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Articles 31 - 44 of 44
Full-Text Articles in Astrophysics and Astronomy
Redshift-Distance Survey Of Early-Type Galaxies: Spectroscopic Data, G. Wegner, M. Bernardi, C. N. A. Willmer, L. N. Da Costa
Redshift-Distance Survey Of Early-Type Galaxies: Spectroscopic Data, G. Wegner, M. Bernardi, C. N. A. Willmer, L. N. Da Costa
Dartmouth Scholarship
We present central velocity dispersions and Mg2 line indices for an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984 had no previous measures. This sample contains the largest set of homogeneous spectroscopic data for a uniform sample of elliptical galaxies in the nearby universe. These galaxies were observed as part of the ENEAR project, designed to study the peculiar motions and internal properties of the local early-type galaxies. Using 523 repeated observations of 317 galaxies obtained during different runs, the data are brought to a common zero point. These multiple observations, taken during the many runs …
Gauge-Invariant Initial Conditions And Early Time Perturbations In Quintessence Universes, Michael Doran, Christian M. Müller, Gregor Schäfer, Christof Wetterich
Gauge-Invariant Initial Conditions And Early Time Perturbations In Quintessence Universes, Michael Doran, Christian M. Müller, Gregor Schäfer, Christof Wetterich
Dartmouth Scholarship
We present a systematic treatment of the initial conditions and evolution of cosmological perturbations in a universe containing photons, baryons, neutrinos, cold dark matter, and a scalar quintessence field. By formulating the evolution in terms of a differential equation involving a matrix acting on a vector comprised of the perturbation variables, we can use the familiar language of eigenvalues and eigenvectors. As the largest eigenvalue of the evolution matrix is fourfold degenerate, it follows that there are four dominant modes with a nondiverging gravitational potential at early times, corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature and neutrino isocurvature …
Effects Of The Sound Speed Of Quintessence On The Microwave Background And Large Scale Structure, Simon Dedeo, R. R. Caldwell, Paul J. Steinhardt
Effects Of The Sound Speed Of Quintessence On The Microwave Background And Large Scale Structure, Simon Dedeo, R. R. Caldwell, Paul J. Steinhardt
Dartmouth Scholarship
We consider how quintessence models in which the sound speed differs from the speed of light and varies with time affect the cosmic microwave background and the fluctuation power spectrum. Significant modifications occur on length scales related to the Hubble radius during epochs in which the sound speed is near zero and the quintessence contributes a non-negligible fraction of the total energy density. For the microwave background, we find that the usual enhancement of the lowest multipole moments by the integrated Sachs-Wolfe effect can be modified, resulting in suppression or bumps instead. Also, the sound speed can produce oscillations and …
Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt
Sensitivity Of The Cosmic Microwave Background Anisotropy To Initial Conditions In Quintessence Cosmology, Rahul Dave, R. R. Caldwell, Paul J. Steinhardt
Dartmouth Scholarship
We analyze the evolution of energy density fluctuations in cosmological scenarios with a mixture of cold dark matter and quintessence, in which the quintessence field is modeled by a constant equation of state. We obtain analytic expressions for the time evolution of the quintessence perturbations in models with light fields. The fluctuations behave analogously to a driven harmonic oscillator, where the driving term arises from the inhomogeneities in the surrounding cosmological fluid. We demonstrate that the homogeneous solution, determined by the initial conditions, is completely subdominant to the inhomogeneous solution for physically realistic scenarios. Thus we show that the cosmic …
Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos
Fine-Tuning Solution For Hybrid Inflation In Dissipative Chaotic Dynamics, Rudnei O. Ramos
Dartmouth Scholarship
We study the presence of chaotic behavior in phase space in the preinflationary stage of hybrid inflation models. This is closely related to the problem of initial conditions associated with these inflationary types of model. We then show how an expected dissipative dynamics of fields just before the onset of inflation can solve or ease considerably the problem of initial conditions, driving the system naturally toward inflation. The chaotic behavior of the corresponding dynamical system is studied by computation of the fractal dimension of the boundary in phase space separating inflationary from noninflationary trajectories. The fractal dimension for this boundary …
Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois
Shortcuts In The Fifth Dimension, Robert Caldwell, David Langlois
Dartmouth Scholarship
If our Universe is a three-brane embedded in a five-dimensional anti-de Sitter spacetime, in which matter is confined to the brane and gravity inhabits an infinite bulk space, then the causal propagation of luminous and gravitational signals is in general different. A gravitational signal traveling between two points on the brane can take a “shortcut” through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitational signal can propagate farther than a luminous signal. We quantify this effect, and analyze the impact …
Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos
Affinity For Scalar Fields To Dissipate, Arjun Berera, Rudnei O. Ramos
Dartmouth Scholarship
The zero-temperature effective equation of motion is derived for a scalar field interacting with other fields. For a broad range of cases, involving interaction with as few as one or two fields, dissipative regimes are found for the scalar field system. The zero-temperature limit constitutes a baseline effect that will be prevalent in any general statistical state. Thus, the results found here provide strong evidence that dissipation is the norm not the exception for an interacting scalar field system. For application to inflationary cosmology, this provides convincing evidence that warm inflation could be a natural dynamics once proper treatment of …
Enear Redshift-Distance Survey: Cosmological Constraints, Stefano Borgani, Mariangela Bernardi, Luiz N. Da Costa, Gary Wegner
Enear Redshift-Distance Survey: Cosmological Constraints, Stefano Borgani, Mariangela Bernardi, Luiz N. Da Costa, Gary Wegner
Dartmouth Scholarship
We present an analysis of the ENEAR sample of peculiar velocities of field and cluster elliptical galaxies, obtained with Dn-σ distances. We use the velocity correlation function ψ1(r) to analyze the statistics of the field object's velocities, while the analysis of the cluster data is based on the estimate of their rms peculiar velocity Vrms. The results are compared with predictions from cosmological models using linear theory. The statistics of the model velocity field is parameterized by the amplitude η8 = σ8Ω and by the shape parameter Γ of the cold dark matter-like power spectrum. …
Gravitational Waves From Collapsing Vacuum Domains, Marcelo Gleiser, Ronald Roberts
Gravitational Waves From Collapsing Vacuum Domains, Marcelo Gleiser, Ronald Roberts
Dartmouth Scholarship
The breaking of an approximate discrete symmetry, the final stages of a first order phase transition, or a postinflationary biased probability distribution for scalar fields are possible cosmological scenarios characterized by the presence of unstable domain wall networks. Combining analytical and numerical techniques, we show that the nonspherical collapse of these domains can be a powerful source of gravitational waves. We compute their contribution to the stochastic background of gravitational radiation and explore their observability by present and future gravitational wave detectors.
The Motions Of Clusters Of Galaxies And The Dipoles Of The Peculiar Velocity Field, Riccardo Giovanelli, Martha P. Haynes, John J. Salzer, Gary Wegner
The Motions Of Clusters Of Galaxies And The Dipoles Of The Peculiar Velocity Field, Riccardo Giovanelli, Martha P. Haynes, John J. Salzer, Gary Wegner
Dartmouth Scholarship
In preceding papers of this series, TF relations for galaxies in 24 clusters with radial velocities between 1000 and 9200 km s-1 (SCI sample) were obtained, a Tully-Fisher (TF) template relation was constructed, and mean offsets of each cluster with respect to the template were 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 km s-1 and that their distribution has a line-of-sight dispersion of 300 km s-1, suggesting …
Flows On Scales Of 150 Mpc?, K. R. Müller, W. Freudling, R. Watkins, G. Wegner
Flows On Scales Of 150 Mpc?, K. R. Müller, W. Freudling, R. Watkins, G. Wegner
Dartmouth Scholarship
In order to investigate the reality of large-scale streaming motion on scales of up to 150 Mpc, we have studied the peculiar motions of ~200 early-type galaxies in three directions of the South Equatorial Strip at distances out to ~20,000 km s-1. The new Automatic Plate Measuring Facility South Equatorial Strip Catalog (-175<δ<+25) was used to select the sample of field galaxies in three directions: (1) 15h10m-16h10m; (2) 20h30m-21h50m; (3) 00h10m-01h30m. New R-band CCD photometry and spectroscopic data for the galaxies are used. The fundamental plane distance-indicator …
Peculiar Velocity Dipoles Of Field Galaxies, Riccardo Giovanelli, Martha P. Haynes, Wolfram Freudling, Luiz N. Da Costa, John J. Salzer, Gary Wegner
Peculiar Velocity Dipoles Of Field Galaxies, Riccardo Giovanelli, Martha P. Haynes, Wolfram Freudling, Luiz N. Da Costa, John J. Salzer, Gary Wegner
Dartmouth Scholarship
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 Mass Distribution In The Nearby Universe, Luiz N. Da Costa, Wolfram Freudling, Gary Wegner, Riccardo Giovanelli
The Mass Distribution In The Nearby Universe, Luiz N. Da Costa, Wolfram Freudling, Gary Wegner, Riccardo Giovanelli
Dartmouth Scholarship
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 …
A Test Of The Lauer-Postman Bulk Flow, Riccardo Giovanelli, Martha P. Haynes, Gary Wegner, Luiz N. Da Costa
A Test Of The Lauer-Postman Bulk Flow, Riccardo Giovanelli, Martha P. Haynes, Gary Wegner, Luiz N. Da Costa
Dartmouth Scholarship
We use Tully-Fisher distances for a sample of field late spiral galaxies to test the Lauer & Postman result suggestive of a bulk flow with respect to the cosmic microwave background reference frame, of amplitude of +689 km s-1 in the direction l = 343°, b = +52°. A total of 432 galaxies are used, subdivided between two cones, of 30° semiaperture each and pointed toward the apex and antapex of the LP motion, respectively. The peculiar velocities in the two data sets are inconsistent with a bulk flow of the amplitude claimed by Lauer & Postman. When combined …