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Baryon Acoustic OscillationsProspects of Measuring Dark Energy

Equation of State with LAMOST

Xuelei Chen (陳學雷 )

National Astronomical Observatory of China

KIAS workshop 2008.10.28 Seoul

arxiv:0809.3002

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Xin Wang (NAOC)

XC

Fengquan Wu (NAOC)

Zheng Zheng (IAS, Princeton)

Pengjie Zhang (SHAO)

Yongheng Zhao (NAOC)

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photon and matter spectrum

M. White 2007

4Sound Horizon and Peaks in power spectrum

Blake & Glazebrook 2003

Peaks at

model spectrum

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Standard Ruler for Cosmology

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Combined constraintsPercival et al 2007

DV(z=0.35)/DV(0.2)=1.812 +- 0.06

7Large Aperture Multi-Optical fiber Spectroscopic Telescope (LAMOST)

Located at Xinglong Station(117o 34' E, 40o 23' N)

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LAMOST: LAMOST: A meridian reflecting Schmidt telescopeA meridian reflecting Schmidt telescope

Main features large aperture (4-meter) wide field of view (5-degree)

observation only during the meridian transit (1.5-3 hours) of an object

observable sky -10o< dec <+90o ~24000 sqr. deg. limiting magnitude (1.5hr) b=20.5

4000 fibers spectroscopy (3700A-9000A)spectral resolution R=1000/2000 total # of spectra (3yr) 107

Technical innovationsactive optics for segmented thin mirrorsparallel controllable fiber positioning

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F

oV (

deg)

Diameter (m)

Original Definition of Scientific Goals of LAMOST

Wide field & large sample spectroscopy107 galaxies

Large scale structure of Universe, Cosmology

Physics of galaxies

107 starsGalactic structure, Stellar physics

106 quasars…Multi-waveband astrophysics

Status and Plan:

• Sep 2008, all hardwares in place

• going through engineering tests

• two workgroups appointed by the Survey Selection Committee: extragalactic (Yipeng Jing), Milky Way (Licai Deng); working for overall survey plans

• Apr 2009, survey plans

• Dec 2008 to 2009/10, commission period

• 2010/11-2015, regular spectroscopic survey

• data release (2 years after taken)

Selecting Targets

• generic galaxy survey

• LRG survey

• quasars

SDSS region: about 8000 deg2

SDSS MAINLAMOST MAIN

SDSS photometric catalog as input

14Selecting the Targets: Luminous Red GalaxiesLuminous Red Galaxies (LRG):

bright elliptical galaxies strongly clusteredmany in clusters or groupseasy to determine photometric z

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Target Redshift Distribution

main1: r<18.8main2: r<19.8LAMOST LRG(MegaZ)

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To what precision can we measure?

Seo & Eisenstein 2003:

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Error Estimates

18Design the survey: integration time

point source (QSO)exponential (spiral galaxy)de Vaucouleurs (elliptical galaxy)

assume sky background 20.5in r and i.

19Design the Survey: target surface density

Fiber Surface Density: 200Optimal for fiber positioning: 400-600

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Survey ideas

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Estimate of the Bias of the sample

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Estimate BiasUsing the HOD model:

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LRG bias

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We assume the HOD parameters given in Brown et al., arxiv:0804.2293

B band vs. other band: we assume matching density

b(z=0.475)=1.77, b(z=0.625)=2.29

QSO bias

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Wyithe & Loeb (2003), Marulli et al (2006)

QSO is triggered by major merger

QSO Luminosity Function

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QSO bias

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QSO1: g<20.5, QSO2: g<21.0, QSO3: g<21.65

Comparison with direct observation

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Porciani et al (2004) use 14000 quasar from 2dF/6dFto measure QSO bias

The bias obtained this way is slightly (10%-20%) greater.

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Effective Volume

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Error on power spectrum

Error on distance scales

Caution: error depends on bin size.

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33Improvement on Dark Energy EoS

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35Effect of Spectral Resolution on Figure of Merit (inverse of error ellipse area)

SDSS: FoM~2

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Simulation

SDSS LAMOST

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Summary

• A main survey of 1-2 magnitude deeper than SDSS could improve BAO measurement FoM by a factor of about 3-5.

• LRG survey fiber time is much smaller than MAIN1 but could achieve similar effective volume

• QSO survey could achieve large effective volume at large scales, but declines rapidly at small scales

• For BAO measurement, R=1000 is sufficient and economical

• May improve current DE constraint, but still not enough to give accurate answer on varying EoS.

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Thanks