Wednesday.
1404.3724
Bent by baryons: the low mass galaxy-halo relation
Sawala, Frenk, … Navarro, Bower, et al
The relation between galaxies and DM haloes is important for evaluating theoretical predictions of structure formation and galaxy formation physics. Show that the widely used method of abundance matching based on DM only simulations fails at the low mass end because two of its underlying assumptions are broken: only a small fraction of low mass (below 1e9.5 Msun) haloes host a visible galaxy, and haloes grow at a lower rate due to the effect of baryons. In this regime, reliance on DM only simulations for abundance matching is neither accurate nor self-consistent. Find that the reported discrepancy between observational estimates of the halo masses of dwarf galaxies and the values predicted by abundance matching does not point to a failure of LCDM, but simply to a failure to account for baryonic effects. Results also imply that the Local Group contains only a few hundred observable galaxies in contrast with the thousands of faint dwarfs that abundance matching would suggest. Show how relations derived from abundance matching can be corrected, so that they can be used self-consistently to calibrate models of galaxy formation.
1404.3725
Constraining primordial non-gaussianity with moments of the large scale density field
Mao, … Scoccimarro, et al
Use N-body sims to investigate whether measurements of large-scale structure can yield constraints on primordial non-Gaussianity. Measure the variance, skewness, and kurtosis of the evolved density field from simulations with Gaussian and 3 different non-Gaussian ICs: a local model with f_NL=100, an equilateral model with f_NL=-400, and an orthogonal model with f_NL=-400. Show that the moments of the DM density field differ significantly between Gaussian and non-Gaussian models. Also make the measurements on mock galaxy catalogs that contain galaxies with clustering properties similar to those of LRGs. Find that, in the case of skewness and kurtosis, galaxy bias reduces the detectability of non-Gaussianity, though still able to clearly discriminate between different models in the simulation volume. In the case of the variance, galaxy bias greatly amplifies the detectability of non-Gaussianity. In all cases, find that z distortions do not significantly affect the detectability. When restricted to measurements of volumes equivalent to SDSS-II or BOSS samples, the probability of detecting a departure from the Gaussian model is high by using measurements of the variance, but very low by using only skewness and kurtosis measurements. Find that skewness and kurtosis measurements are never likely to yield useful constraints on primordial non-Gaussianity, but future surveys should be large enough to place meaningful constraints using measurements of the galaxy variance.
1404.3730
Tensor-induced B modes with no temperature fluctuations
Kamionkowski, Dai, Jeong
The recent indications for r~=0.2 from BICEP2 measurements of CMB B-mode polarization present some tension with upper limits r<~0.1 from CMB temperature fluctuations. Point out that tensor perturbations can induce B modes in the CMB polarization without inducing any temperature fluctuations nor E-mode polarization whatsoever, but only, at the expense of violating the Copernican principle. Present this mathematical possibility as a new ingredient for the model-builder's toolkit in case the tension between B modes and temperature fluctuations cannot be resolved with more conventional ideas.
1404.3742
A 2.5% measurement of the growth rate from small-scale redshift space clustering of SDSS-III CMASS galaxies
Reid, Seo, Leauthaud, Tinker, White
Perform the fit to the anisotropic clustering of SDSS-III CMASS DR10 galaxies on scales of ~0.8 - 32 Mpc/h. A standard halo occupation distribution model evaluated near the best fit Planck LCDM cosmology provides a good fit to the observed anisotropic clustering, and implies a normalization for the peculiar velocity field of M~2e13 Msun/h haloes of f*sigma8(z=0.57)=0.450 pm 0.011. Since this constraint includes both quasi-linear and NL scales, it should severely constrain modified gravity models that enhance pairwise infall velocities on these scales. Though model dependent, measurement represents a factor of 2.5 improvement in precision over the analysis of DR11 on large scales, f*sigma8(z=0.57)=0.446pm0.028, and is the tightest single constraint on the growth rate of cosmic structure to date. Measurement is consistent with the Planck LCDM prediction of 0.48pm0.010 at the ~1.9 sigma level. Assuming a halo mass function evaluated at the best fit Planck cosmology, also find that 10% of CMASS galaxies are satellites in haloes of mass M~6e13 Msun/h. While none of the tests and model generalization indicate systematic errors due to an insufficiently detailed model of the galaxy-halo connection, the precision of these first results warrant further investigation into the modeling uncertainties and degeneracies with cosmological parameters.
1404.3799
The 6dF galaxy velocity survey: cosmological constraints from the velocity power spectrum
Johnson, Blake, et al
The scale-dependent measurements of the normalized growth rate of structure f*sigma_8(k,z=0) using only the peculiar motions of galaxies. Use data from the 6dFGSv together with a newly-compiled sample of z<0.07 type Ia SNe. Constrain the growth rate in a series of Delta k ~ 0.03 h/Mpc bins to ~35 precision, including a measurement on scales >300Mpc/h, which represents the largest-scale growth rate measurement to date. Find no evidence for a scale dependence in the growth rate, or any statistically significant variation from the growth rate as predicted by the Planck cosmology. Bringing all the scales together, determine the normalized growth rate at z=0 to ~15 in a matter independent of galaxy bias and in excellent agreement with the constraint from the measurements of z-space distortions from 6dFGS. Pay attention to systematic errors. Point out that the intrinsic scatter present in Fundamental-Plane and Tully-Fisher relations is only Gaussian in logarithmic distance units; wrongly assuming it is Gaussian in linear (velocity) units can bias cosmological constraints. Also analytically marginalize over zero-point errors in distance indicators, validate the accuracy of all the constraints using numerical simulations, and demonstrate how to combine different (correlated) velocity surveys using a matrix 'hyper-parmeter' analysis. Current and forthcoming peculiar velocity surveys will allow to understand in detail the growth of structure in the low-z universe, providing strong constraints on the nature of DE.
No comments:
Post a Comment