Structure Formation With a Long-Range Scalar Dark Matter Interaction

Numerical simulations show that a long-range scalar interaction in a single species of massive dark matter particles causes voids between the concentrations of large galaxies to be more nearly empty, suppresses accretion of intergalactic matter onto galaxies at low redshift, and produces an early generation of dense dark matter halos. These three effects, in moderation, seem to be improvements over the Lambda CDM model predictions for cosmic structure formation. Because the scalar interaction in this model has negligible effect on laboratory physics and the classical cosmological tests, it offers an observationally attractive example of cosmology with complicated physics in the dark sector, notably a large violation of the weak equivalence principle.Comment: 10 pages, 7 figures, revtex4. v2: minor improvements, refs added, version to appear in PR

Galaxy Satellites and the Weak Equivalence Principle

Numerical simulations of the effect of a long-range scalar interaction (LRSI) acting only on nonbaryonic dark matter, with strength comparable to gravity, show patterns of disruption of satellites that can agree with what is seen in the Milky Way. This includes the symmetric Sagittarius stellar stream. The exception presented here to the Kesden and Kamionkowski demonstration that an LRSI tends to produce distinctly asymmetric streams follows if the LRSI is strong enough to separate the stars from the dark matter before tidal disruption of the stellar component, and if stars dominate the mass in the luminous part of the satellite. It requires that the Sgr galaxy now contains little dark matter, which may be consistent with the Sgr stellar velocity dispersion, for in the simulation the dispersion at pericenter exceeds virial. We present other examples of simulations in which a strong LRSI produces satellites with large mass-to-light ratio, as in Draco, or free streams of stars, which might be compared to "orphan" streams.Comment: 14 pages, accepted for publication in PR

Using Perturbative Least Action to Reconstruct Redshift Space Distortions

In this paper, we present a redshift space reconstruction scheme which is analogous to and extends the Perturbative Least Action (PLA) method described by Goldberg & Spergel (2000). We first show that this scheme is effective in reconstructing even nonlinear observations. We then suggest that by varying the cosmology to minimize the quadrupole moment of a reconstructed density field, it may be possible to lower the errorbars on the redshift distortion parameter, $\beta$ as well as to break the degeneracy between the linear bias parameter, $b$, and $\Omega_M$. Finally, we discuss how PLA might be applied to realistic redshift surveys.Comment: 34 Pages LaTeX, including 10 postscript figures. Submitted to Astrophysical Journa

Maximum-Likelihood Comparisons of Tully-Fisher and Redshift Data: Constraints on Omega and Biasing

We compare Tully-Fisher (TF) data for 838 galaxies within cz=3000 km/sec from the Mark III catalog to the peculiar velocity and density fields predicted from the 1.2 Jy IRAS redshift survey. Our goal is to test the relation between the galaxy density and velocity fields predicted by gravitational instability theory and linear biasing, and thereby to estimate $\beta_I = \Omega^{0.6}/b_I,$ where $b_I$ is the linear bias parameter for IRAS galaxies. Adopting the IRAS velocity and density fields as a prior model, we maximize the likelihood of the raw TF observables, taking into account the full range of selection effects and properly treating triple-valued zones in the redshift-distance relation. Extensive tests with realistic simulated galaxy catalogs demonstrate that the method produces unbiased estimates of $\beta_I$ and its error. When we apply the method to the real data, we model the presence of a small but significant velocity quadrupole residual (~3.3% of Hubble flow), which we argue is due to density fluctuations incompletely sampled by IRAS. The method then yields a maximum likelihood estimate $\beta_I=0.49\pm 0.07$ (1-sigma error). We discuss the constraints on $\Omega$ and biasing that follow if we assume a COBE-normalized CDM power spectrum. Our model also yields the 1-D noise noise in the velocity field, including IRAS prediction errors, which we find to be be 125 +/- 20 km/sec.Comment: 53 pages, 20 encapsulated figures, two tables. Submitted to the Astrophysical Journal. Also available at http://astro.stanford.edu/jeff

Einstellungen und Selbstwirksamkeit von Lehrerinnen und Lehrern zur schulischen Inklusion in Deutschland - eine Analyse mit Daten des Nationalen Bildungspanels Deutschlands (NEPS)

In Deutschland wird der gemeinsame Unterricht von Schülerinnen und Schülern mit und ohne sonderpädagogischem Förderbedarf im Schulsystem stark ausgebaut. Als eine wichtige Voraussetzung für eine gelungene Umsetzung des gemeinsamen Unterrichts wird in der Forschung die Einstellungen der beteiligten Lehrerinnen und Lehrer zur Inklusion gesehen. Der vorliegende Bei- trag berichtet über die Selbstwirksamkeit und die allgemeine Einstellung zur Inklusion bei 130 Klassenlehrkräften in der der 2. Welle der Startkohorte 3 (6. Jahrgangsstufe) des Nationalen Bildungspanels (NEPS). Insgesamt haben die Regelschullehrkräfte eine positive Einstellung gegenüber der Inklusion, jedoch ist die Selbstwirksamkeit in Bezug auf Inklusion eher gering ausgeprägt. Die befragten Klassenlehrkräfte in Förderschulen trauen sich dagegen die Umsetzung des gemeinsamen Unterrichts eher zu. Gegenüber der Inklusion haben sie jedoch Bedenken und halten die Förderschule für den optimaleren Förderort für Schülerinnen und Schüler mit sonderpädagogischem Förderbedarf

Reconstruction Analysis of Galaxy Redshift Surveys: A Hybrid Reconstruction Method

In reconstruction analysis of galaxy redshift surveys, one works backwards from the observed galaxy distribution to the primordial density field in the same region, then evolves the primordial fluctuations forward in time with an N-body code. This incorporates assumptions about the cosmological parameters, the properties of primordial fluctuations, and the biasing relation between galaxies and mass. These can be tested by comparing the reconstruction to the observed galaxy distribution, and to peculiar velocity data. This paper presents a hybrid reconstruction method that combines the `Gaussianization'' technique of Weinberg(1992) with the dynamical schemes of Nusser & Dekel(1992) and Gramann(1993). We test the method on N-body simulations and on N-body mock catalogs that mimic the depth and geometry of the Point Source Catalog Redshift Survey and the Optical Redshift Survey. This method is more accurate than Gaussianization or dynamical reconstruction alone. Matching the observed morphology of clustering can limit the bias factor b, independent of Omega. Matching the cluster velocity dispersions and z-space distortions of the correlation function xi(s,mu) constrains the parameter beta=Omega^{0.6}/b. Relative to linear or quasi-linear approximations, a fully non-linear reconstruction makes more accurate predictions of xi(s,mu) for a given beta, thus reducing the systematic biases of beta measurements and offering further scope for breaking the degeneracy between Omega and b. It also circumvents the cosmic variance noise that limits conventional analyses of xi(s,mu). It can also improve the determination of Omega and b from joint analyses of redshift & peculiar velocity surveys as it predicts the fully non-linear peculiar velocity distribution at each point in z-space.Comment: 72 pages including 33 figures, submitted to Ap

Evidence for a Positive Cosmological Constant from Flows of Galaxies and Distant Supernovae

Recent observations of high-redshift supernovae seem to suggest that the global geometry of the Universe may be affected by a `cosmological constant', which acts to accelerate the expansion rate with time. But these data by themselves still permit an open universe of low mass density and no cosmological constant. Here we derive an independent constraint on the lower bound to the mass density, based on deviations of galaxy velocities from a smooth universal expansion. This constraint rules out a low-density open universe with a vanishing cosmological constant, and together the two favour a nearly flat universe in which the contributions from mass density and the cosmological constant are comparable. This type of universe, however, seems to require a degree of fine tuning of the initial conditions that is in apparent conflict with `common wisdom'.Comment: 8 pages, 1 figure. Slightly revised version. Letter to Natur

The end of the Dark Ages in MOND

We study the evolution of a spherically symmetric density perturbation in the Modified Newtonian Dynamics (MOND) model applied to the net acceleration over Hubble flow. The background cosmological model is a $\Lambda$-dominated, low-$\Omega_b$ Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that under these assumptions the first low-mass objects ($M \le 3\times 10^4 M_{\odot}$) may collapse already for $z\sim 30$, which is in quite good agreement with the recent WMAP results. A lower value of $a_0$ would lead to much slower collapse of such objects.Comment: 6 pages, 11 figures, LaTeX 2e with MN2e, MNRAS submitte

Comparison of the ENEAR Peculiar Velocities with the PSCz Gravity Field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky $D_n-\sigma$ catalog and that derived from the galaxy distribution of the IRAS PSCz redshift survey. The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500km/s at 3000km/s. The general flow patterns in the filtered ENEAR and PSCz velocity fields agree well within 6000km/s, assuming a linear biasing relation between the mass and the PSCz galaxies. The comparison allows us to determine the parameter $\beta=\Omega^{0.6}/b$, where $\Omega$ is the cosmological density parameter and $b$ is the linear biasing factor. A likelihood analysis of the ENEAR and PSCz modes yields $\beta=0.5 +- 0.1$, in good agreement with values obtained from Tully-Fisher surveys.Comment: Submitted to MNRA

Observational Constraints on a Variable Dark Energy Model

We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are $\Omega_m = 0.27^{+0.02}_{-0.02}$ (the present matter content) and $w_0=-1.45^{+0.35}_{-0.60}$ (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objectsComment: 10 pages, 12 figures, accepted in PR