July 7, 2008SLAC Annual Program ReviewPage 1 Future Dark Energy Surveys R. Wechsler Assistant Professor KIPAC

July 7, 2008SLAC Annual Program ReviewPage 2 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

July 7, 2008SLAC Annual Program ReviewPage 3 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.

July 7, 2008SLAC Annual Program ReviewPage 4 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 <  planck ? *Its effect can be characterized through equation of state –w =  /P w(a) = w 0 + w a (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.

July 7, 2008SLAC Annual Program ReviewPage 5 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.

July 7, 2008SLAC Annual Program ReviewPage 6 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 ~ –image 1/4 of the sky every 3 nights. –10 billion galaxies *SNAP –Approx: 1000 sq degrees to 28th mag, with 0.15” seeing

July 7, 2008SLAC Annual Program ReviewPage 7 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

July 7, 2008SLAC Annual Program ReviewPage 8 simulation by A. Kravtsov Dark Matter Simulations

July 7, 2008SLAC Annual Program ReviewPage 9 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

July 7, 2008SLAC Annual Program ReviewPage 10 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

July 7, 2008SLAC Annual Program ReviewPage 11 logM th Z max logM th 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. Wu & Wechsler In preparation zmax

July 7, 2008SLAC Annual Program ReviewPage 12 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