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WFIRST Science with Clusters of GalaxiesMegan DonahueMichigan State University
AAS 2016
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WFIRST benefits cluster science
High resolution
Large field of view
Optical - infrared sensitivity to emission from stars
Low sky background
What can be gained by increasing reliably-characterized samples with precision mass
estimates from 10s to >1000s?
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Features of clustersClusters are the most massive gravitationally-bound systems (up to ~1015 solar masses)
Nearly representative census of matter (gas, stars, dark matter) within ~10 Mpc scales
Intergalactic and circumgalactic gas accessible in emission and in absorption.
Hosts the most massive galaxies and supermassive black holes.
Natural laboratories for high-density galaxy environments with large numbers of galaxies (100s-1000s)
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Massive Clusters are:85% dark matter
13% gas1-2% stars
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Dark Matter, SimulatedDiemer & Kravtsov 2014
62.5 Mpc/h 15 Mpc/h
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Dark Matter, SimulatedDiemer & Kravtsov 2014
62.5 Mpc/h 15 Mpc/h
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CLASH Ensemble Mass Profile
Umetsu+2015
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MACSJ1206.2-0847 z=0.44HST
Subaru
Umetsu+2012
Wide-field imaging allows HST-level PSF and galaxy densities over arcminute
scales
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MACSJ1206.2-0847 z=0.44HST
Subaru
Umetsu+2012
Wide-field imaging allows HST-level PSF and galaxy densities over arcminute
scales
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MACSJ1206.2-0847 z=0.44HST
Subaru
Umetsu+2012
Wide-field imaging allows HST-level PSF and galaxy densities over arcminute
scales
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MACSJ1206.2-0847 z=0.44HST
Subaru
Umetsu+2012
Wide-field imaging allows HST-level PSF and galaxy densities over arcminute
scales
WFIRST FOV
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Legacy of HST-CLASH and HST Frontier Fields
Software and modeling tools for analyzing weak and strong-lensing data (SaWLenS, Lenstool, WSLAP+, also codes from Zitrin+2015, Umetsu+2011)
Value of X-ray, SZE, and galaxy kinematics (velocity dispersion, caustics)
Shared data, tools, and derived products (magnification maps, selection volume estimates, etc.)
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Magnifying the high-redshift universeCoe+2012
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Magnifying the high-redshift universeCoe+2012
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Magnifying the high-redshift universe
Richard+2014
Coe+2012
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Magnifying the high-redshift universeCoe+2012
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Lensing with WFIRST
Cluster lensing causes shear, deflection, and magnification of background galaxies.
Combining weak-shear, magnification, and strong-lensing mitigates the mass-sheet degeneracy.
WFIRST will measure total gravitational masses, mass radial profiles, 2-d mass structures around clusters and galaxies with resolution unfeasible from the ground.
M(R>Rvir) and large-scale filaments will be characterized.
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Galaxy density
Resolution in lensing is limited by numbers of galaxies for which a shear measurement can be made.
The High-Latitude Survey density: ~75 galaxies per square arcminute in co-added J & H bands
Targeted GO observations could achieve 200-300 galaxies per sq. arcmin.
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empirical scaling laws
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Example of Cluster M-TxLieu+2015
38 clusters from XMM LSS survey +
CFHTLens
Core included
mass-concentration assumed
self similarity predicts M ~ T3/2
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Example of Cluster M-TxLieu+2015
38 clusters from XMM LSS survey +
CFHTLens
Core included
mass-concentration assumed
self similarity predicts M ~ T3/2
+20 CLASH clusters
Lensing w/HST data gives smaller uncertainties.
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Scaling lawsare Nature’s way of trying to show us how it works.
Gravitational potential or M/R (v2) is a key property of matter halos
Gravitational lensing M/R estimates are independent of assumptions of equilibrium, systematics different from other mass estimators
Kirby+2013
Star mass-star metallicity
SMBH-galaxy velocity
dispersionMcConnell & Ma 2013
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Galaxy masses from lensing
LRG 3-757Discovery and characterization possible with WFIRST
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Strong Lensing mass measurements of individual galaxies
figure from CLASH data courtesy Marc Postman
but WFIRST choice of the bluest filter might matter
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The nature of collisionless (?) dark matter
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Strong Lensing: testing the nature of dark matter
RCS2 032727-132623Rigby+2012
Abell 3827Image credit ESO
Massey+2015
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Understanding galaxy evolution
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FeedbackLx ~ T3 indicates IC gas entropy is elevated (cold infall gives Lx ~T2) (Kaiser+1986, 1990) [T ~ M/R]
Feedback is required to explain this scaling relation.
XMM cluster survey, (Hilton+2012)
Blue: no BH feedbackRed: with BH feedback
(Puchwald+2008)
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FeedbackLx ~ T3 indicates IC gas entropy is elevated (cold infall predicts Lx ~T2) (Kaiser+1986, 1990) [T ~ M/R]
Cluster atmospheres show evidence of powerful AGN outbursts and AGN-driven metal enrichment.
McNamara+2009; figure f/Sternbach+2009
Perseus; Fabian+2005 HCG62; UBirmingham MS0735; Kirkpatrick & McNamara 2015
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AGN and stellar feedback depend on system gravitational potential.
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Baryon census: Intracluster/intergalactic stars
Gonzalez+2007Fraction?
Evolution with redshift?
Metallicity high or low?
Difficult to measure: WFIRST low background, high resolution will make it easier.
Difficult to model
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Baryon census: Intracluster/intergalactic stars
Gonzalez+2007Fraction?
Evolution with redshift?
Metallicity high or low?
Difficult to measure: WFIRST low background, high resolution will make it easier.
Difficult to model
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Cluster CosmologyCluster number N(z,M) and spatial clustering are exquisitely sensitive to cosmological parameters such as Ωm, σ8.
Cluster N(z,M) tests alternative-GR explanations for dark energy, and can be cross-calibrated.
Selection by significance of lensing peak “clean”, and can be simulated.
Image credit: Meneghetti & Natarjan
HST synthetic image w/SL.
Recovery of cosmological constants,
simulated.
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Science considerations for cluster science with WFIRST
Choice of fields for the high-latitude survey: optimal overlap with other surveys: LSST, Euclid, eRosita, SZ, spectroscopy.
Observation strategies: dithers, depth
Optimal number and type of pointed observations towards the most massive (and therefore rare) systems.
Filter choices: blue range for increased strong lensing contrast; redder coverage for better sampling of the stellar peak.
Much work needed: simulators, lensing experts, and survey experience required.
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WFIRST cluster sciencesystematics-limited lensing masses for clusters and groups and a subset of galaxies
discovery and characterization of distant and massive clusters with a well-defined selection method
dark matter characterization: radial distributions, tests of collisionless nature
mass scaling laws (including trends and scatter) to test and inform our understanding of how galaxies and AGN evolve
Cluster galaxy evolution, galaxy stellar light, intracluster stars
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WFIRST will transform the nature of cluster science
Vastly increased samples of accurate mass measurements of individual systems: can quantify mean and mass trends and scatter and evolution.
Quantifiable selection bias independent of system state (such as equilibrium, virialization)
High quality, large-area measurements of mass fields
Low sky, low instrumental noise measurements of faint stellar light over large areas