modeling galaxy redshift space distortions for wfirst · • python tools for n-body simula’ons +...
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ModelinggalaxyredshiftspacedistortionsforWFIRST
NickHandUCBerkeleyMarch3,2016
withUrosSeljak,YuFeng,andGrigorAslanyan
GalaxyclusteringwithWFIRST
theul'mategoal:measureexpansionhistoryandgrowthratewithsub-percentlevelprecision
Andersonetal.2014 PlanckCollabora'onXIII2015
BAOasstandardruler redshiHspacedistor'ons
UncertaintiesintheforecastingofRSDconstraints
•smallscalescontaminatedbynon-lineareffects,buthavegreatersta's'calprecision
•theore'calsystema'csimplicitlyforecastedthroughvalueofkmax
source:Weinbergetal.2013
RSDconstraintshavegreatpotential
source:Wangetal.2010
•needfullP(k)analysistofullycaptureinforma'on
•factorof~3improvementindarkenergyFOMwhenusingfullP(k)shapemeasurements(assumingGR)
•fullshapeanalysisprovidesinforma'ononneutrinomassesandexpansionthroughAPtest
NickHand,UCBerkeley March3,2016
AnewschemeformodelingRSD
1.ApproximateN-bodysolverwithhaloforma'onmodelthatisbothsufficientlyfastandaccurateenoughtoextractgalaxysta's'cs
2.Physicalmodelforgalaxy-haloconnec'onthatisgeneralenoughtoavoidthemanyunknownaspectsofgalaxyforma'on
3.Simultaneouslysampletheposteriordistribu'onandemulatetheslowevalua'onofthedatalikelihood
NickHand,UCBerkeley March3,2016
FastPM:fastsimulationsofhalos
•anapproximatepar'clemeshN-bodysolverthatenforcesthecorrectlarge-scalelineargrowthateach'mestep
•wriXenfromscratchtoexhibitstrong-scaling—nearlylinearscalingwiththenumberofCPUsallowsforfastsimula'ons
•benchmarkswith10'mestepsproducehalocatalogsthatareveryclosetotheexact(N-body)solu'on
•simula'onsledbyYuFengatUCBerkeley,withpublica'oncomingsoon
findtheprojectongithub:hXps://github.com/rainwoodman/fastpm
NickHand,UCBerkeley March3,2016
preferredconfigura'ontakes~100CPU-hours—>typicallyO(1min)
Fengetal.2016(inprep.)
FastPM:fastsimulationsofhalos
NickHand,UCBerkeley March3,2016
FastPM:benchmarksforhalocatalogs
transfer(P
1/P 2)1/2
Fengetal.2016(inprep.)
atz=0
thegalaxy-haloconnection:HODformalism
•flexibleenoughtoimmunizeconstraintsagainstgalaxyforma'onuncertain'es:
1. velocitybiasforcentrals/satellites2. centralgalaxyincompleteness3. satelliteprofileuncertain'es4. assemblybias—>decoratedHODs(seeHearinetal.2015,
1512.03050)5. others?
•simplifiedHOD-modelingalreadysuccessfulinextendingRSDconstraintstosmallerscales:Reidetal.2014,Guoetal.2014.
•populateFastPMhalocatalogsusingasmanyfeaturesasneededusingHalotools soHware(ledbyAndrewHearin)
Halotools:hXps://github.com/astropy/halotools
0.2 0.4 0.6 0.8 1.0k (h/Mpc)
−0.5
0.0
0.5
1.0
1.5
2.0
Pgg ℓ)(,2/PEH
ℓ)((k)
satellitefrac'on
fromsimulationtoclusteringobservables
•fastpowerspectrummeasurementsviaFFTsvianbodykit• popula'on+powerspectrumstepstakeO(seconds)
nbodykit:hXps://github.com/bccp/nbodykit
monopole
quadrupole
todo:tailortoWFIRSTvolume,HODmasses,observa'onaleffects,etc
NickHand,UCBerkeley March3,2016
CombiningthepieceswithCosmo++ emulator
•acombinedsamplerandemulatorfordatalikelihoodusingtrainingsetofexactresultsproducedduringsamplingprocedure
•robusterrorcontrolofemula'onerrorsthatarepropagatedtoposteriorprobabilitydistribu'on
•exactsolu'oncomputediferrormodelpredictsanunacceptableemula'onerror
•“learn-as-you-go”:updateserrormodelandtrainingsetgivennew,exactsolu'ons
Aslanyanetal.2015,1506.01079hXps://github.com/aslanyan/cosmopp
NickHand,UCBerkeley March3,2016
ledbyGrigorAslanyanatUCBerkeley
appliedtoCMBlikelihoodsin1506.01079
Aslanyanetal.2015
CombiningthepieceswithCosmo++ emulator
Conclusions
• RSDanalysescanprovidepowerfulconstraintsondarkenergyandGeneralRela'vitytestswithWFIRST,iftheore'caluncertain'escanbecontrolled
• keychallenge:accuratemodelingofnon-lineareffectsandgalaxyforma'onphysicsonsmall-scales
• developingasimula'on-basedRSDmodelthatisbothcomputa'onallytractableandsufficientlyaccurate
1. FastPMsimula'onsproducehalocatalogsinO(minutes)2. HODpopula'onandpowerspectrumes'ma'onin
O(seconds)3. Combinethesestepsinlearn-as-you-goemulatorto
simultaneouslysampletheposteriorandemulatethenon-lineargalaxypowerspectrum
NickHand,UCBerkeley March3,2016
FastPM:benchmarksforhalocatalogsstochas'city
Fengetal.2016(inprep.)
~0.18dexscaXerinhalomasscorrespondsto:stochas'city~0.10,0.18,0.22in1012,1013,1014Msun/hhalos
NickHand,UCBerkeley March3,2016
ModelingassemblybiaswithdecoratedHODs
NickHand,UCBerkeley March3,2016
thecurrentstatusofgrowthrateresults
bestuncertaintyonfσ8(z=0.57)is~8%,fipngtokmax=0.24h/Mpc
Gil-Marinetal.2015
NickHand,UCBerkeley March3,2016
BAOsystematicsarewell-controlled
simula'onsindicatereconstruc'oneliminatessystema'cstothe~0.1%level
BAOsh
i1
source:Mehtaetal.2011
NickHand,UCBerkeley March3,2016
nbodykitsoftwaretools
•pythontoolsforN-bodysimula'ons+LSSsurveys
•parallelizedwithMPIanddesignedtorunonsuper-computers
•availabletools/features:
•periodicandwindowedpowerspectra
•correla'onfunc'ons
•FOFhalofinder
•sub-halofinder
•runningabovealgorithmsinparallelacrossnodesinbatchmode
availableatgithub.com/bccp/nbodykit