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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