-B mode decomposition.

- A residual B-mode is an indication of spurious shear in the analysis.

## Measuring Shear Residuals Directly

- A key aspect of the LSST design is that we have very short exposure times (15 s).  This enables us to obtain several hundred visits per field in each color over the life of the survey -  2,000 exposures for every sky patch.
- This allows us to optimize the shear extraction algorithms, leading to tremendous reduction in systematics.
- Experience in particle physics expts shows that the systematic errors fall faster than root N  - more like 1/N.

## Raw  

- PSF corrected

**Single exposure in 0.7 arcsec seeing**

**<shear> **
** ****= 0.07**

**<shear> **
** ****< 0.0001**

## Residual Subaru Shear Correlation

- Test of shear systematics:
- Use faint stars as proxies for galaxies, and calculate the shear-shear correlation.
- Compare with expected cosmic shear signal.
- Conclusion: 300 exposures per sky patch will yield negligible PSF induced shear systematics. Wittman (2005)

## Systematics in Photo-z’s

- Photometric redshift accuracy is limited by the statistical quality of the data and by the location of the key spectral features with respect to the passbands which are used.
- The dominant features are the Balmer and Lyman breaks at 400 nm and 91 nm, respectively.  As these move through the bands, the noise in the photo-z inversion rises and falls.
- There can also be catastrophic failures due to multiple minima associated with confusion between these two features.

## Systematics in Photo-z’s

- There are various statistical issues that can be investigated using Monte Carlo techniques to quantify the impact of photo-z errors on dark energy parameter estimations.  Priors on size and mag help reduce the catastrophic failures.
- But we are still left with the fundamental issue of calibration, since we don’t know the distribution of intrinsic galaxy spectra at higher redshifts.
- Brute force calibration would require an enormous number of spectroscopic measurements.  Fortunately, it appears that making use of the intrinsic clustering properties of galaxies can reduce this number to a manageable level.

## 12-band Super Photo-z Training Set

- Using angular correlations this training set enables LSST photo-z error calibration to better than required precision

- Systematic error:
- 0.003(1+z)  _*calibratable*_
- Need 20,000 spectroscopic redshifts overall.

## Another measure of distance

-   Measure redshifts & positions of billions of galaxies
-  Measure apparent angle of galaxy correlations
-  Use standard ruler to measure distance

**Example: standard ruler**

*d*

**s**

******s**

**standard ruler**

## Cosmic Fireball Standard Ruler

- + *R*S~1/3 billion  light-years

**distance vs   redshift **

- (Angular & radial scales)

- (Sound horizon at recombination)

- CMB

**“*****Baryon Acoustic Oscillations*****”**

## The DETF identified the “w”  as the key dark energy quantity to study.

- Dark energy pressure

- Dark energy density

- The DETF modeled “*w*” with two simple parameters:

- (“*  *” is a measure of cosmic time, *w=-1* is a “cosmological constant”)

## LSST Precision on Dark Energy 

- WL+BAO and Cluster counts give separate estimates.  Both require wide sky area deep survey.

- Zhan 2006

- p**/********= *****w******0 ******+ w******a *****(1-****a)***** ***

## LSST

*Wang et al. 2006, AAS*

**Precision vs Integrated Luminosity**

- Separate probes

- Combined probes

- Combining probes removes degeneracies

## LSST Project Organization

**LSST Project Organization**

- The LSST is a public/private project with public support through NSF-AST and DOE-OHEP.
- Private support is devoted primarily to project infrastructure and fabrication of the primary/tertiary and secondary mirrors, which are long-lead items.
- NSF support is proposed to fund the telescope.  DOE support is proposed to fund the camera.
- Both agencies would contribute to data management and operations.

- LSST Organization Chart

## There are 22 LSSTC Institutional Members

- Brookhaven National Laboratory
- California Institute of Technology
- Columbia University
- Google Corporation
- Harvard-Smithsonian Center for Astrophysics
- Johns Hopkins University
- Las Cumbres Observatory
- Lawrence Livermore National Laboratory
- National Optical Astronomy Observatory
- Princeton University

- Purdue University
- Research Corporation
- Stanford Linear Accelerator    Center
- Stanford University –KIPAC
- The Pennsylvania State University
- University of Arizona
- University of California, Davis
- University of California, Irvine
- University of Illinois at     Champaign-Urbana
- University of Pennsylvania
- University of Pittsburgh
- University of Washington

## The LSST optical design: three large mirrors

## The LSST will be on El Penon peak in

**The LSST will be on El Penon peak in**
**Northern Chile in an NSF compound**

**1.5m photometric**
**calibration telescope**

## The Telescope Mount and Dome

**Altitude over azimuth configuration**

**Camera and**
**Secondary assembly**

**Carrousel dome**

**Finite element**
**analysis**

## The LSST camera will have 3 Gigapixelsin a 64cm diameter image plane

**The LSST camera will have 3 Gigapixels****in a 64cm diameter image plane**

**Five Filters in stored location**

**L1 Lens**

**L2 Lens**

**Shutter**

**L1/L2 Housing**

**Camera Housing**

**L3 Lens**

**Raft Tower**

**Filter in light path**

**Notes:**
Contents:
	L1/L2 Housing
	Filter Changer and Carousel
	Shutter
	Assembly planning
	Packaging and internal interfaces
	Support structure and utilities
	External interfaces
	Access and servicing concepts

## The LSST Focal Plane

**Guide Sensors (8 locations)**

**Wavefront Sensors (4 locations)**

**3.5 degree Field of View (634 mm diameter)**

_**Curvature Sensor Side View Configuration**_

**The LSST Focal Plane**

***9.6 square degrees***

## Raft Towers

**Raft Towers**

**SENSOR**

**RAFT**

**RAFT TOWER**

**Si CCD Sensor**

**Raft Structure**

**Sensor Packages**

**CCD Carrier**

**Thermal Strap(s)**

**FEE Cage**

## LSST Data Management Model

** **

_**Applications**_** ******** Science**
**     **Image processing, database queries, ...

_**Middleware**_** ******** Interface wrapper**
**    **Device drivers, system management,...

_**Infrastructure**_** ******** Hardware**
**     **Computers, disks, data links, ,,,

_**LSST Data Management Model**_

- LSST generates 6GB of raw data every 15 seconds
- that must be calibrated, processed, cataloged,
- indexed, and queried, etc. often in real time** **

**The LSST Data Management Challenge:**

## Computing Requirements

## Timeline for the LSST

*Commissioning*

*Operations*

**Timeline for the LSST**

***FY-06       2007      2008       2009     2010       2011      2012     2013       2014      2015  ***

*Design and Development*

*Submit NSF MREFC Proposal*

*NSF and CD-3 funding begins *

*First light*

* **51 months*

*CD-0*

*(and early procurement)*

***Fiscal ***
***Years***

- 2006 base-year dollars
- Then-year dollars is ~$335M

## Comparison of Stage-IV facilities for DE

## w0-wa can only do these

- DE models can do this
-  (and much more)

- w

- z

**How good is the DETF w(a) ansatz?**

*z *= Another measure of cosmic time, z=0=today

## LSST and Fundamental Physics

**Unique experiment for Dark Energy physics:**
**Five separate types of probes from the same experiment**
**Precision control of systematics enabled by multiple chops**
**Ultra-deep 2******** sky coverage**
**Incisive probe of dark matter clumping on scales relevant to the underlying physics.**

## http://www.lsst.org

**http://www.lsst.org**

## LSST Optical Design

***f/1.23***** **
**< 0.20 arcsec FWHM images in six bands: 0.3 - 1 ********m**** **
**3.5 ****° FOV  ******** ****Etendue = 319 m****2****deg****2**** **

**LSST optical layout**

**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 )**

**Image diameter ( 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%

## Comparing Space with Ground: Weak Lensing

## LSST Science Collaborations 

- Supernovae: M. Wood-Vasey (CfA)
- Weak lensing: D. Wittman (UCD) and  B. Jain (Penn)
- Stellar Populations: Abi Saha (NOAO)
- Active Galactic Nuclei: Niel Brandt (Penn State)
- Solar System: Steve Chesley (JPL)
- Galaxies: Harry Ferguson (STScI)
- Transients/variable stars: Shri Kulkarni (Caltech)
- Large-scale Structure/BAO: Andrew Hamilton (Colorado)
- Milky Way Structure: Connie Rockosi (UCSC)
-  Strong gravitational lensing: Phil Marshall (UCSB)

*171 signed on already, from member *
*institutions and project team.*