ترغب بنشر مسار تعليمي؟ اضغط هنا

Constraints on large scale inhomogeneities from WMAP-5 and SDSS: confrontation with recent observations

81   0   0.0 ( 0 )
 نشر من قبل Paul Hunt Dr
 تاريخ النشر 2009
  مجال البحث فيزياء
والبحث باللغة English
 تأليف Paul Hunt




اسأل ChatGPT حول البحث

Measurements of the SNe Ia Hubble diagram which suggest that the universe is accelerating due to the effect of dark energy may be biased because we are located in a 200-300 Mpc underdense void which is expanding 20-30% faster than the average rate. With the smaller global Hubble parameter, the WMAP-5 data on cosmic microwave background anisotropies can be fitted without requiring dark energy if there is some excess power in the spectrum of primordial perturbations on 100 Mpc scales. The SDSS data on galaxy clustering can also be fitted if there is a small component of hot dark matter in the form of 0.5 eV mass neutrinos. We show however that if the primordial fluctuations are gaussian, the expected variance of the Hubble parameter and the matter density are far too small to allow such a large local void. Nevertheless many such large voids have been identified in the SDSS LRG survey in a search for the late-ISW effect due to dark energy. The observed CMB temperature decrements imply that they are nearly empty, thus these real voids too are in gross conflict with the concordance LCDM model. The recently observed high peculiar velocity flow presents another challenge for the model. Therefore whether a large local void actually exists must be tested through observations and cannot be dismissed a priori.



قيم البحث

اقرأ أيضاً

We present a Gaussianity analysis of the WMAP 5-year Cosmic Microwave Background (CMB) temperature anisotropy data maps. We use several third order estimators based on the spherical Mexican hat wavelet. We impose constraints on the local non-linear c oupling parameter fnl using well motivated non-Gaussian simulations. We analyse the WMAP maps at resolution of 6.9 arcmin for the Q, V, and W frequency bands. We use the KQ75 mask recommended by the WMAP team which masks out 28% of the sky. The wavelet coefficients are evaluated at 10 different scales from 6.9 to 150 arcmin. With these coefficients we compute the third order estimators which are used to perform a chi-squared analysis. The chi-squared statistic is used to test the Gaussianity of the WMAP data as well as to constrain the fnl parameter. Our results indicate that the WMAP data are compatible with the Gaussian simulations, and the fnl parameter is constrained to -8 < fnl < +111 at 95% CL for the combined V+W map. This value has been corrected for the presence of undetected point sources, which add a positive contribution of Delta_fnl = 3+-5 in the V+W map. Our results are very similar to those obtained by Komatsu et al (2008) using the bispectrum.
We measure cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a ``vanilla flat adiabatic L ambda-CDM model without tilt (n=1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1 sigma constraints on the Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.
293 - Ying Zu 2012
We derive constraints on the matter density Om and the amplitude of matter clustering sig8 from measurements of large scale weak lensing (projected separation R=5-30hmpc) by clusters in the Sloan Digital Sky Survey MaxBCG catalog. The weak lensing si gnal is proportional to the product of Om and the cluster-mass correlation function xicm. With the relation between optical richness and cluster mass constrained by the observed cluster number counts, the predicted lensing signal increases with increasing Om or sig8, with mild additional dependence on the assumed scatter between richness and mass. The dependence of the signal on scale and richness partly breaks the degeneracies among these parameters. We incorporate external priors on the richness-mass scatter from comparisons to X-ray data and on the shape of the matter power spectrum from galaxy clustering, and we test our adopted model for xicm against N-body simulations. Using a Bayesian approach with minimal restrictive priors, we find sig8(Om/0.325)^{0.501}=0.828 +/- 0.049, with marginalized constraints of Om=0.325_{-0.067}^{+0.086} and sig8=0.828_{-0.097}^{+0.111}, consistent with constraints from other MaxBCG studies that use weak lensing measurements on small scales (R<=2hmpc). The (Om,sig8) constraint is consistent with and orthogonal to the one inferred from WMAP CMB data, reflecting agreement with the structure growth predicted by GR for an LCDM cosmological model. A joint constraint assuming LCDM yields Om=0.298 +/- 0.020 and sig8=0.831 +/- 0.020. Our cosmological parameter errors are dominated by the statistical uncertainties of the large scale weak lensing measurements, which should shrink sharply with current and future imaging surveys.
127 - Kengo Iwata , Chul-Moon Yoo 2014
We investigate the effect of small scale inhomogeneities on standard candle observations, such as type Ia supernovae (SNe) observations. Existence of the small scale inhomogeneities may cause a tension between SNe observations and other observations with larger diameter sources, such as the cosmic microwave background (CMB) observation. To clarify the impact of the small scale inhomogeneities, we use the Dyer-Roeder approach. We determined the smoothness parameter $alpha(z)$ as a function of the redshift $z$ so as to compensate the deviation of cosmological parameters for SNe from those for CMB. The range of the deviation which can be compensated by the smoothness parameter $alpha(z)$ satisfying $0leqalpha(z)leq1$ is reported. Our result suggests that the tension may give us the information of the small scale inhomogeneities through the smoothness parameter.
183 - L.A. Popa , A. Vasile 2008
In this paper we set bounds on the radiation content of the Universe and neutrino properties by using the WMAP-5 year CMB measurements complemented with most of the existing CMB and LSS data (WMAP5+All),imposing also self-consistent BBN constraints o n the primordial helium abundance. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter and the variation of the relativistic degrees of freedom, due to possible other physical processes occurred between BBN and structure formation epochs. We find that WMAP5+All data provides strong bounds on helium mass fraction and neutrino degeneracy parameter that rivals the similar bounds obtained from the conservative analysis of the present data on helium abundance. We also find a strong correlation between the matter energy density and the redshift of matter-radiation equality, z_re, showing that we observe non-zero equivalent number of relativistic neutrinos mainly via the change of the of z_re, rather than via neutrino anisotropic stress claimed by the WMAP team. We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivities by the future Planck satellite will reduce the errors on these parameters down to values fully consistent with the BBN bounds.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا