Session B14 - Galaxies, Supernovae, and Cosmology.
ORAL session, Saturday morning, April 28
Room 14, Renaissance Hotel$

[B14.001] Galaxies in a Charged Universe

A model of galactic structure is formulated in which the visible regions of a galaxy are embedded in a larger region of charged matter. The dark matter problem is addressed in this context. Galactic structure is shown to be stable only for a extremely large universe and a nearly constant charge to density ratio.

[B14.002] Black Hole Formation by Rossby Vortices

The central galactic black hole, BH, mass is predicted from the collapse of an initial Lyman-\alpha cloud. Damped Lyman-\alpha clouds are the first large scale, (R_Lyman_\alpha \simeq 300 kpc, M_Lyman_\alpha \simeq 10^11 M_ødot, and \Sigma_Baryonic \simeq 10^-4 g cm^-2) structures. The rotation velocity of the combined dark and baryonic matter compared to that required for Keplerian support is small, \lambda \simeq .07. The baryonic matter collapses homologously by shocks and cooling with conserved angular momentum. Upon reaching a radius of partial Keplerian support where the Mclauren spheroid instability, \lambda_spheroid \simeq 0.4 is initiated then tidal torquing produces the "flat rotation curve" (FRC). This occurs when R_spheroid/R_cloud \simeq (\lambda_cloud/ \lambda_spheroid)^2 , and where the mass thickness \Sigma_spheroid \simeq \Sigma_Lyman_\alpha (R_spheroid/R_cloud)^2 \simeq \Sigma_Lyman-\alpha (\lambda_cloud/ \lambda_spheroid)^4 \simeq 0.1 g cm^-2. The interior baryonic mass following the FRC condition then becomes M_flat = M_spheroid (R/R_spheroid) and \Sigma_flat = \Sigma_spheroid (R_spheroid/R). Thus as the FRC forms, the mass thickness increases as \propto 1/R. At a critical thickness \Sigma_Rossby \simeq 100 g cm^-2, the Rossby vortex instability forms because of the confinement of heat. All of the mass of the resulting accretion disk collapses to a BH where M_BH = M_spheroid (\Sigma_spheroid/\Sigma_Rossby) = M_Lyman_\alpha (\lambda_cloud/ \lambda_spheroid)^4 (\Sigma_Lyman_\alpha/ \Sigma_Rossby) \simeq 10^8 M_ødot.

[B14.003] Massive Black-Hole Binaries in Galactic Nuclei

We present N-body simulations of the formation and the evolution of massive black-hole binaries in galactic nuclei. We simulate the merger of two spherical galaxies containing central point masses and \rho\sim r^-2 central density cusps. Once the two black holes form a bound pair at the center of the merged galaxies, the evolution is continued using the direct summation code NBODY6 at high resolution. Immediately following the formation of a black-hole binary, the merged density cusp is nearly homologous to the cusps in the initial galaxies. However the central density decreases rapidly as the binary ejects stars which pass near to it, reducing the slope of the cusp from \sim r^-2 to \sim r^-1. The binary exhibits Brownian motion about the center while engaging in hard encounters with stars on radial orbits that are ejected at high speed. Ejection induces further shrinking of the binary at a lower but approximately constant rate. We discuss the dynamics of the binaries in the limit of large N, appropriate to real galactic nuclei, and discuss the possibility that massive black-hole binaries exist in the nuclei of some galaxies.

[B14.004] Dynamical Rotational Instability at Low T/|W|

Dynamical instability is shown to occur in differentially rotating polytropes with N = 3.33 and T/|W| >= 0.14. This instability has a strong m=1 global mode, although the m=2, 3, and 4 modes also appear. Such instability may allow a centrifugally-hung core to begin collapsing to neutron star densities on a dynamical timescale. If it occurs in a supermassive star, it may produce gravitational radiation detectable by LISA.

[B14.005] Consequences of Accretion onto Primordial Compact Objects

Many lines of evidence suggest that nonbaryonic dark matter constitutes roughly 30 percent of the critical closure density, but the composition of this dark matter is unknown. One class of candidates for the dark matter is stellar-mass compact objects formed in the early universe. Specific candidates of this type include black holes formed at the epoch of the QCD phase transition, quark stars, and boson stars. We explore the effects of accretion onto these objects, and show that the resulting radiation may have significant effects on ionization (and hence on the observed CMB power spectrum) and on early structure formation. Observations of radiation from high redshifts can therefore be used to constrain the contribution of primordial compact objects to dark matter.

[B14.006] Connecting Numerical Models of Galaxy Collisions to Multi-Wavelength Observations

Numerical simulations involving only basic physics are a powerful tool for understanding complex systems. We have performed a detailed study of the colliding galaxy system Arp 119 by comparing observations with a 3D computer simulation employing gravity and hydrodynamics. Morphological and velocity information yield a likely orientation for the system. Comparing the model at various times with observations taken at multiple wavelengths reveals the history of the large-scale, collision-induced star formation that occurred in the disk galaxy. We find that the star formation followed the passage of a single gas density wave through the disk, and that the star formation did not occur continuously, but only during discrete periods. Spatially, the star formation took place over long, continuous arcs and in a string of distinct knots. We present a summary of the types of physical information we have obtained through comparisons of observations and simulations, and we describe applications of these results to the evolution of galaxies.

[B14.007] Galaxies Associated with Damped Lyman Alpha Absorbers at z=4

We report the results of a search for "Lyman break" galaxies in fields containing z=4 Damped Lyman alpha absorbers (DLAs) along the line of sight to distant quasars. We searched for emission from galaxies physically associated with the DLAs, which are dense clouds of neutral hydrogen believed to be the building blocks of normal galaxies. We have conducted a survey to find all z>3.5 galaxies in the field in order to explore the clustering environment of the DLAs. In essence we have applied large-scale structure techniques to the study of galaxy formation by exploring the cross-correlation between bright star-forming (Lyman break) galaxies and dense clouds of neutral gas (DLAs) in the early universe. Our initial results (Gawiser et al 2001) find an overdensity of galaxies near a DLA at z=3.86, implying that DLAs are highly biased and hence quite massive. If the cross-correlation is equally strong in other DLAs, this would represent a serious challenge to the prevailing hierarchical models of cosmological structure formation.

[B14.008] Three-dimensional modeling of Type Ia supernova explosions

The paper presents first results of modeling a deflagration explosion in a non-rotating, Chandrasekhar-mass carbon-oxygen (CO) white dwarf. Simulations show that the turbulent flame speed grows exponentially, reaches approximately 30% of the speed of sound, and then declines as the large-scale turbulence is frozen by expansion. The freezing of turbulent motions appears to be a crucial physical mechanism regulating the strength of a deflagration explosion in SNIa. The energy of the explosion is comparable to that of a typical SNIa. However, the presence of the outer layer of unburned CO and the formation of intermediate mass elements and pockets of unburned CO near the center pose problems for SNIa spectra. Sensitivity of the explosion outcome to initial conditions and its relation to a diversity of SNIa is discussed.

[B14.009] Questions and Implications of an Accelerating Universe Inferred from Type Ia Supernovae Observations.

Measurements of distance to Type Ia supernovae have been interpreted as evidence for an accelerating expansion of the Universe. There is, however, no known compatible theoretical framework to account for this effect. Proposed mechanisms include introduction of a new type of matter (``dark energy" or ``quintessence") or invocation of Einstein's cosmological constant which, in modern terms, corresponds to vacuum energy associated with quantum fluctuations. Yet there are no experimental observations to support the existence of such matter or energy associated with our Universe. The goal of the present work is to examine whether the conclusion that the Universe is accelerating is conclusive. Evidence for an accelerating expansion is based on measurements of the redshift and luminosity of supernovae billions of light years away. These measurements depend on the velocity of light which itself depends on the medium of propagation. Hence it is critical to analyze the properties of the medium; of relevance are the mean matter density, the critical density, the Hubble time and the deceleration parameter. Our analysis focuses on the fact that these quantities are not constant in time but rather change as the Universe expands. The results and conclusion of our investigation will be discussed.

[B14.010] Strong lensing of supernovae

We discuss the possibility of strong lensing of high-redshift supernovae. We examine how likely it is for such an event to occur. Furthermore, we explore what science can be done given such an event. In addition to improving measures of the Hubble constant, a multiply-imaged type Ia supernovae will break the mass-sheet degeneracy, and allow for a precise measurement of the intervening mass.

[B14.011] Zodiacal Infrared Variability and Influences on Cosmological Information

The Diffuse Infrared Background Experiment (DIRBE) flew on the Cosmic Background Explorer (COBE) in 1989--90 and executed a full--sky survey in 10 bands from 1.2 to 240 \mum. The DIRBE data were used to construct a model of the signal from the interplanetary dust cloud so that it could be removed from the data as a first step in determining the faint IR signal from the cosmic infrared background (CIRB). An analysis of the results after removing the model disclosed that the Zodiacal IR signal is variable and is correlated with solar variations. The variations show wavelength--dependent periodicities, have amplitudes at levels of the estimated CIRB for most of the bands, and are spatially nonuniform. The nature of this discovery and its consequences in determining the CIRB will be discussed.

[B14.012] CMB observations with MAXIMA and MAXIPOL

We discuss the status of the MAXIMA and MAXIPOL cosmic microwave background balloon-borne experiments. The MAXIMA and MAXIPOL instruments consist of a 1.3 m off-axis Gregorian telescope and a receiver housing a 16 element array of 100 mK bolometers. Observations are made in 3 frequency bands centered on 150, 240, and 410 GHz. We recently released temperature anisotropy power spectrum results (l=36 to l=785) from the August 1998 MAXIMA-1 flight. During the second MAXIMA flight, launched in June 1999 (MAXIMA-2), we scanned 225 square degrees of CMB sky with extremely low galactic dust contamination. Approximately 50 square degrees of this region overlaps the MAXIMA-1 observations. MAXIMA-2 data analysis is currently in progress. MAXIPOL will attempt detection of the CMB polarization anisotropy. The instrument is based on the MAXIMA receiver which has the highest sensitivity of any CMB receiver to date. Instrument preparation is in progress and a 36 hour flight is planned for 2001.

MAXIMA is supported by NASA though grants NAG5-4454 and NAG5-3941, and by the Center for Particle Astrophyiscs, a National Science and Technology Center operated by the University of California, Berkeley, under Cooperative Agreement No. AST 9120005. MAXIPOL is supported by NASA through grants NAG5-9349 and NAG5-9398.

[B14.013] Results from the First Two Observing Seasons of PIQUE

We report on the first two seasons of the Princeton IQU Experiment (PIQUE). PIQUE is a ground-based telescope designed to measure the polarization of the Cosmic Microwave Background (CMB). During the first season (1/19/00-4/2/00), PIQUE measured the Q Stokes parameter on a ring at declination of 89 degrees from the roof of the Physics Department at Princeton University using a 90 GHz correlation polarimeter with a full-width-half maximum beam of 0.24 degrees. PIQUE's observations from the first season yielded a new limit on the polarization of the CMB in the multipole range 100<\ell<600. During the second season (currently in progress), PIQUE will measure the U Stokes parameter in the same ring using a combination of the 90 GHz polarimeter and a new 40 GHz polarimeter. Preliminary results from these observations will be presented.

[B14.014] Measuring the Mass of the Universe with SDSS Weak Lensing

Inhomogeneities in the distribution of mass in the Universe are revealed by the distortions they create in the images of distant galaxies. Measurements of this gravitational lensing allow detection of mass where no luminous test masses exist and in regions which are not in dynamical equilibrium. We measure the lensing masses of more than 40,000 galaxies observed by the Sloan Digital Sky Survey. All lens galaxies have spectroscopically determined redshifts and highly accurate CCD photometry. Galaxy masses are determined on halo scales, out to radii of 250 h^-1 kpc. We determine scaling relations between mass and luminosity in the five SDSS passbands, from u^\prime to z^\prime. By combining these mass-to-light scaling relations with SDSS measurements of the galaxy luminosity function, we place strong constraints on the cosmic density of mass associated with galaxies.

Part B of program listing