Testing the Peculiar Velocity Field predicted from Redshift Surveys

The reconstruction of the peculiar velocity field from the 1.936~Jy iras selected sample of galaxies is compared to a similar reconstruction from an optically selected sample. A general method for combining different samples to reconstruct a self-consistent density and peculiar velocity field is presented. The method is applied to determine how sensitive the derived peculiar velocity field is to the characteristics of the sample used. The possibility that the iras galaxies do not trace the general galaxy population is explored adopting a simple model of linear biasing between the iras and optical samples. We find that the velocity fields derived from the two samples are consistent, within the estimated shot noise error, for the case of no relative bias. This result suggests that the predicted peculiar velocity field based on iras samples is not sensitive to the sampling properties of iras galaxies. Combined with previous suggestion of a relative biasing of iras galaxies on small scales (about 5 h^-1Mpc), this result suggests scale dependent biasing.Comment: tar-compressed and uudecoded postscript files, 12 pages+8 figure

SIMP (Strongly Interacting Massive Particle) Search

We consider laboratory experiments that can detect stable, neutral strongly interacting massive particles (SIMPs). We explore the SIMP annihilation cross section from its minimum value (restricted by cosmological bounds) to the barn range, and vary the mass values from a GeV to a TeV. We also consider the prospects and problems of detecting such particles at the Tevatron.Comment: Latex. 7 pages, 1 eps figure. Proceedings to the 4th UCLA Symposium on Dark Matter DM2000, Marina del Rey, CA, USA, Feb. 23-25, 200

Determination of Malmquist Bias and Selection Effects from Monte Carlo Simulations

Maps of the peculiar velocity field derived from distance relations are affected by Malmquist type bias and selection effects. Because of the large number of interdependent effects, they are in most cases difficult to treat analytically. Monte Carlo simulations are used to understand and evaluate these effects. In these simulations the true spatial distribution and relevant properties of galaxies as well as selection effects and observational uncertainties are realistically modeled. The results of the simulation can be directly applied to correct observed peculiar velocity maps. The simulation is used to investigate biases in samples of measured peculiar velocities by Lynden-Bell et al. (ApJ, 326, 19, 1988). Willick (ApJ, 351, L5, 1990) and the new sample of spiral galaxies by Haynes et al. (BAAS, 25, 1403, 1993). Based on the results obtained from the application of our method to toy models we find that the method is a useful tool to estimate the bias induced both by inhomogeneities and selection effects. This is a crucial step for the analysis of the Haynes et al. sample which was selected with a redshift dependent criterion

The Mass Distribution in the Nearby Universe

We present a new reconstruction of the mass density and the peculiar velocity fields in the nearby universe using recent measurements of Tully-Fisher distances for a sample of late spirals. We find significant differences between our reconstructed fields and those obtained in earlier work: overdensities tend to be more compact while underdense regions, consisting of individual voids, are more abundant. Our results suggest that voids observed in redshift surveys of galaxies represent real voids in the underlying matter distribution. While we detect a bulk velocity of ~300 km s-1, within a top-hat window 6000 km s-1 in radius, the flow is less coherent than previously claimed, exhibiting a bifurcation toward the Perseus-Pisces and the Great Attractor complexes. This is the first time that this feature is seen from peculiar velocity measurements. The observed velocity field resembles, more closely than any previous reconstruction, the velocity field predicted from self-consistent reconstructions based on all-sky redshift surveys. This better match is likely to affect estimates of the parameter β = Ω0.6/b and its uncertainty based on velocity-velocity comparisons

The Tully-Fisher Relation and H0

The use of the Tully-Fisher (TF) relation for the determination of H0 relies on the availability of an adequate template TF relation and of reliable primary distances. Here we use a TF template relation with the best available kinematical zero point, obtained from a sample of 24 clusters of galaxies extending to cz ~ 9000 km s-1, and the most recent set of Cepheid distances for galaxies fit for TF use. The combination of these two ingredients yields H0 = 69 ± 5 km s-1 Mpc-1. The approach is significantly more accurate than the more common application with single cluster (e.g., Virgo, Coma) samples

The Motions of Clusters of Galaxies and the Dipoles of the Peculiar Velocity Field

In preceding papers of this series, TF relations for galaxies in 24 clusters with radial velocities between 1000 and 9200 km/s (SCI sample) were obtained, a Tully-Fisher (TF) template relation was constructed and mean offsets of each cluster with respect to the template obtained. Here, an estimate of the line-of-sight peculiar velocities of the clusters and their associated errors are given. It is found that cluster peculiar velocities in the Cosmic Microwave Background reference frame do not exceed 600 k/ms and that their distribution has a line-of-sight dispersion of 300 k/ms, suggesting a more quiescent cluster peculiar velocity field than previously reported. When measured in a reference frame in which the Local Group is at rest, the set of clusters at cz > 3000 km/s exhibits a dipole moment in agreement with that of the CMB, both in amplitude and apex direction. It is estimated that the bulk flow of a sphere of 6000 km/s radius in the CMB reference frame is between 140 and 320 km/s. These results are in agreement with those obtained from an independent sample of field galaxies (Giovanelli et al. 1998; see astro-ph/9807274)Comment: 9 pages, 2 tables, 7 figures, uses AAS LaTex; to appear in A

Peculiar Velocity Dipoles of Field Galaxies

The Tully-Fisher (TF) relation is applied to obtain peculiar velocities of field spiral galaxies and to calculate dipoles of the peculiar velocity field to cz8000 km s-1. The field galaxy sample is spatially coextensive with and completely independent of a cluster sample, for which dipole characteristics are given in a separate paper. Dipoles of the peculiar velocity field are obtained separately by applying (1) an inverse version of the TF relation and selecting galaxies by redshift windowing and (2) a direct TF relation, with velocities corrected for the inhomogeneous Malmquist bias and windowing galaxies by TF distance. The two determinations agree, as they do with the cluster sample. When measured in a reference frame in which the Local Group is at rest, the dipole moment of field galaxies farther than ~4000 km s-1 is in substantial agreement, both in amplitude and direction, with that exhibited by the cosmic microwave background radiation field

Peculiar Velocities of Clusters in Cold Dark Matter Models

Recently, peculiar velocity measurements became available for a new sample of galaxy clusters, hereafter the SCI sample. From an accurately calibrated Tully-Fisher relation for spiral galaxies, we compute the rms peculiar velocity, Vrms, and compare it with the linear theory predictions of COBE-normalized low-density and open cold dark matter models (ΛCDM and OCDM, respectively). Confidence levels for model rejection are estimated using a Monte Carlo procedure in order to generate a large ensemble of artificial data sets for each model. Following Zaroubi et al., we express our results in terms of constraints on the (Ω0, npr, h) parameter space. Such constraints turn into σ8Ω00.6 = 0.50−0.14+0.25 at the 90% confidence level, thus in agreement with results from cluster abundance. We show that our constraints are also consistent with those implied by the shape of the galaxy power spectrum within a rather wide range for the values of the model parameters. Finally, we point out that our findings disagree at about the 3 σ level with respect to those by Zaroubi et al., based on the Mark III catalog, which tend to prefer larger Ω0 values within the CDM class of models

The I-Band Tully-Fisher Relation for Sc Galaxies: 21 Centimeter H I Line Data

A compilation of 21 cm line spectral parameters specifically designed for application of the Tully-Fisher (TF) distance method is presented for 1201 spiral galaxies, primarily field Sc galaxies, for which optical I-band photometric imaging is also available. New H I line spectra have been obtained for 881 galaxies. For an additional 320 galaxies, spectra available in a digital archive have been reexamined to allow application of a single algorithm for the derivation of the TF velocity width parameter. A velocity width algorithm is used that provides a robust measurement of rotational velocity and permits an estimate of the error on that width taking into account the effects of instrumental broadening and signal-to-noise. The digital data are used to establish regression relations between measurements of velocity widths using other common prescriptions so that comparable widths can be derived through conversion of values published in the literature. The uniform H I line widths presented here provide the rotational velocity measurement to be used in deriving peculiar velocities via the TF method