Munch September 5, 2006
	Note:  Special day and time, Tuesday, 12:00 - 1:00 !!!!!
FAQ What is Munch? Munch Archive --------- 26June 2006 19 June 2006 12 June 2006 5 June 2006 22 May 2006 15 May 2006 8 May 2006 1 May 2006 24 Apr 2006 17 Apr 2006 10 Apr 2006 03 Apr 2006 27 Mar 2006 13 Mar 2006 6 Mar 2006	Can Cosmic Structure form without Dark Matter? Authors: Scott Dodelson, Michele Liguori Comments: 5 pages, 3 figures One of the prime pieces of evidence for dark matter is the observation of large overdense regions in the universe. Since we know from the cosmic microwave background that the regions that contained the most baryons when the universe was ~400,000 years old were overdense by only one part in ten thousand, perturbations had to have grown since then by a factor greater than $(1+z_*)\simeq 1180$ where $z_*$ is the epoch of recombination. This enhanced growth does not happen in general relativity, so dark matter is needed in the standard theory. We show here that enhanced growth can occur in alternatives to general relativity, in particular in Bekenstein's relativistic version of MOdified Newtonian Dynamics (MOND). The vector field introduced in that theory for a completely different reason plays a key role in generating the instability that produces large cosmic structures today. Full-text: PostScript, PDF, or Other formats Gravitational Lensing in Modified Gravity and the Lensing of Merging Clusters without Dark Matter Authors: J. W. Moffat Comments: 8 pages, one figure, LaTex file Gravitational lensing in a modified gravity (MOG) is derived and shown to describe lensing without postulating dark matter. The recent data for merging clusters identified with the interacting cluster 1E0657-56 is shown to be consistent with a weak lensing construction based on MOG without exotic dark matter. Full-text: PostScript, PDF, or Other formats The survival and disruption of CDM micro-haloes: implications for direct and indirect detection experiments Authors: Tobias Goerdt (1), Oleg Y. Gnedin (2), Ben Moore (1), Jürg Diemand (3), Joachim Stadel (1), ((1) University of Zürich, (2) Ohio State University, (3) UC Santa Cruz) Comments: 9 pages, 12 figures, submitted to MNRAS If the dark matter particle is a neutralino then the first structures to form are cuspy cold dark matter (CDM) haloes collapsing after redshifts z ~ 100 in the mass range 10^{-6} - 10^{-3} Msun. We carry out a detailed study of the survival of these micro-haloes in the Galaxy as they experience tidal encounters with stars, molecular clouds, and other dark matter substructures. We test the validity of analytic impulsive heating calculations using high resolution N-body simulations. A major limitation of analytic estimates is that mean energy inputs are compared to mean binding energies, instead of the actual mass lost from the system. This energy criterion leads to an overestimate of the stripped mass and underestimate of the disruption timescale since CDM haloes are strongly bound in their inner parts. We show that a significant fraction of material from CDM micro-haloes can be unbound by encounters with Galactic substructure and stars, however the cuspy central regions remain relatively intact. Furthermore, the micro-haloes near the solar radius are those which collapse significantly earlier than average and will suffer very little mass loss. Thus we expect a fraction of surviving bound micro-haloes, a smooth component with narrow features in phase space, which may be uncovered by direct detection experiments, as well as numerous surviving cuspy cores with proper motions of arc-minutes per year, which can be detected indirectly via their annihilation into gamma-rays. Full-text: PostScript, PDF, or Other formats Cosmological Constraints from the SDSS Luminous Red Galaxies Authors: M. Tegmark, D. Eisenstein, M. Strauss, D. Weinberg, M. Blanton, J. Frieman, M. Fukugita, J. Gunn, A. Hamilton, G. Knapp, R. Nichol, J. Ostriker, N. Padmanabhan, W. Percival, D. Schlegel, D. Schneider, R. Scoccimarro, U. Seljak, H. Seo, M. Swanson, A. Szalay, M. Vogeley, J. Yoo, I. Zehavi, K. Abazajian, S. Anderson, J. Annis, N. Bahcall, B. Bassett, A. Berlind, J. Brinkmann, T. Budavari, F. Castander, A. Connolly, I. Csabai, M. Doi, D. Finkbeiner, B. Gillespie, K. Glazebrook, G. Hennessy, D. Hogg, Z. Ivezic, B. Jain, D. Johnston, S. Kent, D. Lamb, B. Lee, H. Lin, J. Loveday, R. Lupton, J. Munn, K. Pan, C. Park, J. Peoples, J. Pier, A. Pope, M. Richmond, C. Rockosi, R. Scranton, R. Sheth, A. Stebbins, C. Stoughton, I. Szapudi, D. Tucker, D. Vanden Berk, B. Yanny, D. York Comments: SDSS data and ppt figures available at this http URL - 36 PRD pages, 25 figs. Belongs together with astro-ph/0608635 and astro-ph/0608636 We measure the large-scale real-space power spectrum P(k) using luminous red galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS) and use this measurement to sharpen constraints on cosmological parameters from the Wilkinson Microwave Anisotropy Probe (WMAP). We employ a matrix-based power spectrum estimation method using Pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 20 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.01h/Mpc < k < 0.2h/Mpc. Results from the LRG and main galaxy samples are consistent, with the former providing higher signal-to-noise. Our results are robust to omitting angular and radial density fluctuations and are consistent between different parts of the sky. They provide a striking confirmation of the predicted large-scale LCDM power spectrum. Combining only SDSS LRG and WMAP data places robust constraints on many cosmological parameters that complement prior analyses of multiple data sets. The LRGs provide independent cross-checks on Om and the baryon fraction in good agreement with WMAP. Within the context of flat LCDM models, our LRG measurements complement WMAP by sharpening the constraints on the matter density, the neutrino density and the tensor amplitude by about a factor of two, giving Omega_m=0.24+-0.02 (1 sigma), sum m_nu < 0.9 eV (95%) and r<0.3 (95%). Baryon oscillations are clearly detected and provide a robust measurement of the comoving distance to the median survey redshift z=0.35 independent of curvature and dark energy properties. Within the LCDM framework, our power spectrum measurement improves the evidence for spatial flatness, sharpening the curvature constraint Omega_tot=1.05+-0.05 from WMAP alone to Omega_tot=1.003+-0.010. Assuming Omega_tot=1, the equation of state parameter is constrained to w=-0.94+-0.09, indicating the potential for more ambitious future LRG measurements to provide precision tests of the nature of dark energy. All these constraints are essentially independent of scales k>0.1h/Mpc and associated nonlinear complications, yet agree well with more aggressive published analyses where nonlinear modeling is crucial. Full-text: PostScript, PDF, or Other formats Measuring the matter density using baryon oscillations in the SDSS Authors: Will J. Percival, Robert C. Nichol, Daniel J. Eisenstein, David H. Weinberg, Masataka Fukugita, Adrian C. Pope, Donald P. Schneider, Alex S. Szalay, Michael S. Vogeley, Idit Zehavi, Neta A. Bahcall, Jon Brinkmann, Andrew J. Connolly, Jon Loveday, Avery Meiksin Comments: 5 pages, 3 figures, submitted to ApJL We measure the cosmological matter density by observing the positions of baryon acoustic oscillations in the clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We jointly analyse the main galaxies and LRGs in the SDSS DR5 sample, using over half a million galaxies in total. The oscillations are detected with 99.74% confidence (3.0sigma assuming Gaussianity) compared to a smooth power spectrum. When combined with the observed scale of the peaks within the CMB, we find a best-fit value of Omega_m=0.256+0.029-0.024 (68% confidence interval), for a flat Lambda cosmology when marginalising over the Hubble parameter and the baryon density. This value of the matter density is derived from the locations of the baryon oscillations in the galaxy power spectrum and in the CMB, and does not include any information from the overall shape of the power spectra. This is an extremely clean cosmological measurement as the physics of the baryon acoustic oscillation production is well understood, and the positions of the oscillations are expected to be independent of systematics such as galaxy bias. Full-text: PostScript, PDF, or Other formats The shape of the SDSS DR5 galaxy power spectrum Authors: Will J. Percival, Robert C. Nichol, Daniel J. Eisenstein, Joshua A. Frieman, Masataka Fukugita, Jon Loveday, Adrian C. Pope, Donald P. Schneider, Alex S. Szalay, Max Tegmark, Michael S. Vogeley, David H. Weinberg, Idit Zehavi, Neta A. Bahcall, Jon Brinkmann, Andrew J. Connolly, Avery Meiksin Comments: 20 pages, 19 figures, submitted to ApJ We present a Fourier analysis of the clustering of galaxies in the combined Main galaxy and Luminous Red Galaxy (LRG) Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) sample. The aim of our analysis is to consider how well we can measure the cosmological matter density using the signature of the horizon at matter-radiation equality embedded in the large-scale power spectrum. The new data constrains the power spectrum on scales 100--600h^-1Mpc with significantly higher precision than previous analyses of just the SDSS Main galaxies, due to our larger sample and the inclusion of the LRGs. This improvement means that we can now reveal a discrepancy between the shape of the measured power and linear CDM models on scales 0.01<k<0.15hMpc^-1, with linear model fits favouring a lower matter density (Omega_m=0.22+/-0.04) on scales 0.01<k<0.06hMpc^-1 and a higher matter density (Omega_m=0.32+/-0.01) when smaller scales are included, assuming a flat LCDM model with h=0.73 and n_s=0.96. This discrepancy could be explained by scale-dependent bias and, by analysing subsamples of galaxies, we find that the ratio of small-scale to large-scale power increases with galaxy luminosity, so all of the SDSS galaxies cannot trace the same power spectrum shape over 0.01<k<0.2hMpc^-1. However, the data are insufficient to clearly show a luminosity-dependent change in the largest scale at which a significant increase in clustering is observed, although they do not rule out such an effect. Significant scale-dependent galaxy bias on large-scales, which changes with the r-band luminosity of the galaxies, could potentially explain differences in our Omega_m estimates and differences previously observed between 2dFGRS and SDSS power spectra and the resulting parameter constraints. Full-text: PostScript, PDF, or Other formats The Shear TEsting Programme 2: Factors affecting high precision weak lensing analyses Authors: Richard Massey, Catherine Heymans, Joel Berge, Gary Bernstein, Sarah Bridle, Douglas Clowe, Hakon Dahle, Richard Ellis, Thomas Erben, Marco Hetterscheidt, F. William High, Christopher Hirata, Henk Hoekstra, Patrick Hudelot, Mike Jarvis, David Johnston, Konrad Kuijken, Vera Margoniner, Rachel Mandelbaum, Yannick Mellier, Reiko Nakajima, Stephane Paulin-Henriksson, Molly Peeples, Chris Roat, Alexandre Refregier, Jason Rhodes, Tim Schrabback, Mischa Schirmer, Uros Seljak, Elisabetta Semboloni, Ludovic Van Waerbeke Comments: 27 pages, 10 figures, MNRAS submitted The Shear TEsting Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak lensing measurement, in preparation for the next generation of wide-field surveys. We review sixteen current and emerging shear measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known shear signal. We determine the common features of algorithms that most successfully recover the input parameters. We achieve previously unattained discriminatory precision in our analysis, via a combination of more extensive simulations, and pairs of galaxy images that have been rotated with respect to each other, thus removing noise from their intrinsic ellipticities. The robustness of our simulation approach is also confirmed by testing the relative calibration of methods on real data. Weak lensing measurement has improved since the first STEP paper. Several methods now consistently achieve better than 2% precision, and are still being developed. However, the simulations can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative shear calibration bias: not least because this can not be internally calibrated with real data. We determine which galaxy populations are responsible and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. We have isolated several previously unrecognised aspects of galaxy shape measurement, in which focussed development could provide further progress towards the sub-percent level of precision desired for future surveys. [ABRIDGED] Full-text: PostScript, PDF, or Other formats