D. Schlegel, DESI@FNAL 27 May 2015 1
SpectroscopicSurveysBeyondDESIDavidSchlegel,BerkeleyLab
Outline
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- Redshi=surveyobjec?ves:mappinglinearmodes- DESIgoals+technologies- BeyondDESI
- DESI-II:200Mgalaxiesatz<2- FOBOS:Lyman-alphaatz>2
- Investmentstokeepus“onthecurve”
Redshift survey objectives: Map all the linear modes
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Cosmologicalinforma?oncontentisinthelinearregime
non-linear modes
linear perturbations on scales > 10 Mpc at z=0
Redshift survey objectives: Map all the linear modes
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Font-Ribera, McDonald, Slosar in prep.
Cosmologicalinforma?on(darkenergy,primordialPk,neutrinos)containedintheperturba?vemodesofthemaps
How many modes are there?
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CMB ~few million
modes
z=1066
~2billionlinearmodesfrom0<z<4(over20,000sqdeg)1.9millionmodestobemeasuredbyDESI2.1millionmodestobemeasuredbyLSST
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z=1066
CMB ~few million
modes
~2billionlinearmodesfrom0<z<4(over20,000sqdeg)1.9millionmodestobemeasuredbyDESI2.1millionmodestobemeasuredbyLSST
How many modes are there?
samefigure,logscale
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How many galaxies to measure these modes?
10milliongalaxies0<z<0.4120milliongalaxies0<z<1.52billiongalaxies0<z<4
Redshift surveys necessary to map all modes
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Redshi=surveysΔcz~300km/satz=0,preservesinforma?ondowntonon-linearregime(e.g.,smallscales)
Redshift surveys necessary to map all modes
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PhotometricsurveysΔcz~10,000km/satz=0,washesoutmanyofthelinearmodes;notrecoverableevenw/numbers
Low-resolution / photo-z redshifts pay a penalty
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Spa?alresolu?onhelpsto1”SpectralR>3000greatlyreducesskylevelbyremovingskylines
(relevantforground-basedinstruments)SpectralR>3000improvesredshi=s/n
Redshift surveys are necessary to map all modes
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Therearemoreobjectsofinterestonaspectroscopicfocalplanethanonanimagingfocalplane~10,000/deg2forimaging→informa?onhassaturated~100,000/deg2forspectroscopy
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HST Ultra-Deep Field 10,000 galaxies / (11 arcmin2)
Redshift surveys increasing 10X every 10 years
140 billion
1980 20611000
Year
log N(galaxies)SDSS, 2009 929,000
CfA1, 1983 1840
2dF, 2003 221,414
CfA-2, 1998 18,000
LCRS, 1996 18,678
SDSS-III, 2014 2.8 million
DESI 30 million
All linear modes mapped by ~2043 All detectable galaxies mapped by ~2061
4meterprimary1meterdiamcorrector5000fiber-robotarmy200,000metersfiberoptics10spectrographsx3cameras
DESI Goals + Technologies
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DESI Goals
DESI
4 million LRGs
17 million ELGs
0.7 million Ly-A QSOs +1.7 million QSOs
10 million BGS galaxies
35milliongalaxy+QSOredshi=survey
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How many galaxies to measure these modes?
10milliongalaxies0<z<0.4120milliongalaxies0<z<1.52billiongalaxies0<z<4
—>DESIwillmap~100%ofthese—>DESIwillmap~10%ofthese
integral
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DESI Technologies
6-lensop?calcorrector,1-mdiameter,includesADC
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DESI Technologies
Focalplatemoun?ng5000fiberrobots
TherobotarmyofDESIreplaceshand-pluggingoffibers
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DESI Technologies
10spectrographsX3cameras/spectrograph
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DESI Technologies
Forward-modelingofspectrodataofferssubstan?alimprovementsovertheold-school,20th-century,datareduc?onofSDSS-I
SDSS-IoperatedatS/N~hugeSDSS-III/BOSSoperatedatS/N~50DESIwilloperateatS/N~10
“data”
log 1
0 [ p
ixva
l / <
pixv
al>]
Model fiber PSF for
SDSS1 @ 8500Å
The future of redshift surveys?
Modest improvements in capability from SDSS-I → SDSS-III/BOSS → DESI
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Howhascapabilityimproved?• CCDs→improved,esp.inthered/infrared• CCDelectronics→lowernoise• Stabilityofcalibra?onsystems
•allowingbeoersky-subtrac?on,fainterobjects
Biggergainshavebeeninmul?plexing• Op?caldesignsforwiderfieldsontelescope&inspectrographs• Morefibers,hand-plugged→massively-parallelrobots
Technical challenges are cost effectiveness
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Pre-SDSS→SDSSrevolu?onMul?plexingfrom1-30objects→640objects
usingfiber-fedspectrographsIn2015,SDSShascollectedmoregalaxyredshi=s(2.7M)
thanallothertelescopesonearthcombined
Cost models for multi-objects spectrographs scaling from DESI
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Telescope+corrector($40M+$10M)*(Mirrorarea/4-m)2
Focalplane+spectrographs$1000XNfiber+$1MX(Nfiber/500)
Opera?ons$6M/yearX5years
+$200k+$50k
+$150k
+$300k
Costfor1%improvement
DESIcostmodelisreasonablywell-balancedMostimprovementwouldcomefrommorefibers,
butnotpossibleonDESIgivenotherdesignconstraints
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140 billion
1980 20611000
Year
log N(galaxies)SDSS, 2009 929,000
CfA1, 1983 1840
2dF, 2003 221,414
CfA-2, 1998 18,000
LCRS, 1996 18,678
SDSS-III, 2014 2.8 million
DESI 30 million
Future investments to keep us “on the curve”?
Future investments to keep us “on the curve”?
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Fiberrobotcosts→Pick-and-playfiberposi?oners(2dF,MMT,…)donotscale→Fiberrobotsw/1robotperfiberscales
~$10,000/fiberforSubaru/FMOSin~2006~$2000/fiberforSubaru/PFSin~2013~$700/fiberforDESIin~2015
Futureinvestments?→DOEstartedR&Din2006withLBNLLDRDsupport,followedbyDESIdevelopment→Con?nuedR&Dwouldfurtherreduceper-robotcosts
Two possible near-term redshift survey concepts
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Op?on1:DESI@KioPeak,LSST@CerroPachon10,000sqdegfootprintequatorial
Op?on2:DESI@CerroTololo14,000sqdegfootprintequatorial+south
DESI-II + LSST for z<2
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DESI-II + LSST for z<2
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1. Retain DESI @ Kitt Peak with 10,000 sq deg overlap, or move DESI instrument from Kitt Peak -> CTIO • Optics study from Tim Miller (16 Sep 2014) shows no
changes needed to the optics (in fact, it’s better there!) 2. Re-furbish instrument with faster electronics
• Probably necessary for shorter exposures 3. Target ~200,000,000 galaxies with the best photo-z’s
• LSST will have a parent sample of ~10 billion galaxies 4. Turn photo-z’s ➔ spectroscopic redshifts
• Δz~0.03 ➔ Δz~0.001
DESI-II + LSST for z<2
z
χr2
trialzz2nd best
χr2
∆too∆ z
small
parabola fit toestimate error δz
best
The trick: DESI operates at S/N > 7 DESI-II at S/N > 3
Bolton, Schlegel et al. 2012
FOBOS @Keck for z>2
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FOBOS @Keck for z>2
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1. Utilize Cass or Nasmyth focus at either Keck telescope 2. 1000-fiber robotic focal plane, using DESI technology 3. DESI spectrographs 4. High-density Lyman-alpha forest mapping at z > 2
Map from CALMAT program K.G. Lee
Longer-term redshift survey concept
What’s possible with current tech?
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1. Optical design from LAMOST/Guoshoujing telescope • ~2X aperture of DESI
2. DESI fiber positioners • 5X fiber positioners (25,000)
3. Survey speed increase 10X for galaxies at z < 2, 5X for Lyman-alpha forest at z > 2
Summary
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Linearmodesforcosmology—DESIwillmap~100%ofmodesatz<0.4
~10%ofmodesatz<1.5~2%ofmodesatz<4
—DESI-II+LSSTcouldmap100%ofmodesatz<1.5—“BeyondDESI”needonlymap~2billiongalaxiesatz<4
Ifthephotonsarevaluable…Spectroscopyiscost-effec?veuseofthosephotons
ForthisCosmicVisionsProcess…DESI-II+LSSTredshi=ingshouldbedemonstrated/simulated