Astrophysics and Astronomy Commons^™

Phantom Energy: Dark Energy With W < − 1 Causes A Cosmic Doomsday, Robert R. Caldwell, Marc Kamionkowski, Nevin N. Weinberg

Dartmouth Scholarship

We explore the consequences that follow if the dark energy is phantom energy, in which the sum of the pressure and energy density is negative. The positive phantom-energy density becomes infinite in finite time, overcoming all other forms of matter, such that the gravitational repulsion rapidly brings our brief epoch of cosmic structure to a close. The phantom energy rips apart the Milky Way, solar system, Earth, and ultimately the molecules, atoms, nuclei, and nucleons of which we are composed, before the death of the Universe in a “big rip.”

Redshift-Distance Survey Of Early-Type Galaxies: Circular-Aperture Photometry, M. V. Alonso, M. Bernardi, L. N. Da Costa, G. Wegner

Dartmouth Scholarship

We present R -band CCD photometry for 1332 early-type galaxies, observed as part of the ENEAR survey of peculiar motions using early-type galaxies in the nearby universe. Circular apertures are used to trace the surface brightness profiles, which are then fitted by a two-component bulge-disk model. From the fits, we obtain the structural parameters required to estimate galaxy distances using the Dn - and fundamental plane relations. We find that about 12% of the galaxies are well represented by a pure r1/4 law, while 87% are best fitted by a two-component model. There are 356 repeated observations of 257 galaxies …

A Limit On The Cosmological Mass Density And Power Spectrum From The Rotation Curves Of Low Surface Brightness Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

The concentrations of the cuspy dark matter halos predicted by simulations of cold dark matter are related to the cosmology in which the halos form. Observational constraints on halo concentration therefore map into constraints on cosmological parameters. In order to explain the observed concentrations of dark matter-dominated low surface brightness galaxies, we require a cosmology with rather little power on galaxy scales. Formally, we require σ 8Γ0.6 < 0.23, where Γ0.6 is a modified shape parameter appropriate to this problem. Practically, this means that either Ωm < 0.2 or σ8 < 0.8. These limits apply as long as we insist that the cuspy halos found in simulations must describe the halos of low surface brightness galaxies. A low-density cosmology helps with the low observed concentrations, but it offers no explanation of the many cases where the shape of the density profile deviates from the predicted cuspy form. These cases must have suffered very extensive mass redistribution if the current halo formation picture is not to fail outright. It is far from clear whether any of the mass redistribution mechanisms that have been suggested (e.g., feedback) are viable.

Observational Constraints On General Relativistic Energy Conditions, Cosmic Matter Density And Dark Energy From X-Ray Clusters Of Galaxies And Type-La Supernovae, P. Schuecker, R. R. Caldwell, H. Böhringer, C. A. Collins

Dartmouth Scholarship

New observational constraints on the cosmic matter density Ωm and an effectively redshift-independent equation

of state parameter wx of the dark energy are obtained while simultaneously testing the strong and null energy conditions of

general relativity on macroscopic scales. The combination of REFLEX X-ray cluster and type-Ia supernova data shows that

for a flat Universe the strong energy condition might presently be violated whereas the null energy condition seems to be

fulfilled. This provides another observational argument for the present accelerated cosmic expansion and the absence of exotic

physical phenomena related to a broken null energy condition. The marginalization of …

Redshift-Distance Survey Of Early-Type Galaxies. I. The Enearc Cluster Sample*, M. Bernardi, M. V. Alonso, L. N. Da Costa, C. N. A. Willmer, A. Wegner

Dartmouth Scholarship

This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D-n-sigma template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg-2, and the angular diameter d(n)), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to …

The Afterglow And Complex Environment Of The Optically Dim Burst Grb 980613, Jens Hjorth, Bjarne Thomsen, Svend R. Nielsen, Michael I. Andersen, Stephen T. Holland, Johan U. Fynbo, Holger Pederson, Andreas O. Jaunsen, Jules P. Halpern, Robert Fesen, Javier Gorosabel, Alberto Castro-Tirado, Richard G. Mcmahon, Michael D. Hoenig, Gunnlaugur Bjornsson, Lorenzo Amati, Nial R. Tanvir, Priyamvada Natarajan

Dartmouth Scholarship

We report the identification of the optical afterglow of GRB 980613 in R- and I-band images obtained between 16 and 48 hr after the gamma-ray burst. Early near-infrared (NIR) H and K' observations are also reported. The afterglow was optically faint (R ≈ 23) at discovery but did not exhibit an unusually rapid decay (power-law decay slope α < 1.8 at 2 σ). The optical/NIR spectral index (β_RH < 1.1) was consistent with the optical-to-X-ray spectral index (β_RX ≈ 0.6), indicating a maximal reddening of the afterglow of ≈0.45 mag in R. Hence, the dimness of the optical afterglow was mainly due to the fairly flat spectral shape rather than internal reddening …

Comparing The Sfi Peculiar Velocities With The Pscz Gravity Field: A Velmod Analysis, E. Branchini, W. Freudling, L. N. Da Costa, C. S. Frenk, R. Giovanelli, M. P. Haynes, J. J. Salzer, G. Wegner, I. Zehavi

Dartmouth Scholarship

We compare the peculiar velocities derived from the I-band Tully–Fisher (TF) relation for 989 field spiral galaxies in the SFI catalogue with the predicted velocity field derived from the IRAS PSCz galaxy redshift survey. We assume linear gravitational instability theory and apply the maximum likelihood technique, VELMOD to SFI galaxies within a redshift cz LG =6000 km s⁻¹. The resulting calibration of the TF relation is consistent with a previous, independent calibration for a similar sample of spirals residing in clusters. Our analysis provides an accurate estimate of the quantity β_I ≡ Ω_m^{0.6 …}

Large-Scale Power Spectrum And Structures From The Enear Galaxy Peculiar Velocity Catalogue, S. Zaroubi, M. Bernardi, L. N. Da Costa, Y. Hoffman, M. V. Alonso, G. Wegner

Dartmouth Scholarship

We estimate the mass density fluctuations power spectrum (PS) on large scales by applying a maximum likelihood technique to the peculiar velocity data of the recently completed redshift—distance survey of early-type galaxies (hereafter ENEAR). Parametric cold dark matter (CDM)-like models for the PS are assumed, and the best-fitting parameters are determined by maximizing the probability of the model given the measured peculiar velocities of the galaxies, their distances and estimated errors. The method has been applied to CDM models with and without COBE normalization. The general results are in agreement with the high-amplitude power spectra found from similar analyses of …

Comparison Of The Enear Peculiar Velocities With The Pscz Gravity Field, A Nusser, L. N. Da Costa, E Branchini, M. Bernardi, M V. Alonso, G Wegner

Dartmouth Scholarship

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky Dn−σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSCz). 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 1500kms⁻¹ at 3000kms⁻¹. The general flow patterns in the filtered ENEAR and PSCz velocity fields agree well within 6000kms⁻¹, assuming a linear biasing relation between the mass and …

A Desktop Universe For The Introductory Astronomy Laboratory, Laurence A. Marschall, Glenn A. Snyder, Paul Richard Cooper

Physics and Astronomy Faculty Publications

What is a well-intentioned astronomy instructor to do? There is no argument that experience with the real world is desirable in any astronomy course, especially the introductory classes that fulfill the science distribution requirements at many colleges and universities. Though it is a simple matter to take students out of doors, show them the motions of the Sun, Moon, and stars, and have them squint for a few seconds at Saturn's rings through a telescope, these activities represent only a small portion of the subject matter of modern astronomy. It is simply not possible, given the constraints of time, weather, …

The Warps Survey - Iv. The X-Ray Luminosity-Temperature Relation Of High-Redshift Galaxy Clusters, B. W. Fairley, L. R. Jones, C. Scharf, H. Ebeling, E. Perlman, D. Horner, G. Wegner, M. Malkan

Dartmouth Scholarship

We present a measurement of the cluster X-ray luminosity-temperature (L-T) relation out to high redshift (z∼0.8). Combined ROSAT PSPC spectra of 91 galaxy clusters detected in the Wide Angle ROSAT Pointed Survey (WARPS) are simultaneously fitted in redshift and luminosity bins. The resulting temperature and luminosity measurements of these bins, which occupy a region of the high-redshift L-T relation not previously sampled, are compared with existing measurements at low redshift in order to constrain the evolution of the L-T relation. We find the best fit to low-redshift (z<0.2) cluster data, at T …