BigBOSSBigBOSS The Ground-Based Stage IV BAO The Ground-Based Stage IV BAO

ExperimentExperiment

Nick MostekLawrence Berkeley National Lab

Cosmology in Northern California Meeting

May 15,2009

Lawrence Berkeley National LaboratoryDavid Schlegel

Chris BebekHenry Heetderks

Shirley Ho Michael Lampton

Michael Levi Nick Mostek

Nikhil Padmanabhan Saul Perlmutter

Natalie Roe Michael Sholl George Smoot

Martin White

White Paper ContributorsWhite Paper Contributors

National Optical Astronomy ObservatoriesArjun Dey

Tony Abraham Buell Jannuzi

Dick Joyce Ming Liang Mike Merrill Knut Olsen Samir Salim

• BEPAC, Fall 2007• Commissioned town hall meetings to determine science communities interest for

the next Beyond Einstein mission• Concluded that a Dark Energy probe was the highest priority

• NASA started JDEM, put out and RFI for space mission concepts for a stage IV dark energy mission, Spring, 2008

• SNIa, Weak Lensing, Clustering and BAO were considered primary objectives• Competition between three missions: SNAP, ADEPT, and Destiny

• After RFI submission, NASA determined not to have a competition but to come to consensus through Science Coordination Group• Jan. 2009, did not quite go as planned….• JDEM design centered around BAO, but never really addressed whether

it must be done from a space platform• Cost, design complexity, and timeline ballooned

A brief history of (biding) timeA brief history of (biding) time

• Announcement of Opportunity, Design, Launch… ???

Baryon Acoustic OscillationsBaryon Acoustic Oscillations

Map of Universe at 400,000 years (CMB)

Acoustic scale can be used as a “standard ruler” in both the transverse and radial line-of-sight directions

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Sound waves in the early universe plasma were frozen into the initial matter density distribution at recombination

One wave

Many super-imposed waves

WMAP

• Measuring distances accurately with BAO scale length is largely limited by the survey volume and redshift accuracy • Robust against systematic errors, sub-percent accuracies possible

• BigBOSS intends to extend the survey design and capabilities of BOSS into a Stage IV dark energy experiment

Mapping the UniverseMapping the Universe

Our observable Universe

Surface of last scattering M.Tegmark

Volume mapped by SDSS

Volume to be mapped by SDSS-III(ca. 2015)

BigBOSS

M. Blanton for SDSS

BAO Scale

The dense BigBOSS redshift survey over a ~100 (Gpc/h)3 volume will be a rich dataset for important cosmological studies.

Other Cosmological TestsOther Cosmological Tests

N.Padmanabhan, M. White

• Constraints on the growth of structure through redshift space distortions - Nikhil Padmanabhan, Will Percival, Martin White

• Deviations from non-Gaussianity in the early universe - Shirley Ho, Anze Slozar

Just getting started!

0.2<z<1: Luminous Red Galaxies (extended from BOSS footprint)

Spectroscopic TargetsSpectroscopic Targets

2<z<3.5: Ly forest from QSOs (pioneered from BOSS)1<z<2: Emission line galaxies

BigBigBOSSBOSS

Padmanabhan, 2004

• Large slit/fiber spectroscopic surveys require efficient target selection• LRG and QSO selection uses 4000Å and Ly break and with griz colors (BOSS)• Emission Line galaxies with bright [OII] can be selected to z=2 with ugr, but requires

deeper u-band data than is currently available over a large area of sky• Targeting efficiencies are >70%, possibly better with optimization studies

Target SelectionTarget Selection

Adelberger (2004)

• Above graph shows the [OII] line flux limit for a sky source density of 2000 dn/(dz.deg2)

• Both Zhu and Ilbert are in reasonable agreement from 0.8<z<2, particularly considering that such luminosity functions can easily vary by a factor of 2 or more

• A conservative [OII] minimum detectable line flux (MDLF) of 2.5E-17 ergs/s/cm2 (F[OII]=1E-16 cgs at z=2, reduced by a factor of 2 for split [OII] and another factor of 2 for margin)

[OII] Line Flux Sensitivity[OII] Line Flux Sensitivity

Direct measurements extrapolated

[OII] Spectrum Simulation[OII] Spectrum Simulation

Sky Lines

[OII] 3726, 3729, z=1.4

• The majority of BigBOSS redshifts will come from measuring the [OII] forbidden transition (rest-frame 3727Å), much like DEEP2 and MUCH different from JDEM

• To test line identification, extraction, and measurement error, simulated BigBOSS spectra generated over 4096 pixels from 8000-11000Ang (small fraction shown above)

• Sky lines are well resolved and subtracted from object spectra assuming noise from 25 sky fiber spectra

• After sky subtraction, [OII] doublet with single line MLDF = 2.5E-17 cgs flux is clearly visible above the noise (extracted S/N~8)

ObservedSpectrum

Sky-Subtracted Spectrum

25 Combined Sky Fiber Spectrum

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=

• Baseline telescope structure is the 4m Mayall telescope at Kitt Peak

• Secondary Mirror replacement for F5 beam, good match to fibers

• Focal plane consists of 4000 individually-actuated fiber positioners (1.25cm diameter each)

• Fibers feed 8 bench spectrographs, ranging in resolution from 2300-6000

• Each spectrograph has 3 dichroic arms to cover 340-1130nm

Telescope and InstrumentationTelescope and Instrumentation

5 deg2 FoV!

• Spectrograph detectors:• 4kx4k e2V CCD (blue), • 4kx4k and 2kx2k LBNL deep-depletion CCD (red)• 2kx2k, 1.7 m cutoff HgCdTe in 4-side buttable packages

• Cold plate mounts of SiC• Cold front-end electronics• Much of the detector development already done from SNAP

Telescope and InstrumentationTelescope and Instrumentation

LBNL CCDHgCdTe detector

SiC Mount

The BigBOSS BAO survey would accomplish the same statistical measurement as JDEM

Projected AccuracyProjected Accuracy

N. Padmanabhan

5.0 deg2 5.0 deg2 5.0 deg2 Notional survey start is 2015!

• BigBOSS is a ground-based Stage IV BAO survey• Primary science is BAO with sub-percent accuracy on dA and H(z) • Other important cosmological tests (z-space distortions, non-Gaussianity) are

being studied• BigBOSS FoM is comparable to the JDEM BAO program

• BigBOSS will cover 24k deg2 from 0.2<z<3.5 by targeting LRGs, ELGs, and Ly forest from QSOs

• Lion-share of redshifts will come from ELG [OII] doublet measured between bright sky lines from 1<z<2

• New fiber positioners from LBNL will vastly improve the pointing accuracy, spatial sampling, and reconfigure speed on the BigBOSS focal plane

• Notional survey will be carried out on the KPNO Mayall 4m starting in 2015 (see white paper, arXiv:0904.0468, or visit http://bigboss.lbl.gov)

BigBOSS is just getting started and is open to collaborating institutions!Contact PI David Schlegel at LBNL for more information.

SummarySummary