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

Wide Angle Redshift Distortions Revisited

We explore linear redshift distortions in wide angle surveys from the point of view of symmetries. We show that the redshift space two-point correlation function can be expanded into tripolar spherical harmonics of zero total angular momentum $S_{l_1 l_2 l_3}(\hat x_1, \hat x_2, \hat x)$. The coefficients of the expansion $B_{l_1 l_2 l_3}$ are analogous to the $C_l$'s of the angular power spectrum, and express the anisotropy of the redshift space correlation function. Moreover, only a handful of $B_{l_1 l_2 l_3}$ are non-zero: the resulting formulae reveal a hidden simplicity comparable to distant observer limit. The $B_{l_1 l_2 l_3}$ depend on spherical Bessel moments of the power spectrum and $f = \Omega^{0.6}/b$. In the plane parallel limit, the results of \cite{Kaiser1987} and \cite{Hamilton1993} are recovered. The general formalism is used to derive useful new expressions. We present a particularly simple trigonometric polynomial expansion, which is arguably the most compact expression of wide angle redshift distortions. These formulae are suitable to inversion due to the orthogonality of the basis functions. An alternative Legendre polynomial expansion was obtained as well. This can be shown to be equivalent to the results of \cite{SzalayEtal1998}. The simplicity of the underlying theory will admit similar calculations for higher order statistics as well.Comment: 6 pages, 1 figure, ApJL submitte

Accurate radial velocity and metallicity of the Large Magellanic Cloud old globular clusters NGC1928 and NGC1939

We present results obtained from spectroscopic observations of red giants located in the fields of the Large Magellanic Cloud (LMC) globular clusters (GCs) NGC1928 and NGC1939. We used the GMOS and AAOmega+2dF spectrographs to obtain spectra centred on the Ca II triplet, from which we derived individual radial velocities (RVs) and metallicities. From cluster members we derived mean RVs of RVNGC1928 = 249.58±4.65 km s-1 and RVNGC1939 = 258.85±2.08 km s-1, and mean metallicities of [Fe/H]NGC1928 = -1.30±0.15 dex and [Fe/H]NGC1939 = -2.00±0.15 dex. We found that both GCs have RVs and positions consistent with being part of the LMC disc, so that we rule out any possible origin, but in the same galaxy. By computing the best solution of a disc that fully contains each GC, we obtained circular velocities for the 15 known LMC GCs. We found that 11/15 of the GCs share the LMC rotation derived from HST and Gaia DR2 proper motions. This outcome reveals that the LMC disc existed since the very early epoch of the galaxy formation and experienced the steep relatively fast chemical enrichment shown by its GC metallicities. The four remaining GCs turned out to have circular velocities not compatible with an in situ cluster formation, but rather with being stripped from the SMC.Fil: Piatti, Andres Eduardo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hwang, N.. Korea Astronomy And Space Science Institute; Corea del SurFil: Cole, A. A.. University of Tasmania; AustraliaFil: Angelo, M. S.. Laboratorio Nacional de Astrofisica; BrasilFil: Emptage, B.. University of Tasmania; Australi

An Evaluation of Physical Activity Levels amongst University Employees

Approximately 60% of the world’s population do not meet the physical activity (PA) guidelines. Physical inactivity is increasing in occupations, with work-related health issues becoming more prevalent. University employees’ work in a range of job roles and PA levels in this population is unclear. Thus, this study aimed to evaluate PA levels amongst university employees in a UK Higher Education institution. Four hundred employees (male = 131, female = 269) partook in this quantitative study and completed an online International Physical Activity Questionnaire Long Form (IPAQ-LF) to assess total moderate to vigorous PA (MVPA) and work-related MVPA. A Mann-Whitney U test examined differences in total MVPA and work-related MVPA between genders and a Kruskal-Wallis H test examined differences in total MVPA and work related MVPA between job roles. The findings showed that university employees engaged in a median of 330 minutes and 1770 METs of MVPA across all domains of IPAQ-LF. Further, the median time spent in total work PA was 30 minutes and 123 METs. There was a significant difference between genders, as males engaged in 150 minutes more total MVPA compared to females (p 0.05). Findings suggest that job role does not affect PA levels within university workplace, although they do propose that males engage in more MVPA compared to females. As a result of the subjective nature of this research, objective research is required to confirm current findings

Beyond capitalism and liberal democracy: on the relevance of GDH Cole’s sociological critique and alternative

This article argues for a return to the social thought of the often ignored early 20th-century English thinker GDH Cole. The authors contend that Cole combined a sociological critique of capitalism and liberal democracy with a well-developed alternative in his work on guild socialism bearing particular relevance to advanced capitalist societies. Both of these, with their focus on the limitations on ‘free communal service’ in associations and the inability of capitalism to yield emancipation in either production or consumption, are relevant to social theorists looking to understand, critique and contribute to the subversion of neoliberalism. Therefore, the authors suggest that Cole’s associational sociology, and the invitation it provides to think of formations beyond capitalism and liberal democracy, is a timely and valuable resource which should be returned to

Observation of non-Markovian micro-mechanical Brownian motion

All physical systems are to some extent open and interacting with their environment. This insight, basic as it may seem, gives rise to the necessity of protecting quantum systems from decoherence in quantum technologies and is at the heart of the emergence of classical properties in quantum physics. The precise decoherence mechanisms, however, are often unknown for a given system. In this work, we make use of an opto-mechanical resonator to obtain key information about spectral densities of its condensed-matter heat bath. In sharp contrast to what is commonly assumed in high-temperature quantum Brownian motion describing the dynamics of the mechanical degree of freedom, based on a statistical analysis of the emitted light, it is shown that this spectral density is highly non-Ohmic, reflected by non-Markovian dynamics, which we quantify. We conclude by elaborating on further applications of opto-mechanical systems in open system identification.Comment: 5+6 pages, 3 figures. Replaced by final versio

Optical vector network analysis of ultra-narrow transitions in 166^{166}Er3+^{3+}:7^7LiYF4_4

We present optical vector network analysis (OVNA) of an isotopically purified $^{166}$Er$^{3+}$:$^7$LiYF$_4$ crystal. The OVNA method is based on generation and detection of modulated optical sideband by using a radio-frequency vector network analyzer. This technique is widely used in the field of microwave photonics for the characterization of optical responses of optical devices such as filters and high-Q resonators. However, dense solid-state atomic ensembles induce a large phase shift on one of the optical sidebands which results in the appearance of extra features on the measured transmission response. We present a simple theoretical model which accurately describes the observed spectra and helps to reconstruct the absorption profile of a solid-state atomic ensemble as well as corresponding change of the refractive index in the vicinity of atomic resonances.Comment: 4 pages, 5 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

An Inversion Method for Measuring Beta in Large Redshift Surveys

A precision method for determining the value of Beta= Omega_m^{0.6}/b, where b is the galaxy bias parameter, is presented. In contrast to other existing techniques that focus on estimating this quantity by measuring distortions in the redshift space galaxy-galaxy correlation function or power spectrum, this method removes the distortions by reconstructing the real space density field and determining the value of Beta that results in a symmetric signal. To remove the distortions, the method modifies the amplitudes of a Fourier plane-wave expansion of the survey data parameterized by Beta. This technique is not dependent on the small-angle/plane-parallel approximation and can make full use of large redshift survey data. It has been tested using simulations with four different cosmologies and returns the value of Beta to +/- 0.031, over a factor of two improvement over existing techniques.Comment: 16 pages including 6 figures Submitted to The Astrophysical Journa

The Bispectrum as a Signature of Gravitational Instability in Redshift-Space

The bispectrum provides a characteristic signature of gravitational instability that can be used to probe the Gaussianity of the initial conditions and the bias of the galaxy distribution. We study how this signature is affected by redshift distortions using perturbation theory and high-resolution numerical simulations. We obtain perturbative results for the multipole expansion of the redshift-space bispectrum which provide a natural way to break the degeneracy between bias and $\Omega$ present in measurements of the redshift-space power spectrum. We propose a phenomenological model that incorporates the perturbative results and also describes the bispectrum in the transition to the non-linear regime. We stress the importance of non-linear effects and show that inaccurate treatment of these can lead to significant discrepancies in the determination of bias from galaxy redshift surveys. At small scales we find that the bispectrum monopole exhibits a strong configuration dependence that reflects the velocity dispersion of clusters. Therefore, the hierarchical model for the three-point function does not hold in redshift-space.Comment: 19 pages, 4 figures. Revised version accepted for publication in Ap