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Munch: Monday, September 18, 2006 |
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usual time and place: 12:30, 6th floor conference room |
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11 Sep 2006 |
This week: tension between cosmological probes? The WMAP first year data release was widely supported by results from other cosmological probes, such as weak lensing cosmic shear, large scale structure from galaxy surveys, and Sunyaev-Zeldovitch (SZ) power spectrum measurements from small scale measurements of the CMB, while galaxy clusters tended to favor a lower level of mass fluctuations and density. With the release of the WMAP 3 year data, the agreement of the first 3 probes is now questionable by 2-sigma or more in the literature, and galaxy cluster results now agree with WMAP. What should we think? As a warning, the list of papers below is rather long, and not particularly recent, so in red I have included some guidance. WMAP 3 year results: Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for CosmologyAuthors: D. N. Spergel, R. Bean, O. Dore', M. R. Nolta, C. L. Bennett, G. Hinshaw, N. Jarosik, E. Komatsu, L. Page, H. V. Peiris, L. Verde, C. Barnes, M. Halpern, R. S. Hill, A. Kogut, M. Limon, S. S. Meyer, N. Odegard, G. S. Tucker, J. L. Weiland, E. Wollack, E. L. WrightComments: 89 pages, 28 figures, submitted to ApJ A simple cosmological model with only six parameters (matter density, Omega_m h^2, baryon density, Omega_b h^2, Hubble Constant, H_0, amplitude of fluctuations, sigma_8, optical depth, tau, and a slope for the scalar perturbation spectrum, n_s) fits not only the three year WMAP temperature and polarization data, but also small scale CMB data, light element abundances, large-scale structure observations, and the supernova luminosity/distance relationship. Using WMAP data only, the best fit values for cosmological parameters for the power-law flat LCDM model are (Omega_m h^2, Omega_b h^2, h, n_s, tau, sigma_8) = (0.127+0.007-0.013, 0.0223+0.0007-0.0009, 0.73 +- 0.03, 0.951+0.015-0.019, 0.09 +- 0.03, 0.74+0.05-0.06). The three year data dramatically shrink the allowed volume in this six-dimensional parameter space. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, the WMAP data_alone_ require dark matter, and a spectral index that is significantly less than the Harrison-Zel'dovich-Peebles scale-invariant spectrum (n_s=1,r=0). Models that suppress large-scale power through a running spectral index or a large-scale cut-off in the power spectrum are a slightly better fit to the WMAP and small scale CMB data than the power-law LCDM model (Delta chi^2 = 3) The combination of WMAP and other astronomical data yields significant constraints on the geometry of the universe, the equation of state of the dark energy, the gravitational wave energy density, and neutrino properties. Consistent with the predictions of simple inflationary theories, we detect no significant deviations from Gaussianity in the CMB maps. Full-text: PostScript, PDF, or Other formatsCosmological Constraints from the SDSS Luminous Red GalaxiesAuthors: 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. YorkComments: 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. Full-text: PostScript, PDF, or Other formatsCosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraintsAuthors: Uros Seljak, Anze Slosar, Patrick McDonaldComments: 11 pages, 4 figures; v2: A numerical error found and corrected, significantly affects constraints on number of neutrino families and sterile neutrino mass, other constraints unaffected We combine the Ly-alpha forest power spectrum (LYA) from the Sloan Digital Sky Survey (SDSS) and high resolution spectra with cosmic microwave background (CMB) including 3-year WMAP, and supernovae (SN) and galaxy clustering constraints to derive new constraints on cosmological parameters. The existing LYA power spectrum analysis is supplemented by constraints on the mean flux decrement derived using a principle component analysis for quasar continua, which improves the LYA constraints on the linear power. We find some tension between the WMAP3 and LYA power spectrum amplitudes, at the ~2 sigma level, which is partially alleviated by the inclusion of other observations: we find \sigma_8=0.85\pm 0.02 compared to sigma_8=0.80 \pm 0.03 without LYA. For the slope we find ns=0.965\pm0.012. We find no evidence for the running of the spectral index in the combined analysis, dn/dln k=-(1.5\pm 1.2) x 10^{-2}, in agreement with inflation. The limits on the sum of neutrino masses are significantly improved: $\sum m_{\nu}<0.17\eV$ at 95% (<0.32eV at 99.9%). This result, when combined with atmospheric and solar neutrino mixing constraints, requires that the neutrino masses cannot be degenerate, m_3/m_1>1.3 (95% c.l.). Assuming a thermalized fourth neutrino we find m_s<0.26\eV at 95% c.l. and such neutrino cannot be an explanation for the LSND results. In the limits of massless neutrinos we obtain the effective number of neutrinos N_\nu^{\rm eff}=5.3^{+0.4}_{-0.6}{}^{+2.1}_{-1.7}{}^{+3.8}_{-2.5} and N_\nu^{\rm eff}=3 is allowed only at 3-sigma. The constraint on the dark energy equation of state is w=-1.04\pm 0.06. The constraint on curvature is Omega_k=-0.003\pm 0.006. Cosmic strings limits are G\mu <2.3 x 10^{-7} at 95% c.l. and correlated isocurvature models are also tightly constrained. Full-text: PostScript, PDF, or Other formatsWeak lensing tension with WMAP? You may want to read the abstracts only for most of these, and section 5.8 of the Massey paper. The Semboloni paper is short, relevent, and worth reading as a stand alone even for non-specialists. First cosmic shear results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy SurveyAuthors: H. Hoekstra, Y. Mellier, L. van Waerbeke, E. Semboloni, L. Fu, M.J. Hudson, L.C. Parker, I. Tereno, K. BenabedComments: Submitted to ApJ We present the first measurements of the weak gravitational lensing signal induced by the large scale mass distribution from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in this analysis are from the Wide Synoptic Survey, which aims to image ~170 square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i' data spread over two of the three survey fields. These data are of excellent quality and the results bode well for the remainder of the survey: we do not detect a significant `B'-mode, suggesting that residual systematics are negligible at the current level of accuracy. Assuming a Cold Dark Matter model and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift distribution and systematics, we constrain sigma_8, the amplitude of the matter power spectrum. At a fiducial matter density Omega_m=0.3 we find sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous studies. Combination of our results with those from the Deep component of the CFHTLS enables us to place a constraint on a constant equation of state for the dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68% confidence. Full-text: PostScript, PDF, or Other formatsCosmic Shear Analysis with CFHTLS Deep dataAuthors: E. Semboloni, Y. Mellier, L. van Waerbeke, H. Hoekstra, I. Tereno, K. Benabed, S. Gwyn, L. Fu, M.J. Hudson, R. Maoli, L. ParkerComments: 14 pages, 16 figures, accepted A&A We present the first cosmic shear measurements obtained from the T0001 release of the Canada-France-Hawaii Telescope Legacy Survey. The data set covers three uncorrelated patches (D1, D3 and D4) of one square degree each observed in u*, g', r', i' and z' bands, out to i'=25.5. The depth and the multicolored observations done in deep fields enable several data quality controls. The lensing signal is detected in both r' and i' bands and shows similar amplitude and slope in both filters. B-modes are found to be statistically zero at all scales. Using multi-color information, we derived a photometric redshift for each galaxy and separate the sample into medium and high-z galaxies. A stronger shear signal is detected from the high-z subsample than from the low-z subsample, as expected from weak lensing tomography. While further work is needed to model the effects of errors in the photometric redshifts, this results suggests that it will be possible to obtain constraints on the growth of dark matter fluctuations with lensing wide field surveys. The various quality tests and analysis discussed in this work demonstrate that MegaPrime/Megacam instrument produces excellent quality data. The combined Deep and Wide surveys give sigma_8= 0.89 pm 0.06 assuming the Peacock & Dodds non-linear scheme and sigma_8=0.86 pm 0.05 for the halo fitting model and Omega_m=0.3. We assumed a Cold Dark Matter model with flat geometry. Systematics, Hubble constant and redshift uncertainties have been marginalized over. Using only data from the Deep survey, the 1 sigma upper bound for w_0, the constant equation of state parameter is w_0 < -0.8. Full-text: PostScript, PDF, or Other formatsThe Shear TEsting Programme 2: Factors affecting high precision weak lensing analysesAuthors: 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 WaerbekeComments: 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. Full-text: PostScript, PDF, or Other formatsAccurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep SurveyAuthors: O. Ilbert, S. Arnouts, H.J. McCracken, M. Bolzonella, E. Bertin, O. Le Fevre, Y. Mellier, G. Zamorani, R. Pello, A. Iovino, L. Tresse, D. Bottini, B. Garilli, V. Le Brun, D. Maccagni, J.P. Picat, R. Scaramella, M. Scodeggio, G. Vettolani, A. Zanichelli, C. Adami, S. Bardelli, A. Cappi, S. Charlot, P. Ciliegi, T. Contini, O. Cucciati, S. Foucaud, P. Franzetti, I. Gavignaud, L. Guzzo, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, A. Pollo, L. Pozzetti, M. Radovich, E. Zucca, M. Bondi, A. Bongiorno, G. Busarello, S. De La Torre, L. Gregorini, F. Lamareille, G. Mathez, P. Merluzzi, V. Ripepi, D. Rizzo, D. VerganiComments: 19 pages, 17 figures, submitted to A&A. The photometric redshifts described in this paper will be made publicly available from 1st may 2006 at this http URL and this http URL We present photometric redshifts for an uniquely large and deep sample of 522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241 spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a calibration to derive these photometric redshifts. We devise a robust calibration method which removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. For a sample selected at i'_{AB}<24, we reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of catastrophic error. The reliability of our photometric redshifts is lower for fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%, 5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We find that the photometric redshifts of starburst galaxies in our sample are less reliable: although these galaxies represent only 18% of the spectroscopic sample they are responsible for 54% of the catastrophic errors. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at i'_{AB}<24. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is already present on fields of 0.8 deg^2. Full-text: PostScript, PDF, or Other formatsCosmic variance of weak lensing surveys in the non-linear regimeAuthors: Elisabetta Semboloni, Ludovic van Waerbeke, Catherine Heymans, Takashi Hamana, Stephane Colombi, Martin White, Yannick MellierComments: 5 pages, 6 figures. Submitted to MNRAS The results from weak gravitational lensing analyses are subject to a cosmic variance error term that has previously been estimated assuming Gaussian statistics. In this letter we address the issue of estimating cosmic variance errors for weak lensing surveys in the non-linear regime. Using standard cold dark matter model ray-tracing simulations for different survey redshifts z_s, we determine the variance of the two-point shear correlation function measured across 64 independent lines of sight. We compare the measured variance to the variance expected from a random Gaussian field and derive a redshift-dependent non-Gaussian calibration relation. We find that the ratio can be as high as ~30 for a survey with source redshift z_s ~ 0.5 and ~10 for z_s ~ 1. The transition scale theta_c above which the ratio is consistent with unity, is found to be theta_c ~ 20 arcmin for z_s ~ 0.5 and theta_c ~ 10 arcmin for z_s ~ 1. We provide fitting formula to our results permitting the estimation of non-Gaussian cosmic variance errors for any weak lensing analysis, and discuss the impact on current and future surveys. A more extensive set of simulations will however be required to investigate the dependence of our results on cosmology. Full-text: PostScript, PDF, or Other formatshow about the SZ effect? Note that the last sentence of the abstract of Bond et al. is pre WMAP 3 year; the disagreement is a lot worse now. The Douspis paper argues for a solution... The Sunyaev-Zeldovich effect in CMB-calibrated theories applied to the Cosmic Background Imager anisotropy power at l > 2000Authors: J. R. Bond (CITA), C. R. Contaldi (CITA), U.-L. Pen (CITA), D. Pogosyan (U. of Alberta), S. Prunet (IAP Paris), M. I. Ruetalo (CITA), J. W. Wadsley (McMaster U.), P. Zhang (CITA), B. S. Mason (Caltech), S. T. Myers (NRAO), T. J. Pearson (Caltech), A. C. S. Readhead (Caltech), J. L. Sievers (Caltech), P. S. Udomprasert (Caltech)Comments: Accepted by The Astrophysical Journal; 17 pages including 12 color figures. v2 matches accepted version. Additional information at this http URL Journal-ref: Astrophys.J. 626 (2005) 12 We discuss the nature of the possible high-l excess in the Cosmic Microwave Background (CMB) anisotropy power spectrum observed by the Cosmic Background Imager (CBI). We probe the angular structure of the excess in the CBI deep fields and investigate whether it could be due to the scattering of CMB photons by hot electrons within clusters, the Sunyaev-Zeldovich (SZ) effect. We estimate the density fluctuation parameters for amplitude, sigma_8, and shape, Gamma, from CMB primary anisotropy data and other cosmological data. We use the results of two separate hydrodynamical codes for Lambda-CDM cosmologies, consistent with the allowed sigma_8 and Gamma values, to quantify the expected contribution from the SZ effect to the bandpowers of the CBI experiment and pass simulated SZ effect maps through our CBI analysis pipeline. The result is very sensitive to the value of sigma_8, and is roughly consistent with the observed power if sigma_8 ~ 1. We conclude that the CBI anomaly could be a result of the SZ effect for the class of Lambda-CDM concordance models if sigma_8 is in the upper range of values allowed by current CMB and Large Scale Structure (LSS) data. Full-text: PostScript, PDF, or Other formatsSmall scale contributions to CMB: A coherent analysisAuthors: Marian Douspis (IAS, LATT), Nabila Aghanim (IAS), Mathieu Langer (IAS)Comments: 9 pages We reanalyse Cosmic Microwave Background data from experiments probing both large and small scales. We assume that measured anisotropies are due not only to primary fluctuations but also, especially at small scales, to secondary effects (namely the Sunyaev-Zel'dovich effect) and possible point source contaminations. We first consider primary and secondary anisotropies only. For the first time in such analyses, the cosmological dependence of secondary fluctuations is fully taken into account. We show in that case that a higher value of the normalisation $\sigma\_8$ is preferred, as found by previous studies, but also higher values of the optical depth $\tau$ and power spectrum index $n\_s$ are needed. In the second part of our analysis, we further include possible contaminations from unresolved and unremoved point sources. Under these considerations, we discuss the effects on the cosmological parameters. We further obtain the best combination of relative contributions of the three kinds of sources to the measured microwave power on small scales at each frequency. Our method allows us to simultaneously obtain cosmological parameters and explain the so-called small scale power excess in a consistent way. Full-text: PostScript, PDF, or Other formatshow do clusters compare to wmap? Clusters have always agreed with WMAP 3 year, again the abstracts alone may be all you need to read... Constraining amplitude and slope of the mass fluctuation spectrum using cluster baryon mass functionAuthors: A. Voevodkin, A. VikhlininComments: 11 pages, ApJ in press. Minor changes to synchronize with the accepted version Journal-ref: Astrophys.J. 601 (2004) 610-620 We derive the baryon mass function for a complete sample of low-redshift clusters and argue that it is an excellent proxy for the total mass function if the ratio f_b=M_b/M_tot in all clusters is close to its universal value, Omega_b/Omega_M. Under this assumption, the baryon mass function can be used to constrain the amplitude and slope of the density fluctuations power spectrum on cluster scales. This method does not use observational determinations of the total mass and thus bypasses major uncertainties in the traditional analyses based on the X-ray temperature function. However, it is sensitive to possible systematic variations of the baryon fraction as a function of cluster mass. Adapting a weak dependence f_b(M) suggested by observations and numerical simulations by Bialek et al., we derive sigma_8=0.72+-0.04 and the shape parameter Omega_M*h=0.13+-0.07, in good agreement with a number of independent methods. We discuss the sensitivity of these values to other cosmological parameters and to different assumptions about variations in f_b. Full-text: PostScript, PDF, or Other formatsOn determining the cluster abundance normalizationAuthors: E. Pierpaoli, S. Borgani, D. Scott, M. WhiteComments: 15 pages, minor changes to match accepted version Journal-ref: Mon.Not.Roy.Astron.Soc. 342 (2003) 163 Different determinations currently suggest scattered values for the power spectrum normalization on the scale of galaxy clusters, sigma_8. Here we concentrate on the constraints coming from the X-ray temperature and luminosity functions (XTF and XLF), and investigate several possible sources of discrepancies in the results. We conclude that the main source of error in both methods is the scaling relation involved, in particular the way its intrinsic scatter and systematic normalization are treated. For temperature derived constraints, we use a sample adapted from HIFLUGCS, and test for several sources of systematic error. We parameterize the mass-temperature relation with an overall factor T_ast, with 1.5 \le T_ast \le 1.9. After marginalising over the range of T_ast, we obtain a 68 per cent confidence range of sigma_8=0.77^{+0.05}_{-0.04} for a standard LambdaCDM model. For luminosity derived constraints we use the XLF from the REFLEX survey and explore how sensitive the final results are on the details of the mass-luminosity, M-L, conversion. Assuming a uniform systematic uncertainty of +/-20 per cent in the amplitude of the mass-luminosity relation by Reiprich and Bohringer, we derive sigma_8=0.79^{+0.06}_{-0.07} for the same standard LambdaCDM model. Although the XTF and XLF derived constraints agree very well with each other, we emphasize that such results can change by about 10--15 per cent, depending on how uncertainties in the L-T-M conversions are interpreted and included in the analysis. In order to achieve precision cosmology, with this probe, it is important to separate the uncertainty in the scaling relation into its intrinsic and overall normalization parts. Full-text: PostScript, PDF, or Other formatsCosmological Constraints from the Red-Sequence Cluster SurveyAuthors: Michael D. Gladders, H.K.C. Yee, Subhabrata Majumdar, L. Felipe Barrientos, Henk Hoekstra, Patrick B. Hall, Leopoldo InfanteComments: 18 pages, 4 figures, 3 tables [abridged] We present a first cosmological analysis of a refined cluster catalog from the Red-Sequence Cluster Survey (RCS). The input cluster sample is derived from 72.07 square degrees of imaging data [...] The catalog contains 956 clusters over 0.35<z<0.95, limited by cluster richness and richness error. The calibration of the survey images has been extensively cross-checked against publicly available Sloan Digital Sky Survey imaging [...] We analyze the cluster sample via a general self-calibration technique including scatter in the mass-richness relation [...]. We fit simultaneously for Omega_M and sigma_8, and four parameters describing the calibration of cluster richness to mass, its evolution with redshift, and scatter in the richness-mass relation. The principal goal of this general analysis is to establish the consistency (or lack thereof) between the fitted parameters (both cosmological and cluster mass observables) and available results on both from independent measures. From an unconstrained analysis, Omega_M and sigma_8 are 0.31+0.11-0.10 and 0.67+0.18-0.13 respectively. An analysis including Gaussian priors on the slope and zeropoint of the mass-richness relation gives very similar results: 0.30+0.12-0.11 and 0.70+0.27-0.15. Both analyses are in good agreement with the current literature. The parameters describing the mass-richness relation in the unconstrained fit are also eminently reasonable and agree with existing follow-up data on both the RCS-1 and other cluster samples. Our results directly demonstrate that future surveys (optical and otherwise), with much larger samples of clusters, can give constraints competitive with other probes of cosmology. Full-text: PostScript, PDF, or Other formatsHow about SDSS and 2dFGRS? The Gaztanaga paper provides a constraint on cosmology using galaxy surveys that is independent of WMAP... Statistical Analysis of Galaxy Surveys-II. The 3-point galaxy correlation function measured from the 2dFGRSAuthors: E.Gaztanaga (CSIC), P.Norberg (ETHZ), C.M.Baugh (Durham), D.J.Croton (MPA)Comments: 16 pages, 10 figures, minor changes, extended comparison to previous results, accepted for publication in MNRAS Journal-ref: Mon.Not.Roy.Astron.Soc. 364 (2005) 620-634 We present new results for the 3-point correlation function, \zeta, measured as a function of scale, luminosity and colour from the final version of the two-degree field galaxy redshift survey (2dFGRS). The reduced three point correlation function, Q_3 is estimated for different triangle shapes and sizes, employing a full covariance analysis. The form of Q_3 is consistent with the expectations for the \Lambda-cold dark matter model, confirming that the primary influence shaping the distribution of galaxies is gravitational instability acting on Gaussian primordial fluctuations. However, we find a clear offset in amplitude between Q_3 for galaxies and the predictions for the dark matter. We are able to rule out the scenario in which galaxies are unbiased tracers of the mass at the 9-sigma level. On weakly non-linear scales, we can interpret our results in terms of galaxy bias parameters. We find a linear bias term that is consistent with unity, b_1 = 0.93^{+0.10}_{-0.08} and a quadratic bias c_2 = b_2 /b_1 = -0.34^{+0.11}_{-0.08}. This is the first significant detection of a non-zero quadratic bias, indicating a small but important non-gravitational contribution to the three point function. Our estimate of the linear bias from the three point function is independent of the normalisation of underlying density fluctuations, so we can combine this with the measurement of the power spectrum of 2dFGRS galaxies to constrain the amplitude of matter fluctuations. We find that the rms linear theory variance in spheres of radius 8Mpc/h is \sigma_8 = 0.88^{+0.12}_{-0.10}, providing an independent confirmation of values derived from other techniques. On non-linear scales, where \xi>1, we find that Q_3 has a strong dependence on scale, colour and luminosity. Full-text: PostScript, PDF, or Other formatsThe Effect of Large-Scale Structure on the SDSS Galaxy Three-Point Correlation FunctionAuthors: R. C. Nichol (ICG Portsmouth), R. K. Sheth, Y. Suto, A. J. Gray, I. Kayo, R. H. Wechsler, F. Marin, G. Kulkarni, M. Blanton, A. J. Connolly, J. P. Gardner, B. Jain, C. J. Miller, A. W. Moore, A. Pope, J. Pun, D. Schneider, J. Schneider, A. Szalay, I. Szapudi, I. Zehavi, N. A. Bahcall, I. Csabai, J. BrinkmannComments: Accepted for publication in MNRAS Journal-ref: Mon.Not.Roy.Astron.Soc. 368 (2006) 1507-1514 We present measurements of the normalised redshift-space three-point correlation function (Q_z) of galaxies from the Sloan Digital Sky Survey (SDSS) main galaxy sample. We have applied our "npt" algorithm to both a volume-limited (36738 galaxies) and magnitude-limited sample (134741 galaxies) of SDSS galaxies, and find consistent results between the two samples, thus confirming the weak luminosity dependence of Q_z recently seen by other authors. We compare our results to other Q_z measurements in the literature and find it to be consistent within the full jack-knife error estimates. However, we find these errors are significantly increased by the presence of the ``Sloan Great Wall'' (at z ~ 0.08) within these two SDSS datasets, which changes the 3-point correlation function (3PCF) by 70% on large scales (s>=10h^-1 Mpc). If we exclude this supercluster, our observed Q_z is in better agreement with that obtained from the 2dFGRS by other authors, thus demonstrating the sensitivity of these higher-order correlation functions to large-scale structures in the Universe. This analysis highlights that the SDSS datasets used here are not ``fair samples'' of the Universe for the estimation of higher-order clustering statistics and larger volumes are required. We study the shape-dependence of Q_z(s,q,theta) as one expects this measurement to depend on scale if the large scale structure in the Universe has grown via gravitational instability from Gaussian initial conditions. On small scales (s <= 6h^-1 Mpc), we see some evidence for shape-dependence in Q_z, but at present our measurements are consistent with a constant within the errors (Q_z ~ 0.75 +/- 0.05). On scales >10h^-1 Mpc, we see considerable shape-dependence in Q_z. Full-text: PostScript, PDF, or Other formats |
Here is a list of anomalies in the neutrino sector (from Scott): 1] Why do you get different limits on N_\nu w/ SDSS and 2dF? Table 10 in Spergel et al 0603449 2] Why is there such a wide spread in the N_\nu constraints in general [e.g. between Spergel etal 2006 and Slejak et al 2006]? 3] Why does Tegmark 2004,2006 get no m_\nu constraint from CMB alone but Spergel 2006 and Fukugita do get one? 4] Why is the constraint on sterile mass looser than on the sum of the lightest 3 [see, e.g., Dodelson et al 2006 or Seljak et al 2006]? |
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