Future Dark Energy Surveys

Future Dark Energy Surveys R. Wechsler Assistant Professor KIPAC SLAC Annual Program Review

Overview • Future Dark Energy Surveys • Dark Energy Survey • LSST • SNAP • Dark Energy Probes • Baryon Acoustic Oscillations • Galaxy Clusters • Weak Lensing • SN • Theoretical Challenges • Simulations of Structure formation • The Galaxy-Dark Matter Connection • Personnel • Wechsler group: postdoctoral fellows Busha, Gerke, student Hao-Yi Wu + Blandford group, Allen group, Abel group + many others SLAC Annual Program Review

The Standard Cosmological Model • Basic accounting of the Universe’s present contents is in place • We know what dark matter does on a wide range of scales, but very little about what it is. • We know what the baryons are, but understanding their behavior and evolution requires modeling complex interactions over a vast range of scales. • We know very little about dark energy, except how much there is. SLAC Annual Program Review

The Dark Energy Challenge • Universe is dominated by Dark Energy driving us into a period of accelerated expansion. • What is causing it? • Why is de ~ dm • Why is de < 10120planck? • Its effect can be characterized through equation of state • w = /P w(a) = w0 + wa(1+a) • Measuring this equation of state and its evolution can provide clues to its nature: cosmological constant? Vacuum energy? Modification of gravity? • Goal is to get precise (few percent) determination of w and its change with time. • Extremely puzzling physics question that can mostly be determined through astronomical surveys. SLAC Annual Program Review

Dark Energy Probes • Expansion Rate • Supernovae: Standard Candles • Baryon Acoustic Oscillations: Standard Ruler • The decoupling of photons and baryons in the early universe imprints a feature on the large-scale clustering of galaxies at a given scale. • Systematics can come from non-linear bias, photo-z errors. • Growth of Structure • Weak lensing • focus for the next generation will be on the shear power spectrum, as probed by the shapes of background galaxies. E.g., DES will measure the shapes of ~ 3e8 galaxies, to determine the angular power spectrum in 4 redshift slices. • Systematics can come from photo-z errors, PSF, calibration. • Galaxy Clusters • The number of galaxy clusters is determined both by the geometry (volume) and the growth of structure. Excellent probe of DE. • Primary systematic is calibration of the mass--observable relation. SLAC Annual Program Review

Upcoming Dark Energy Surveys • The Dark Energy Survey • 525 nights using a new camera on the Blanco 4m telescope • 5000 sq. degrees of g, r, i, Z, Y imaging to r ~24. • Cluster counts, weak lensing, Baryon Acoustic Oscillations, SN • Overlap with VISTA imaging (better photoz’s); SPT SZ clusters • ~300 million galaxies • Large Synoptic Survey Telescope • 10 year survey with new 8.4m telescope, 3.2Gpix camera • 20000 sq. degrees of g, r, i, z, Y imaging to r ~ 27.5. • image 1/4 of the sky every 3 nights. • 10 billion galaxies • SNAP • Approx: 1000 sq degrees to 28th mag, with 0.15” seeing SLAC Annual Program Review

Theoretical Challenges • Next generation DE probes will be systematics limited. • In order to meet the challenge of few % constraints on dark energy parameters, need precision calibration of structure formation, e.g. • Dark matter and galaxy clustering • Dark matter halo mass function • Profiles and formation histories of dark matter halos • Also need a precise calibration of how galaxies trace the dark matter distribution • Important for Weak Lensing, BAO, Clusters, Photo-z’s. • Requires a very large dynamic range for the simulations, detailed and well-calibrated models SLAC Annual Program Review

Dark Matter Simulations SLAC Annual Program Review simulation by A. Kravtsov

Mock Galaxy Catalogs • In addition to pure dark matter properties, need to understand how galaxy formation affects the dark matter distribution, and also how galaxies trace the dark matter distribution. • Want to be able to test all analysis methods on realistic mock galaxy distributions before data is available. • Want to be able to marginalize over uncertainties in GF. • Major computational challenge: need to resolve better than kpc over several Gpc. • Our group has developed many techniques for constraining the galaxy--dark matter connection SLAC Annual Program Review

Mock Galaxy Catalogs • Current work: • Have provided a 5000 sq. degree catalog to DES depth to DES science working groups • Active engagement with photo-z, clusters, LSS, lensing. • These simulations have also provided the backbone for image simulations for both DES and LSST. • Exploring uncertainties in the galaxy distribution; working on improvements that will be possible as deeper data becomes available Wechsler & Busha SLAC Annual Program Review

1.6 Zmax 0.8 14.5 13.5 14.5 13.5 logMth logMth Forecasting DE Constraints From Clusters • Dark Energy constraints from clusters depend on: maximum redshift that clusters can be identified, minimum cluster mass that can be reliably detected, amount of scatter in mass observable relation, priors on mass-observable relation & scatter. • Our work distinguished by close connection with the observers developing the tools to make the measurements. zmax Wu & Wechsler In preparation SLAC Annual Program Review

Summary • The nature of dark energy is one of the foremost physics questions • Progress on determining the nature of dark energy over the next decade will be led by large galaxy surveys: • Weak Lensing • Baryon Acoustic Oscillations • Galaxy Cluster Counts • The constraints from these surveys will be systematics limited • Require precision characterization of structure formation • Require precise determination of the galaxy--dark matter connection • Simulation and computation play an increasingly important role. • Surveys will probe several Gpc • Need to resolve better than kpc scales over this volume, for a wide range of cosmological models • Need to accurately simulate galaxy formation or marginalize over unknown baryonic physics SLAC Annual Program Review

Future Dark Energy Surveys