1509.07498
Void alignment and density profile applied to measuring cosmological parameters
Dai
Study the orientation and density profiles of the cosmological voids with SDSS10 data. Using voids to test Alcock-Paczynski effect has been proposed and tested in both simulations and actual SDSS data. Previous observations imply that there exist an empirical stretching factor which plays an important role in the voids' orientation. Simulations indicate that this empirical stretching factor is caused by the void galaxies' peculiar velocities. Recently Hamaus et al. found that voids' density profiles are universal and their average velocities satisfy linear theory very well. In this article, first confirm that the stretching effect exists using independent analysis. Then apply the universal density profile to measure the cosmo parameters. Find that the void density profile can be a tool to measure the cosmo parameters.
1509.07501
Cosmological hints of modified gravity?
Di Valentino, Melchiorri, Silk
The recent measurements of CMB temperature and polarization anisotropies made by Planck have provided impressive confirmation of the LCDM cosmo model. However, interesting hints of slight deviations from LCDM have been found, including a 95% CL preference for a "modified gravity" structure formation scenario. IN this paper, confirm the preference for a modified gravity scenario from Planck 2015 data, find that modified gravity solves the so-called A_lens anomaly in the CMB angular spectrum, and constraints the amplitude of matter density fluctuations to sigma8=0.815±0.05, in better agreement with WL constraints. Moreover, find a lower value for the reionization optical depth of tau=0.059±0.020 (to be compared with the value of tau=0.079±0.017 obtained in the standard scenario), more consistent with recent optical and UV data. Check the stability of this result by considering possible degeneracies with other parameters, including the neutrino effective number, the running of the spectral index and the amount of primordial He. The indication for modified gravity is still present at ~95% CL, and could become more signifiant if lower values of tau were to be further confirmed by future cosmo and astrophysical data.
1509.07506
Density jumps near the viral radius of galaxy clusters
Patej, Loeb
Recent simulations have indicated that the DM haloes of galaxy clusters should feature steep density jumps near the viral radius. Since the member galaxies are expected to follow similar collisionless dynamics as the dark matter, the galaxy density profile should show such a feature as well. Examine the potential of current datasets to test this prediction by selecting cluster members for a sample of 56 low-z (0.1<z<0.3) galaxy clusters, constructing their projected number density profiles, and fitting them with two profiles, one with a steep density jump and one without. Additionally, investigate the presence of a jump using a non-parmaeteric spline approach. Find that some of these clusters show strong evidence for a model with a density jump. Discuss avenues for further analysis of the density jump with future datasets.
1509.07585
Probing promordial non-Gaussianity consistency relation with galaxy surveys
Yamauchi, Takahashi
With a radio continuum galaxy survey by SKA, a photometric galaxy survey by Euclid and their combination, forecast future constraints on primordial non-Gaussianity. Focus on the potential impact of local-type higher-order nonlinear parameters on the parameter estimation and particularly the confirmation of the inflationary consistency inequality Non-standard inflationary models, such as multi-field models, introduce the scale-dependent stochastic clustering of galaxies on large scales, which is a unique probe of mechanism for generating primordial density fluctuations. The Fisher matrix analysis indicates that a deep and wide survey provided by SKA is more advantageous to constrain tau_NL, while Euclid has a strong constraining power for f_NL due to the redshift information, suggesting that the joint analysis between them are quite essential to break the degeneracy between f_NL and tau_NL. The combination of full SKA and Euclid will achieve the precision level needed to confirm the consistency inequality even for f_NL~0.9 and tau_NL~8, though it is still hard for a single survey to confirm it when f_NL<1.5.
1509.07649
Cosmology with strong lensing systems
Cao, et al
Assemble a catalog of 118 SL systems from SLACS, BELLS, LSD and SL2S surveys and use them to constrain the cosmic EoS. In particular, consider 2 cases of DE phenomenology: XCDM model where DE is modeled by a a fluid with constant w EoS parameter and in Chevalier-Polanski-Linder (CPL) parameterization where w is allowed to evolve with redshift: w(z)=w0+w1(z/(1+z)). Assume spherically symmetric mass distribution in lensing galaxies, but relax the rigid assumption of SIS model in favor to more general power-law index gamma, also allowing it to evolve with redshifts gamma(z). Results from the XCDM cosmology show the agreement with values (concerning both w and gamma parameters) obtained by other authors. Go further and constrain the CPL parameters jointly with gamma(z). The resulting confidence regions for the parameters are much better than those obtained with a similar method in the past. They are also showing a trend of being complementary to the SNIa data. Analysis demonstrate that SL systems can be used to probe cosmo parameters like the cosmic EoS for DE. Moreover, they have a potential to judge whether the cosmic EoS evolved with time or not.
No comments:
Post a Comment