Cosmological redshift distortion: deceleration, bias and density parameters from future redshift surveys of galaxies

The observed two-point correlation functions of galaxies in redshift space become anisotropic due to the geometry of the universe as well as due to the presence of the peculiar velocity field. On the basis of linear perturbation theory, we expand the induced anisotropies of the correlation functions with respect to the redshift $z$, and obtain analytic formulae to infer the deceleration parameter $q_0$, the density parameter $\Omega_0$ and the derivative of the bias parameter $d\ln b/dz$ at $z=0$ in terms of the observable statistical quantities. The present method does not require any assumption of the shape and amplitude of the underlying fluctuation spectrum, and thus can be applied to future redshift surveys of galaxies including the Sloan Digital Sky Survey. We also evaluate quantitatively the systematic error in estimating the value of $\beta_0 \equiv \Omega_0^{0.6}/b$ from a galaxy redshift survey on the basis of a conventional estimator for $\beta_0$ which neglects both the geometrical distortion effect and the time evolution of the parameter $\beta(z)$. If the magnitude limit of the survey is as faint as 18.5 (in B-band) as in the case of the Sloan Digital Sky Survey, the systematic error ranges between -20% and 10% depending on the cosmological parameters. Although such systematic errors are smaller than the statistical errors in the current surveys, they will dominate the expected statistical error for future surveys.Comment: 9 pages, 5 figs, aastex, ApJ in press, replaced version includes minor correction

Velocity bias in a LCDM model

We use N-body simulations to study the velocity bias of dark matter halos, the difference in the velocity fields of dark matter and halos, in a flat low- density LCDM model. The high force, 2kpc/h, and mass, 10^9Msun/h, resolution allows dark matter halos to survive in very dense environments of groups and clusters making it possible to use halos as galaxy tracers. We find that the velocity bias pvb measured as a ratio of pairwise velocities of the halos to that of the dark matter evolves with time and depends on scale. At high redshifts (z ~5) halos move generally faster than the dark matter almost on all scales: pvb(r)~1.2, r>0.5Mpc/h. At later moments the bias decreases and gets below unity on scales less than r=5Mpc/h: pvb(r)~(0.6-0.8) at z=0. We find that the evolution of the pairwise velocity bias follows and probably is defined by the spatial antibias of the dark matter halos at small scales. One-point velocity bias b_v, defined as the ratio of the rms velocities of halos and dark matter, provides a more direct measure of the difference in velocities because it is less sensitive to the spatial bias. We analyze b_v in clusters of galaxies and find that halos are ``hotter'' than the dark matter: b_v=(1.2-1.3) for r=(0.2-0.8)r_vir, where r_vir is the virial radius. At larger radii, b_v decreases and approaches unity at r=(1-2)r_vir. We argue that dynamical friction may be responsible for this small positive velocity bias b_v>1 found in the central parts of clusters. We do not find significant difference in the velocity anisotropy of halos and the dark matter. The dark matter the velocity anisotropy can be approximated as beta(x)=0.15 +2x/(x^2+4), where x is measured in units of the virial radius.Comment: 13 pages, Latex, AASTeXv5 and natbi

Majorana spinors and extended Lorentz symmetry in four-dimensional theory

An extended local Lorentz symmetry in four-dimensional (4D) theory is considered. A source of this symmetry is a group of general linear transformations of four-component Majorana spinors GL(4,M) which is isomorphic to GL(4,R) and is the covering of an extended Lorentz group in a 6D Minkowski space M(3,3) including superluminal and scaling transformations. Physical space-time is assumed to be a 4D pseudo-Riemannian manifold. To connect the extended Lorentz symmetry in the M(3,3) space with the physical space-time, a fiber bundle over the 4D manifold is introduced with M(3,3) as a typical fiber. The action is constructed which is invariant with respect to both general 4D coordinate and local GL(4,M) spinor transformations. The components of the metric on the 6D fiber are expressed in terms of the 4D pseudo-Riemannian metric and two extra complex fields: 4D vector and scalar ones. These extra fields describe in the general case massive particles interacting with an extra U(1) gauge field and weakly interacting with ordinary particles, i.e. possessing properties of invisible (dark) matter.Comment: 24 page

Computer system for monitoring radiorepirometry data

System monitors expired breath patterns simultaneously from four small animals after they have been injected with carbon-14 substrates. It has revealed significant quantitative differences in oxidation patterns of glucose following such mild treatments of rats as a change in diet or environment

Mean age gradient and asymmetry in the star formation history of the Small Magellanic Cloud

We derive the star formation history in four regions of the Small Magellanic Cloud (SMC) using the deepest VI color-magnitude diagrams (CMDs) ever obtained for this galaxy. The images were obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope and are located at projected distances of 0.5-2 degrees from the SMC center, probing the main body and the wing of the galaxy. We derived the star-formation histories (SFH) of the four fields using two independent procedures to fit synthetic CMDs to the data. We compare the SFHs derived here with our earlier results for the SMC bar to create a deep pencil-beam survey of the global history of the central SMC. We find in all the six fields observed with HST a slow star formation pace from 13 to 5-7 Gyr ago, followed by a ~ 2-3 times higher activity. This is remarkable because dynamical models do not predict a strong influence of either the LMC or the Milky Way (MW) at that time. The level of the intermediate-age SFR enhancement systematically increases towards the center, resulting in a gradient in the mean age of the population, with the bar fields being systematically younger than the outer ones. Star formation over the most recent 500 Myr is strongly concentrated in the bar, the only exception being the area of the SMC wing. The strong current activity of the latter is likely driven by interaction with the LMC. At a given age, there is no significant difference in metallicity between the inner and outer fields, implying that metals are well mixed throughout the SMC. The age-metallicity relations we infer from our best fitting models are monotonically increasing with time, with no evidence of dips. This may argue against the major merger scenario proposed by Tsujimoto and Bekki 2009, although a minor merger cannot be ruled out.Comment: 30 pages, 16 figures, accepted for publication in Ap

The Effects of Age on Red Giant Metallicities Derived from the Near-Infrared Ca II Triplet

We have obtained spectra with resolution 2.5 Angstroms in the region 7500-9500 Angstroms for 116 red giants in 5 Galactic globular clusters and 6 old open clusters (5 with published metallicities, and one previously unmeasured). The signal-to-noise ranges from 20 to 85. We measure the equivalent widths of the infrared Ca II triplet absorption lines in each stars and compare to cluster metallicities taken from the literature. With globular cluster abundances on the Carretta & Gratton scale, and open cluster abundances taken from the compilation of Friel and collaborators, we find a linear relation between [Fe/H] and Ca II line strength spanning the range -2 < [Fe/H] < -0.2 and ages from 2.5 - 13 Gyr. No evidence for an age effect on the metallicity calibration is observed. Using this calibration, we find the metallicity of the old open cluster Trumpler 5 to be [Fe/H] = -0.56 +/-0.11. Considering the 10 clusters of known metallicity shifted to a common distance and reddening, we find that the additional metallicity error introduced by the variation of horizontal branch/red clump magnitude with metallicity and age is of order +/-0.05 dex, which can be neglected in comparison to the intrinsic scatter in our method. The results are discussed in the context of abundance determinations for red giants in Local Group galaxies.Comment: Accepted by MNRAS; 21 pages in LaTeX MNRAS style, 6 tables, 6 figure

Dependence of the Inner DM Profile on the Halo Mass

I compare the density profile of dark matter (DM) halos in cold dark matter (CDM) N-body simulations with 1 Mpc, 32 Mpc, 256 Mpc and 1024 Mpc box sizes. In dimensionless units the simulations differ only for the initial power spectrum of density perturbations. I compare the profiles when the most massive halos are composed of about 10^5 DM particles. The DM density profiles of the halos in the 1 Mpc box show systematically shallower cores with respect to the corresponding halos in the 32 Mpc simulation that have masses, M_{dm}, typical of the Milky Way and are fitted by a NFW profile. The DM density profiles of the halos in the 256 Mpc box are consistent with having steeper cores than the corresponding halos in the 32 Mpc simulation, but higher mass resolution simulations are needed to strengthen this result. Combined, these results indicate that the density profile of DM halos is not universal, presenting shallower cores in dwarf galaxies and steeper cores in clusters. Physically the result sustains the hypothesis that the mass function of the accreting satellites determines the inner slope of the DM profile. In comoving coordinates, r, the profile \rho_{dm} \propto 1/(X^\alpha(1+X)^{3-\alpha}), with X=c_\Delta r/r_\Delta, r_\Delta is the virial radius and \alpha =\alpha(M_{dm}), provides a good fit to all the DM halos from dwarf galaxies to clusters at any redshift with the same concentration parameter c_\Delta ~ 7. The slope, \gamma, of the outer parts of the halo appears to depend on the acceleration of the universe: when the scale parameter is a=(1+z)^{-1} < 1, the slope is \gamma ~ 3 as in the NFW profile, but \gamma ~ 4 at a > 1 when \Omega_\Lambda ~ 1 and the universe is inflating.[abridged]Comment: Accepted for publication in MNRAS. 13 pages, including 11 figures and 2 tables. The revised version has an additional discussion section and work on the velocity dispersion anisotrop