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San Jose State University

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Articles 151 - 180 of 221

Full-Text Articles in Astrophysics and Astronomy

Diffusive Transport Enhanced By Thermal Velocity Fluctuations, Alejandro Garcia, A. Donev, A. De La Fuente, J. B. Bell Jan 2011

Diffusive Transport Enhanced By Thermal Velocity Fluctuations, Alejandro Garcia, A. Donev, A. De La Fuente, J. B. Bell

Faculty Publications

We study the contribution of advection by thermal velocity fluctuations to the effective diffusion coefficient in a mixture of two identical fluids. We find good agreement between a simple fluctuating hydrodynamics theory and particle and finite-volume simulations. The enhancement of the diffusive transport depends on the system size L and grows as ln⁡(L/L0) in quasi-two-dimensional systems, while in three dimensions it scales as L0-1-L-1, where L0 is a reference length. Our results demonstrate that fluctuations play an important role in the hydrodynamics of small-scale systems.

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Proximity Of The Superconducting Dome And The Quantum Critical Point In The Two-Dimensional Hubbard Model, S. Yang, H. Fotso, S.-Q. Su, D. Galanakis, Ehsan Khatami, J.-H. She, J. Moreno, J. Zaanen, M. Jarrell Jan 2011

Proximity Of The Superconducting Dome And The Quantum Critical Point In The Two-Dimensional Hubbard Model, S. Yang, H. Fotso, S.-Q. Su, D. Galanakis, Ehsan Khatami, J.-H. She, J. Moreno, J. Zaanen, M. Jarrell

Faculty Publications

We use the dynamical cluster approximation to understand the proximity of the superconducting dome to the quantum critical point in the two-dimensional Hubbard model. In a BCS formalism, Tc may be enhanced through an increase in the d-wave pairing interaction (Vd) or the bare pairing susceptibility (χ0d). At optimal doping, where Vd is revealed to be featureless, we find a power-law behavior of χ0d(ω=0), replacing the BCS log, and strongly enhanced Tc. We suggest experiments to verify our predictions.

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Galaxies In Cdm With Halo Abundance Matching: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, Velocity Function, And Clustering, S. Trujillo-Gomez, A. Klypin, J. Primack, Aaron J. Romanowsky Jan 2011

Galaxies In Cdm With Halo Abundance Matching: Luminosity-Velocity Relation, Baryonic Mass-Velocity Relation, Velocity Function, And Clustering, S. Trujillo-Gomez, A. Klypin, J. Primack, Aaron J. Romanowsky

Faculty Publications

It has long been regarded as difficult if not impossible for a cosmological model to account simultaneously for the galaxy luminosity, mass, and velocity distributions. We revisit this issue using a modern compilation of observational data along with the best available large-scale cosmological simulation of dark matter (DM). We find that the standard cosmological model, used in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits—at least on average—all basic statistics of galaxies with circular velocities V circ > 80 km s–1 calculated at a radius of ~10 kpc. Our primary observational constraint is the luminosity-velocity (LV) relation—which generalizes …

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Wide-Field Precision Kinematics Of The M87 Globular Cluster System, J. Strader, Aaron J. Romanowsky, J. P. Brodie, L. R. Spitler, M. A. Beasley, Jacob A. Arnold, N. Tamura, R. M. Sharples, N. Arimoto Jan 2011

Wide-Field Precision Kinematics Of The M87 Globular Cluster System, J. Strader, Aaron J. Romanowsky, J. P. Brodie, L. R. Spitler, M. A. Beasley, Jacob A. Arnold, N. Tamura, R. M. Sharples, N. Arimoto

Faculty Publications

We present the most extensive combined photometric and spectroscopic study to date of the enormous globular cluster (GC) system around M87, the central giant elliptical galaxy in the nearby Virgo Cluster. Using observations from DEIMOS and the Low Resolution Imaging Spectrometer at Keck, and Hectospec on the Multiple Mirror Telescope, we derive new, precise radial velocities for 451 GCs around M87, with projected radii from ~5 to 185 kpc. We combine these measurements with literature data for a total sample of 737 objects, which we use for a re-examination of the kinematics of the GC system of M87. The velocities …

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The Fossil Record Of Two-Phase Galaxy Assembly: Kinematics And Metallicities In The Nearest S0 Galaxy, J, A, Arnold, Aaron J. Romanowsky, J. P. Brodie, L. Chomiuk, L. R. Spitler, J. Strader, A. J. Benson, D. A. Forbes Jan 2011

The Fossil Record Of Two-Phase Galaxy Assembly: Kinematics And Metallicities In The Nearest S0 Galaxy, J, A, Arnold, Aaron J. Romanowsky, J. P. Brodie, L. Chomiuk, L. R. Spitler, J. Strader, A. J. Benson, D. A. Forbes

Faculty Publications

We present a global analysis of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging from Suprime-Cam on the Subaru telescope, and multi-slit spectra of the field stars and globular clusters (GCs) obtained using Keck-DEIMOS/LRIS and Magellan-IMACS. Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly (v/σ gsim 1.5). At larger radii, the rotation declines dramatically to v/σ ~ 0.7, but remains well aligned with the inner regions. The radial decrease in characteristic metallicity of both …

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Star Clusters In M31: Old Clusters With Bar Kinematics, H. Morrison, N. Caldwell, R. P. Schiavon, E. Athanassoula, Aaron J. Romanowsky, P. Harding Jan 2011

Star Clusters In M31: Old Clusters With Bar Kinematics, H. Morrison, N. Caldwell, R. P. Schiavon, E. Athanassoula, Aaron J. Romanowsky, P. Harding

Faculty Publications

We analyze our accurate kinematical data for the old clusters in the inner regions of M31. These velocities are based on high signal-to-noise Hectospec data. The data are well suited for analysis of M31's inner regions because we took particular care to correct for contamination by unresolved field stars from the disk and bulge in the fibers. The metal-poor clusters show kinematics that are compatible with a pressure-supported spheroid. The kinematics of metal-rich clusters, however, argue for a disk population. In particular the innermost region (inside 2 kpc) shows the kinematics of the x 2 family of bar periodic orbits, …

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Evidence For Two Phases Of Galaxy Formation From Radial Trends In The Globular Cluster System Of Ngc 1407, D. A. Forbes, L. R. Spitler, J. Strader, Aaron J. Romanowsky, J. P. Brodie, C. Foster Jan 2011

Evidence For Two Phases Of Galaxy Formation From Radial Trends In The Globular Cluster System Of Ngc 1407, D. A. Forbes, L. R. Spitler, J. Strader, Aaron J. Romanowsky, J. P. Brodie, C. Foster

Faculty Publications

Here we present the colours of individual globular clusters (GCs) around the massive elliptical galaxy NGC 1407 out to a projected galactocentric radius of 140 kpc or 17 galaxy effective radii (Re). Such data are a proxy for the halo metallicity. We find steep, and similar, metallicity gradients of ∼−0.4 dex dex−1 for both the blue (metal poor) and red (metal rich) GC subpopulations within 5–8.5 Re (40–70 kpc). At larger radii the mean GC colours (metallicity) are constant. A similar behaviour is seen in a wide-field study of M87's GC system, and in our own Galaxy. We interpret these …

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The Dark Halo Of He Hydra I Galaxy Cluster: Core, Cusp, Cosmological? Dynamics Of Ngc 3311 And Its Globular Cluster System, T. Richtler, R. Salinas, I. Misgeld, M. Hilker, G.K. T. Hau, Aaron J. Romanowsky, Y. Schuberth, M. Spolaor Jan 2011

The Dark Halo Of He Hydra I Galaxy Cluster: Core, Cusp, Cosmological? Dynamics Of Ngc 3311 And Its Globular Cluster System, T. Richtler, R. Salinas, I. Misgeld, M. Hilker, G.K. T. Hau, Aaron J. Romanowsky, Y. Schuberth, M. Spolaor

Faculty Publications

Context. Some galaxy clusters exhibit shallow or even cored dark matter density profiles in their central regions rather than the predicted steep or cuspy profiles, conflicting with the standard understanding of dark matter. NGC 3311 is the central cD galaxy of the Hydra I cluster (Abell 1060). Aims. We use globular clusters around NGC 3311, combined with kinematical data of the galaxy itself, to investigate the dark matter distribution in the central region of Hydra I. Methods. Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask spectroscopy, are used to calculate velocity dispersions which are well defined out …

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Quantum Criticality Due To Incipient Phase Separation In The Two-Dimensional Hubbard Model, Ehsan Khatami, K. Mikelsons, D. Galanakis, A. Macridin, J. Moreno, R. Scalettar, M. Jarrell May 2010

Quantum Criticality Due To Incipient Phase Separation In The Two-Dimensional Hubbard Model, Ehsan Khatami, K. Mikelsons, D. Galanakis, A. Macridin, J. Moreno, R. Scalettar, M. Jarrell

Faculty Publications

We investigate the two-dimensional Hubbard model with next-nearest-neighbor hopping, t′, using the dynamical cluster approximation. We confirm the existence of a first-order phase-separation transition terminating at a second-order critical point at filling nc(t′) and temperature Tps(t′). We find that as t′ approaches zero, Tps(t′) vanishes and nc(t′) approaches the filling associated with the quantum critical point separating the Fermi liquid from the pseudogap phase. We propose that the quantum critical point under the superconducting dome is the zero-temperature limit of the line of second-order critical points.

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Cluster Solver For Dynamical Mean-Field Theory With Linear Scaling In Inverse Temperature, Ehsan Khatami, C. Lee, Z. Bai, R. Scalettar, M. Jarrell May 2010

Cluster Solver For Dynamical Mean-Field Theory With Linear Scaling In Inverse Temperature, Ehsan Khatami, C. Lee, Z. Bai, R. Scalettar, M. Jarrell

Faculty Publications

Dynamical mean-field theory and its cluster extensions provide a very useful approach for examining phase transitions in model Hamiltonians and, in combination with electronic structure theory, constitute powerful methods to treat strongly correlated materials. The key advantage to the technique is that, unlike competing real-space methods, the sign problem is well controlled in the Hirsch-Fye (HF) quantum Monte Carlo used as an exact cluster solver. However, an important computational bottleneck remains; the HF method scales as the cube of the inverse temperature, β. This often makes simulations at low temperatures extremely challenging. We present here a method based on determinant …

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A Hybrid Particle-Continuum Method For Hydrodynamics Of Complex Fluids, Alejandro Garcia, A. Donev, J. B. Bell, B. Alder Jan 2010

A Hybrid Particle-Continuum Method For Hydrodynamics Of Complex Fluids, Alejandro Garcia, A. Donev, J. B. Bell, B. Alder

Faculty Publications

A previously developed hybrid particle-continuum method [J. B. Bell, A. Garcia, and S. A. Williams, Multiscale Model. Simul., 6 (2008), pp. 1256–1280] is generalized to dense fluids and two- and three-dimensional flows. The scheme couples an explicit fluctuating compressible Navier–Stokes solver with the isotropic direct simulation Monte Carlo (DSMC) particle method [A. Donev, A. L. Garcia, and B. J. Alder, J. Stat. Mech. Theory Exp., 2009 (2009), article P11008]. To achieve bidirectional dynamic coupling between the particle (microscale) and continuum (macroscale) regions, the continuum solver provides state-based boundary conditions to the particle subdomain, while the particle solver provides flux-based boundary …

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The Globular Cluster System Of Ngc 1399. V. Dynamics Of The Cluster System Out To 80 Kpc, Y. Schuberth, T. Richtler, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky, L. Infante Jan 2010

The Globular Cluster System Of Ngc 1399. V. Dynamics Of The Cluster System Out To 80 Kpc, Y. Schuberth, T. Richtler, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky, L. Infante

Faculty Publications

Globular clusters (GCs) are tracers of the gravitational potential of their host galaxies. Moreover, their kinematic properties may provide clues for understanding the formation of GC systems and their host galaxies. We use the largest set of GC velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations (Richtler et al. 2004) of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies. The GC velocities are used to study the kinematics, their relation with population properties, and the dark matter halo of NGC 1399. We have obtained 477 …

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Central Dark Matter Content Of Early-Type Galaxies: Scaling Relations And Connections With Star Formation Histories, N. R. Napolitano, Aaron J. Romanowsky, A. J. Tortora Jan 2010

Central Dark Matter Content Of Early-Type Galaxies: Scaling Relations And Connections With Star Formation Histories, N. R. Napolitano, Aaron J. Romanowsky, A. J. Tortora

Faculty Publications

We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of 〈ρDM〉∝R−2eff provides the first clear indication of cuspy DM haloes in these galaxies – akin to standard Λ cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as …

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Computational Fluctuating Fluid Dynamics, Alejandro Garcia, J. B. Bell, S. Williams Jan 2010

Computational Fluctuating Fluid Dynamics, Alejandro Garcia, J. B. Bell, S. Williams

Faculty Publications

This paper describes the extension of a recently developed numerical solver for the Landau-Lifshitz Navier-Stokes (LLNS) equations to binary mixtures in three dimensions. The LLNS equations incorporate thermal fluctuations into macroscopic hydrodynamics by using white-noise fluxes. These stochastic PDEs are more complicated in three dimensions due to the tensorial form of the correlations for the stochastic fluxes and in mixtures due to couplings of energy and concentration fluxes (e.g., Soret effect). We present various numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate good agreement with theoretical results and molecular simulation

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Validity Of The Spin-Susceptibility “Glue” Approximation For Pairing In The Two-Dimensional Hubbard Model, Ehsan Khatami, A. Macridin, M. Jarrell Nov 2009

Validity Of The Spin-Susceptibility “Glue” Approximation For Pairing In The Two-Dimensional Hubbard Model, Ehsan Khatami, A. Macridin, M. Jarrell

Faculty Publications

We examine the validity of the weak-coupling spin-susceptibility “glue” approximation (SSGA) in a two-dimensional Hubbard model for cuprates. For comparison, we employ the well-established dynamical cluster approximation (DCA) with a quantum Monte Carlo algorithm as a cluster solver. We compare the leading eigenvalues and corresponding eigenfunctions of the DCA and SSGA pairing matrices. For realistic model parameters, we find that the SSGA fails to capture the leading pairing symmetries seen in the DCA. Furthermore, when the SSGA is improved through the addition of a term with d-wave symmetry, the strength of this additional term is found to be larger than …

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Thermodynamics Of The Quantum Critical Point At Finite Doping In The Two-Dimensional Hubbard Model Studied Via The Dynamical Cluster Approximation, K. Mikelsons, Ehsan Khatami, D. Galanakis, A. Macridin, J. Moreno, M. Jarrell Oct 2009

Thermodynamics Of The Quantum Critical Point At Finite Doping In The Two-Dimensional Hubbard Model Studied Via The Dynamical Cluster Approximation, K. Mikelsons, Ehsan Khatami, D. Galanakis, A. Macridin, J. Moreno, M. Jarrell

Faculty Publications

We study the thermodynamics of the two-dimensional Hubbard model within the dynamical cluster approximation. We use continuous time quantum Monte Carlo as a cluster solver to avoid the systematic error which complicates the calculation of the entropy and potential energy (double occupancy). We find that at a critical filling, there is a pronounced peak in the entropy divided by temperature, S/T, and in the normalized double occupancy as a function of doping. At this filling, we find that specific heat divided by temperature, C/T, increases strongly with decreasing temperature and kinetic and potential energies vary like T2 ln T. These …

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Mapping The Dark Side With Deimos: Globular Clusters, X-Ray Gas, And Dark Matter In The Ngc 1407 Group, Aaron J. Romanowsky, J. Strader, L. Spitler, R. Johnson, J. P. Brodie, D. A. Forbes, T. Ponman May 2009

Mapping The Dark Side With Deimos: Globular Clusters, X-Ray Gas, And Dark Matter In The Ngc 1407 Group, Aaron J. Romanowsky, J. Strader, L. Spitler, R. Johnson, J. P. Brodie, D. A. Forbes, T. Ponman

Faculty Publications

NGC 1407 is the central elliptical in a nearby evolved group of galaxies apparently destined to become a galaxy cluster core. We use the kinematics of globular clusters (GCs) to probe the dynamics and mass profile of the group's center, out to a radius of 60 kpc (~10 galaxy effective radii)—the most extended data set to date around an early-type galaxy. This sample consists of 172 GC line-of-sight velocities, most of them newly obtained using Keck/DEIMOS, with a few additional objects identified as dwarf-globular transition objects or as intragroup GCs. We find weak rotation for the outer parts of the …

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Dearth Of Dark Matter Or Massive Dark Halo? Mass-Shape-Anisotropy Degeneracies Revealed By Nmagic Dynamical Models Of The Elliptical Galaxy Ngc 3379, F. De Lorenzi, O. Gerhard, L. Coccato, M. Arnaboldi, M. Capaccioli, K. C. Freeman, K. Kuijken, M. R. Merrifield, N. R. Napolitano, E. Noordermeer, Aaron J. Romanowsky, V. P. Debattista Jan 2009

Dearth Of Dark Matter Or Massive Dark Halo? Mass-Shape-Anisotropy Degeneracies Revealed By Nmagic Dynamical Models Of The Elliptical Galaxy Ngc 3379, F. De Lorenzi, O. Gerhard, L. Coccato, M. Arnaboldi, M. Capaccioli, K. C. Freeman, K. Kuijken, M. R. Merrifield, N. R. Napolitano, E. Noordermeer, Aaron J. Romanowsky, V. P. Debattista

Faculty Publications

Recent results from the Planetary Nebula Spectrograph (PNS) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter (DM) halo expected in Λ cold dark matter (ΛCDM) cosmology. We present a detailed dynamical study of this galaxy, combining ground based long-slit spectroscopy, integral-field data from the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) instrument and PNS data reaching to more than seven effective radii. We construct dynamical models with the flexible χ2-made-to-measure (χ2M2M) particle method implemented in the NMAGIC …

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Kinematic Properties Of Early-Type Galaxy Haloes Using Planetary Nebulae, L. Coccato, O. Gerhard, M. Arnaboldi, P. Das, N. G. Douglas, K. Kuijken, M. R. Merrifield, N. R. Napolitano, Aaron J. Romanowsky, E. Noordermeer, M. Capaccioli, A. Cortesi, F. De Lorenzi, K. C. Freeman Jan 2009

Kinematic Properties Of Early-Type Galaxy Haloes Using Planetary Nebulae, L. Coccato, O. Gerhard, M. Arnaboldi, P. Das, N. G. Douglas, K. Kuijken, M. R. Merrifield, N. R. Napolitano, Aaron J. Romanowsky, E. Noordermeer, M. Capaccioli, A. Cortesi, F. De Lorenzi, K. C. Freeman

Faculty Publications

We present new planetary nebulae (PNe) positions, radial velocities and magnitudes for six early-type galaxies obtained with the Planetary Nebulae Spectrograph (PNS), along with derived two-dimensional velocity and velocity dispersion fields, and the α parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for three galaxies in the sample, obtained with the FOcal Reducer and low dispersion Spectrograph (FORS2) at the Very Large Telescope (VLT). We extend this study to include additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, including previous PNS studies, in order to obtain …

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Central Mass-To-Light Ratios And Dark Matter Fractions In Early-Type Galaxies, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, G. Covone Jan 2009

Central Mass-To-Light Ratios And Dark Matter Fractions In Early-Type Galaxies, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, G. Covone

Faculty Publications

Dynamical studies of local elliptical galaxies and the Fundamental Plane point to a strong dependence of the total mass-to-light ratio (M/L) on luminosity with a relation of the form M/L∝Lγ. The ‘tilt’γ may be caused by various factors, including stellar population properties (metallicity, age and star formation history), initial mass function, rotational support, luminosity profile non-homology and dark matter (DM) fraction. We evaluate the impact of all these factors using a large uniform data set of local early-type galaxies from Prugniel & Simien. We take particular care in estimating the stellar masses, using a general star formation history, and comparing …

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The Planetary Nebula Spectrograph Elliptical Galaxy Survey: The Dark Matter In Ngc 4494, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, M. Capaccioli, N. G. Douglas, E. Noordermeer, O. Gerhard, M. Arnaboldi, F. De Lorenzi, K. Kuijken, M. R. Merrifield, E. O'Sullivan, A. Cortesi, P. Das, K. C. Freeman Jan 2009

The Planetary Nebula Spectrograph Elliptical Galaxy Survey: The Dark Matter In Ngc 4494, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, M. Capaccioli, N. G. Douglas, E. Noordermeer, O. Gerhard, M. Arnaboldi, F. De Lorenzi, K. Kuijken, M. R. Merrifield, E. O'Sullivan, A. Cortesi, P. Das, K. C. Freeman

Faculty Publications

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside 1Re. The velocity dispersion profile declines with radius, though not very steeply, down to ∼70 km s−1 at the last data point. We …

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Probing The 2d Kinematic Structure Of Early-Type Galaxies Out To 3 Effective Radii, R. N. Proctor, D. A. Forbes, J. P. Brodie, Aaron J. Romanowsky, J. Strader, M. Spolaor, J. T. Mendel, L. Spitler Jan 2009

Probing The 2d Kinematic Structure Of Early-Type Galaxies Out To 3 Effective Radii, R. N. Proctor, D. A. Forbes, J. P. Brodie, Aaron J. Romanowsky, J. Strader, M. Spolaor, J. T. Mendel, L. Spitler

Faculty Publications

We detail an innovative new technique for measuring the two-dimensional (2D) velocity moments (rotation velocity, velocity dispersion and Gauss–Hermite coefficients h3 and h4) of the stellar populations of galaxy haloes using spectra from Keck DEIMOS (Deep Imaging Multi-Object Spectrograph) multi-object spectroscopic observations. The data are used to reconstruct 2D rotation velocity maps. Here we present data for five nearby early-type galaxies to ∼three effective radii. We provide significant insights into the global kinematic structure of these galaxies, and challenge the accepted morphological classification in several cases. We show that between one and three effective radii the velocity dispersion declines very …

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Effect Of Long-Range Hopping On Tc In A Two-Dimensional Hubbard-Holstein Model Of The Cuprates, Ehsan Khatami, A. Macridin, M. Jarrell Aug 2008

Effect Of Long-Range Hopping On Tc In A Two-Dimensional Hubbard-Holstein Model Of The Cuprates, Ehsan Khatami, A. Macridin, M. Jarrell

Faculty Publications

We study the effect of long-range hoppings on Tc for the two-dimensional (2D) Hubbard model with and without Holstein phonons using parameters evaluated from band-structure calculations for cuprates. Employing the dynamical cluster approximation (DCA) with a quantum Monte Carlo (QMC) cluster solver for a 4-site cluster, we observe that without phonons, the long-range hoppings, t′ and t′′, generally suppress Tc. We argue that this trend remains valid for larger clusters. In the presence of the Holstein phonons, a finite t′ enhances Tc in the under-doped region for the hole-doped system, consistent with local-density approximation (LDA) calculations and experiment. This is …

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The Dark Matter Halo Of Ngc 1399- Cdm Or Mond?, T. Richtler, Y. Schuberth, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky Jan 2008

The Dark Matter Halo Of Ngc 1399- Cdm Or Mond?, T. Richtler, Y. Schuberth, M. Hilker, B. Dirsch, L. Bassino, Aaron J. Romanowsky

Faculty Publications

Context. Central galaxies in galaxy clusters may be key discriminants in the competition between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND). Aims. We investigate the dark halo of NGC 1399, the central galaxy of the Fornax cluster, out to a galactocentric distance of 80 kpc. Methods.The data base consists of 656 radial velocities of globular clusters obtained with MXU/VLT and GMOS/Gemini, which is the largest sample so far for any galaxy. We performed a Jeans analysis for a non-rotating isotropic model. Results.An NFW halo with the parameters $r_{\rm s} = 50\,\rm {kpc}$ and $\varrho_{\rm s} = …

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Testing The Nature Of S0 Galaxies Using Planetary Nebula Kinematics In Ngc 1023, E. Noordermeer, M. R. Merrifield, L. Coccato, M. Arnaboldi, M. Capaccioli, N. G. Douglas, K. C. Freeman, O. Gerhard, K. Kuijken, F. De Lorenzi, N. R. Napolitano, Aaron J. Romanowsky Jan 2008

Testing The Nature Of S0 Galaxies Using Planetary Nebula Kinematics In Ngc 1023, E. Noordermeer, M. R. Merrifield, L. Coccato, M. Arnaboldi, M. Capaccioli, N. G. Douglas, K. C. Freeman, O. Gerhard, K. Kuijken, F. De Lorenzi, N. R. Napolitano, Aaron J. Romanowsky

Faculty Publications

We investigate the manner in which lenticular galaxies are formed by studying their stellar kinematics: an S0 formed from a fading spiral galaxy should display similar cold outer disc kinematics to its progenitor, while an S0 formed in a minor merger should be more dominated by random motions. In a pilot study, an attempt to distinguish between these scenarios, we have measured the planetary nebula (PN) kinematics of the nearby S0 system NGC 1023. Using the Planetary Nebula Spectrograph, we have detected and measured the line-of-sight velocities of 204 candidate planetary nebulae (PNe) in the field of this galaxy. Out …

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Stochastic Hard-Sphere Dynamics For Hydrodynamics Of Non-Ideal Fluids, Alejandro Garcia, A. Donev, B. J. Alder Jan 2008

Stochastic Hard-Sphere Dynamics For Hydrodynamics Of Non-Ideal Fluids, Alejandro Garcia, A. Donev, B. J. Alder

Faculty Publications

A novel stochastic fluid model is proposed with a nonideal structure factor consistent with compressibility, and adjustable transport coefficients. This stochastic hard sphere dynamics (SHSD) algorithm is a modification of the direct simulation Monte Carlo algorithm and has several computational advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD results in an equation of state and a pair correlation function identical to that of a deterministic Hamiltonian system of penetrable spheres interacting with linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD fluid is verified for the Brownian motion of a nanoparticle suspended in a compressible solvent.

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Algorithm Refinement For Fluctuating Hydrodynamics, Alejandro Garcia, S. Williams, J. B. Bell Jan 2007

Algorithm Refinement For Fluctuating Hydrodynamics, Alejandro Garcia, S. Williams, J. B. Bell

Faculty Publications

This paper introduces an adaptive mesh and algorithm refinement method for fluctuating hydrodynamics. This particle-continuum hybrid simulates the dynamics of a compressible fluid with thermal fluctuations. The particle algorithm is direct simulation Monte Carlo (DSMC), a molecular-level scheme based on the Boltzmann equation. The continuum algorithm is based on the Landau–Lifshitz Navier–Stokes (LLNS) equations, which incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. It uses a recently developed solver for the LLNS equations based on third-order Runge–Kutta. We present numerical tests of systems in and out of equilibrium, including time-dependent systems, and demonstrate dynamic adaptive refinement by the …

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The Star Pile In Abell 545, R. Salinas, T. Richtler, M. J. West, Aaron J. Romanowsky, Y. Schuberth Jan 2007

The Star Pile In Abell 545, R. Salinas, T. Richtler, M. J. West, Aaron J. Romanowsky, Y. Schuberth

Faculty Publications

Context.Struble (1988, ApJ, 330, L25) found what appeared to be a cD halo without cD galaxy in the center of the galaxy cluster Abell 545. This remarkable feature has been passed almost unnoticed for nearly twenty years. Aims.Our goal is to review Struble's claim by providing a first (preliminary) photometric and spectroscopic analysis of this "star pile". Methods.Based on archival VLT-images and long-slit spectra obtained with Gemini-GMOS, we describe the photometric structure and measure the redshift of the star pile and of the central galaxy. Results.The star pile is indeed associated with Abell 545. Its velocity is higher by about …

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Numerical Methods For The Stochastic Landau-Lifshitz Navier-Stokes Equations, Alejandro Garcia, J. B. Bell, S. Williams Jan 2007

Numerical Methods For The Stochastic Landau-Lifshitz Navier-Stokes Equations, Alejandro Garcia, J. B. Bell, S. Williams

Faculty Publications

The Landau-Lifshitz Navier-Stokes (LLNS) equations incorporate thermal fluctuations into macroscopic hydrodynamics by using stochastic fluxes. This paper examines explicit Eulerian discretizations of the full LLNS equations. Several computational fluid dynamics approaches are considered (including MacCormack’s two-step Lax-Wendroff scheme and the piecewise parabolic method) and are found to give good results for the variance of momentum fluctuations. However, neither of these schemes accurately reproduces the fluctuations in energy or density. We introduce a conservative centered scheme with a third-order Runge-Kutta temporal integrator that does accurately produce fluctuations in density, energy, and momentum. A variety of numerical tests, including the random walk …

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The Pn.S Elliptical Galaxy Survey: Data Reduction, Planetary Nebula Catalog, And Basic Dynamics For Ngc 3379, N. G. Douglas, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, K. Kuijken, M. R. Merrifield, M. Arnaboldi, O. Gerhard, K. C. Freeman, H. R. Merrett, E. Noordermeer, M. Capaccioli Jan 2007

The Pn.S Elliptical Galaxy Survey: Data Reduction, Planetary Nebula Catalog, And Basic Dynamics For Ngc 3379, N. G. Douglas, N. R. Napolitano, Aaron J. Romanowsky, L. Coccato, K. Kuijken, M. R. Merrifield, M. Arnaboldi, O. Gerhard, K. C. Freeman, H. R. Merrett, E. Noordermeer, M. Capaccioli

Faculty Publications

We present results from Planetary Nebula Spectrograph (PN.S) observations of the elliptical galaxy NGC 3379 and a description of the data reduction pipeline. We detected 214 planetary nebulae, of which 191 are ascribed to NGC 3379 and 23 to the companion galaxy NGC 3384. Comparison with data from the literature shows that the PN.S velocities have an internal error of lesssim20 km s-1 and a possible offset of similar magnitude. We present the results of kinematic modeling and show that the PN kinematics is consistent with absorption-line data in the region where they overlap. The resulting combined kinematic data set, …

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