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Faculty Publications

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Articles 361 - 390 of 685

Full-Text Articles in Astrophysics and Astronomy

All-Sky Search For Periodic Gravitational Waves In The Full S5 Ligo Data, J. Abadie, B. P. Abbott, R. Abbott, T. D. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt, P. Ajith, B. Allen, G. S. Allen, E. Amador Ceron, D. Amariutei, R. S. Amin, S. B. Anderson, W. G. Anderson, K. Arai, M. A. Arain, M. C. Araya, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, B. E. Aylott, S. Babak, P. Baker, G. Ballardin, S. Ballmer, Tiffany Z. Summerscales Jan 2012

All-Sky Search For Periodic Gravitational Waves In The Full S5 Ligo Data, J. Abadie, B. P. Abbott, R. Abbott, T. D. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt, P. Ajith, B. Allen, G. S. Allen, E. Amador Ceron, D. Amariutei, R. S. Amin, S. B. Anderson, W. G. Anderson, K. Arai, M. A. Arain, M. C. Araya, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, B. E. Aylott, S. Babak, P. Baker, G. Ballardin, S. Ballmer, Tiffany Z. Summerscales

Faculty Publications

We report on an all-sky search for periodic gravitational waves in the frequency band 50-800Hz and with the frequency time derivative in the range of 0 through -6×10-9Hz/s. Such a signal could be produced by a nearby spinning and slightly nonaxisymmetric isolated neutron star in our Galaxy. After recent improvements in the search program that yielded a 10× increase in computational efficiency, we have searched in two years of data collected during LIGO's fifth science run and have obtained the most sensitive all-sky upper limits on gravitational-wave strain to date. Near 150Hz our upper limit on worst-case linearly polarized strain …

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Testing Yukawa-Like Potentials From F(R)-Gravity In Elliptical Galaxies, N. R. Napolitano, S. Capozziello, Aaron J. Romanowsky, M. Capaccioli, C. Tortora Jan 2012

Testing Yukawa-Like Potentials From F(R)-Gravity In Elliptical Galaxies, N. R. Napolitano, S. Capozziello, Aaron J. Romanowsky, M. Capaccioli, C. Tortora

Faculty Publications

We present the first analysis of extended stellar kinematics of elliptical galaxies where a Yukawa-like correction to the Newtonian gravitational potential derived from f(R)-gravity is considered as an alternative to dark matter. In this framework, we model long-slit data and planetary nebula data out to 7 R eff of three galaxies with either decreasing or flat dispersion profiles. We use the corrected Newtonian potential in a dispersion-kurtosis Jeans analysis to account for the mass-anisotropy degeneracy. We find that these modified potentials are able to fit nicely all three elliptical galaxies and the anisotropy distribution is consistent with that estimated if …

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Evidence For Inhomogeneous Reionization In The Local Universe From Metal-Poor Globular Cluster Systems, L. R. Spitler, Aaron J. Romanowsky, J. Diemand, J. Strader, D. A. Forbes, B. Moore, J. P. Brodie Jan 2012

Evidence For Inhomogeneous Reionization In The Local Universe From Metal-Poor Globular Cluster Systems, L. R. Spitler, Aaron J. Romanowsky, J. Diemand, J. Strader, D. A. Forbes, B. Moore, J. P. Brodie

Faculty Publications

Exploiting a fundamental characteristic of galaxy assembly in the Λ cold dark matter paradigm, the observed spatial biasing and kinematics of metal-poor globular star clusters are used to constrain the local reionization epoch around individual galaxies. Selecting three galaxies located in different environments, the first attempt at constraining the environmental propagation of reionization in the local Universe is carried out. The joint constraint from the three galaxies (Graphic) agrees remarkably well with the latest Wilkinson Microwave Anisotropy Probe constraint on zreion for a simple instantaneous reionization model. More importantly, the range of zreion values found here is consistent with the …

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The Sluggs Survey: Ngc 3115, A Critical Test Case For Metallicity Bimodality In Globular Cluster Systems, J. P. Brodie, C. Usher, C. Conroy, J. Strader, J. A. Arnold, D. A. Forbes, Aaron J. Romanowsky Jan 2012

The Sluggs Survey: Ngc 3115, A Critical Test Case For Metallicity Bimodality In Globular Cluster Systems, J. P. Brodie, C. Usher, C. Conroy, J. Strader, J. A. Arnold, D. A. Forbes, Aaron J. Romanowsky

Faculty Publications

Due to its proximity (9 Mpc) and the strongly bimodal color distribution of its spectroscopically well-sampled globular cluster (GC) system, the early-type galaxy NGC 3115 provides one of the best available tests of whether the color bimodality widely observed in GC systems generally reflects a true metallicity bimodality. Color bimodality has alternatively been attributed to a strongly nonlinear color-metallicity relation reflecting the influence of hot horizontal-branch stars. Here, we couple Subaru Suprime-Cam gi photometry with Keck/DEIMOS spectroscopy to accurately measure GC colors and a CaT index that measures the Ca II triplet. We find the NGC 3115 GC system to …

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The Sluggs Survey: Globular Cluster System Kinematics And Substructure In Ngc 4365, C. Blom, D. A. Forbes, J. P. Brodie, C. Foster, Aaron J. Romanowsky, L. R. Spitler, J. Strader Jan 2012

The Sluggs Survey: Globular Cluster System Kinematics And Substructure In Ngc 4365, C. Blom, D. A. Forbes, J. P. Brodie, C. Foster, Aaron J. Romanowsky, L. R. Spitler, J. Strader

Faculty Publications

We present a kinematic analysis of the globular cluster (GC) system of the giant elliptical galaxy NGC 4365 and find several distinct kinematic substructures. This analysis is carried out using radial velocities for 269 GCs, obtained with the DEIMOS (DEep Imaging Multi-Object Spectrograph) instrument on the Keck II telescope as part of the SAGES Legacy Unifying Globulars and Galaxies Survey (SLUGGS). We find that each of the three (formerly identified) GC colour subpopulations reveal distinct rotation properties. The rotation of the green GC subpopulation is consistent with the bulk of NGC 4365's stellar light, which ‘rolls’ about the photometric major …

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The Sluggs Survey: Calcium Triplet-Based Spectroscopic Metallicites For Over 900 Globular Clusters, C. Usher, D. A. Forbes, J. P. Brodie, C. Foster, L. R. Spitler, J. A. Arnold, Aaron J. Romanowsky, J. Strader, V. Pota Jan 2012

The Sluggs Survey: Calcium Triplet-Based Spectroscopic Metallicites For Over 900 Globular Clusters, C. Usher, D. A. Forbes, J. P. Brodie, C. Foster, L. R. Spitler, J. A. Arnold, Aaron J. Romanowsky, J. Strader, V. Pota

Faculty Publications

Although the colour distribution of globular clusters in massive galaxies is well known to be bimodal, the spectroscopic metallicity distribution has been measured in only a few galaxies. After redefining the calcium triplet index–metallicity relation, we use our relation to derive the metallicity of 903 globular clusters in 11 early-type galaxies. This is the largest sample of spectroscopic globular cluster metallicities yet assembled. We compare these metallicities with those derived from Lick indices finding good agreement. In six of the eight galaxies with sufficient numbers of high-quality spectra we find bimodality in the spectroscopic metallicity distribution. Our results imply that …

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The Globular Cluster System Of Ngc 1316 - Ii. The Extraordinary Object Sh2, T. Richtler, B. Kumar, L. Bassino, B. Dirsch, Aaron J. Romanowsky Jan 2012

The Globular Cluster System Of Ngc 1316 - Ii. The Extraordinary Object Sh2, T. Richtler, B. Kumar, L. Bassino, B. Dirsch, Aaron J. Romanowsky

Faculty Publications

Context. SH2 has been described as an isolated HII-region, located about 6.5′ south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the outskirts of the Fornax cluster of galaxies. Aims. We give a first, preliminary description of the stellar content and environment of this remarkable object. Methods. We used photometric data in the Washington system and HST photometry from the Hubble Legacy Archive for a morphological description and preliminary aperture photometry. Low-resolution spectroscopy provides radial velocities of the brightest star cluster in SH2 and a nearby intermediate-age cluster. Results. SH2 is not a normal HII-region, …

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Kinematic Properties Of The Field Elliptical Ngc 7507, R. Salinas, T. Richtler, L. P. Bassino, Aaron J. Romanowsky, Y. Schuberth Jan 2012

Kinematic Properties Of The Field Elliptical Ngc 7507, R. Salinas, T. Richtler, L. P. Bassino, Aaron J. Romanowsky, Y. Schuberth

Faculty Publications

The dark matter (DM) halos of field elliptical galaxies have not been well-studied and their properties appear controversial in the literature. While some galaxies appear to be nearly devoid of DM, others show clear evidence of its presence. Furthermore, modified Newtonian dynamics (MOND), which has been found to have predictive power in the domain of disk galaxies, has not yet been investigated for isolated elliptical galaxies. We study the kinematics of the isolated elliptical NGC 7507, which has been claimed as a clear example of DM presence in early-type galaxies. We obtained major and minor axis long-slit spectroscopy of NGC …

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Angular Momentum And Galaxy Formation Revisited, Aaron J. Romanowsky, S. M. Fall Jan 2012

Angular Momentum And Galaxy Formation Revisited, Aaron J. Romanowsky, S. M. Fall

Faculty Publications

Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j sstarf and mass M sstarf (thus extending earlier work by Fall). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as 10 effective radii, and find that data at two effective radii are …

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Spider - Vi. The Central Dark Matter Content Of Luminous Early-Type Galaxies: Benchmark Correlations With Mass, Structural Parameters And Environment, C. Tortora, F. La Barbera, N. R. Napolitano, R. R. De Carvalho, Aaron J. Romanowsky Jan 2012

Spider - Vi. The Central Dark Matter Content Of Luminous Early-Type Galaxies: Benchmark Correlations With Mass, Structural Parameters And Environment, C. Tortora, F. La Barbera, N. R. Napolitano, R. R. De Carvalho, Aaron J. Romanowsky

Faculty Publications

We analyze the central dark-matter (DM) content of \sim 4,500 massive (M* \gsim 10^{10} Msun), low-redshift (z<0.1), early-type galaxies (ETGs), with high-quality ugrizYJHK photometry and optical spectroscopy from SDSS and UKIDSS. We estimate the "central" fraction of DM within the K-band effective radius, \Re, using spherically symmetric isotropic galaxy models. We discuss the role of systematics. The main results of the present work are the following: (1) DM fractions increase systematically with both structural parameters and mass proxies, as in previous studies, and decrease with central stellar density. 2) All correlations involving DM fractions are caused by two fundamental ones with galaxy effective radius and central velocity dispersion. These correlations are independent of each other, so that ETGs populate a central-DM plane (DMP), i.e. a correlation among fraction of total-to-stellar mass, effective radius, and velocity dispersion, whose scatter along the total-to-stellar mass axis amounts to \sim 0.15 dex. (3) In general, under the assumption of an isothermal or a constant M/L profile for the total mass distribution, a Chabrier IMF is favoured with respect to a bottom-heavier Salpeter IMF, as the latter produces negative (i.e. unphysical) DM fractions for more than 50% of the galaxies in our sample. For a Chabrier IMF, the DM estimates agree with \LambdaCDM toy-galaxy models based on contracted DM-halo density profiles. We also find agreement with predictions from hydrodynamical simulations. (4) The central DM content of ETGs does not depend significantly on the environment where galaxies reside, with group and field ETGs having similar DM trends.

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Short-Range Correlations And Cooling Of Ultracold Fermions In The Honeycomb Lattice, Baoming Tang, Thereza Paiva, Ehsan Khatami, Marcos Rigol Jan 2012

Short-Range Correlations And Cooling Of Ultracold Fermions In The Honeycomb Lattice, Baoming Tang, Thereza Paiva, Ehsan Khatami, Marcos Rigol

Faculty Publications

We use determinantal quantum Monte Carlo simulations and numerical linked-cluster expansions to study thermodynamic properties and short-range spin correlations of fermions in the honeycomb lattice. We find that, at half filling and finite temperatures, nearest-neighbor spin correlations can be stronger in this lattice than in the square lattice, even in regimes where the ground state in the former is a semimetal or a spin liquid. The honeycomb lattice also exhibits a more pronounced anomalous region in the double occupancy that leads to stronger adiabatic cooling than in the square lattice. We discuss the implications of these findings for optical lattice …

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Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream Around Ngc 4449 And Hierarchical Galaxy Formation On Small Scales, D. Mart´Inez-Delgado, Aaron J. Romanowsky, R. J. Gabany, F. Annibali, J. A. Arnold, J. Fliri, S. Zibetti, R. P. Van Der Marel, H. W. Rix, T. S. Chonis, J. A. Carballo-Bello, A. Aloisi, A. V. Macci`O, J. Gallego-Laborda, J. P. Brodie, M. R. Merrifield Jan 2012

Dwarfs Gobbling Dwarfs: A Stellar Tidal Stream Around Ngc 4449 And Hierarchical Galaxy Formation On Small Scales, D. Mart´Inez-Delgado, Aaron J. Romanowsky, R. J. Gabany, F. Annibali, J. A. Arnold, J. Fliri, S. Zibetti, R. P. Van Der Marel, H. W. Rix, T. S. Chonis, J. A. Carballo-Bello, A. Aloisi, A. V. Macci`O, J. Gallego-Laborda, J. P. Brodie, M. R. Merrifield

Faculty Publications

A candidate diffuse stellar substructure was previously reported in the halo of the nearby dwarf starburst galaxy NGC 4449 by Karachentsev et al. We map and analyze this feature using a unique combination of deep integrated-light images from the BlackBird 0.5 m telescope, and high-resolution wide-field images from the 8 m Subaru Telescope, which resolve the nebulosity into a stream of red giant branch stars, and confirm its physical association with NGC 4449. The properties of the stream imply a massive dwarf spheroidal progenitor, which after complete disruption will deposit an amount of stellar mass that is comparable to the …

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The Ongoing Assembly Of A Central Cluster Galaxy: Phase-Space Substructures In The Halo Of M87, Aaron J. Romanowsky, J. Strader, J. P. Brodie, C. Mihos, L. R. Spitler, D. A. Forbes, C. Foster, J. A. Arnold Jan 2012

The Ongoing Assembly Of A Central Cluster Galaxy: Phase-Space Substructures In The Halo Of M87, Aaron J. Romanowsky, J. Strader, J. P. Brodie, C. Mihos, L. R. Spitler, D. A. Forbes, C. Foster, J. A. Arnold

Faculty Publications

The halos of galaxies preserve unique records of their formation histories. We carry out the first combined observational and theoretical study of phase-space halo substructure in an early-type galaxy: M87, the central galaxy in the Virgo cluster. We analyze an unprecedented wide-field, high-precision photometric and spectroscopic data set for 488 globular clusters (GCs), which includes new, large-radius Subaru/Suprime-Cam and Keck/DEIMOS observations. We find signatures of two substructures in position-velocity phase space. One is a small, cold stream associated with a known stellar filament in the outer halo; the other is a large shell-like pattern in the inner halo that implies …

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Radially Extended Kinematics In The S0 Galaxy Ngc 2768 From Planetary Nebulae, Globular Clusters And Starlight, D. A. Forbes, A. Cortesi, V. Pota, C. Foster, Aaron J. Romanowsky, M. R. Merrifield, J. P. Strader, L. Coccato, N. Napolitano Jan 2012

Radially Extended Kinematics In The S0 Galaxy Ngc 2768 From Planetary Nebulae, Globular Clusters And Starlight, D. A. Forbes, A. Cortesi, V. Pota, C. Foster, Aaron J. Romanowsky, M. R. Merrifield, J. P. Strader, L. Coccato, N. Napolitano

Faculty Publications

There are only a few tracers available to probe the kinematics of individual early-type galaxies beyond one effective radius. Here we directly compare a sample of planetary nebulae (PNe), globular clusters (GCs) and galaxy starlight velocities out to approximately four effective radii, in the S0 galaxy NGC 2768. Using a bulge-to-disc decomposition of a K-band image we assign PNe and starlight to either the disc or the bulge. We show that the bulge PNe and bulge starlight follow the same radial density distribution as the red subpopulation of GCs, whereas the disc PNe and disc starlight are distinct components. We …

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Directional Limits On Persistent Gravitational Waves Using Ligo S5 Science Data, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, P. Ajith, B. Allen, G. S. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, M. A. Arain, M. C. Araya, M. Aronsson, K. G. Arun, Y. Aso, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, S. Ballmer, D. Barker, Tiffany Z. Summerscales Dec 2011

Directional Limits On Persistent Gravitational Waves Using Ligo S5 Science Data, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, P. Ajith, B. Allen, G. S. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, M. A. Arain, M. C. Araya, M. Aronsson, K. G. Arun, Y. Aso, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, S. Ballmer, D. Barker, Tiffany Z. Summerscales

Faculty Publications

The gravitational-wave (GW) sky may include nearby pointlike sources as well as stochastic backgrounds. We perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. Finding no evidence to support the detection of GWs, we present 90% confidence level (C.L.) upper-limit maps of GW strain power with typical values between 2-20×10-50strain2Hz-1 and 5-35×10 -49strain2Hz-1sr-1 for pointlike and extended sources, respectively. The latter result is the first of its kind. We also set 90% C.L. limits on the narrow-band root-mean-square GW strain from interesting targets …

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Ordered Phases In Ruthenium Binary Alloys From High-Throughput First-Principles Calculations, Gus L. W. Hart, Lance J. Nelson, Michal Jahnátek, Ohad Levy, Roman V. Chepulskii, J. Xue, Stephano Curtarolo Dec 2011

Ordered Phases In Ruthenium Binary Alloys From High-Throughput First-Principles Calculations, Gus L. W. Hart, Lance J. Nelson, Michal Jahnátek, Ohad Levy, Roman V. Chepulskii, J. Xue, Stephano Curtarolo

Faculty Publications

Despite the increasing importance of ruthenium in numerous technological applications, e.g., catalysis and electronic devices, experimental and computational data on its binary alloys are sparse. In particular, data are scant on those binary systems believed to be phase-separating. We performed a comprehensive study of ruthenium binary systems with the 28 transition metals, using high-throughput first-principles calculations. These computations predict novel unsuspected compounds in 7 of the 16 binary systems previously believed to be phase-separating and in two of the three systems reported with only a high-temperature σ phase. They also predict a few unreported compounds in five additional systems and …

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Thermodynamics And Phase Transitions For The Heisenberg Model On The Pinwheel Distorted Kagome Lattice, Ehsan Khatami, Rajiv Singh, Marcos Rigol Dec 2011

Thermodynamics And Phase Transitions For The Heisenberg Model On The Pinwheel Distorted Kagome Lattice, Ehsan Khatami, Rajiv Singh, Marcos Rigol

Faculty Publications

We study the Heisenberg model on the pinwheel distorted kagome lattice as observed in the material Rb2Cu3SnF12. Experimentally relevant thermodynamic properties at finite temperatures are computed utilizing numerical linked-cluster expansions. We also develop a Lanczos-based, zero-temperature, numerical linked-cluster expansion to study the approach of the pinwheel distorted lattice to the uniform kagome-lattice Heisenberg model. We find strong evidence for a phase transition before the uniform limit is reached, implying that the ground state of the kagome-lattice Heisenberg model is likely not pinwheel dimerized and is stable to finite pinwheel-dimerizing perturbations.

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Thermodynamics Of Strongly Interacting Fermions In Two-Dimensional Optical Lattices, Ehsan Khatami, Marcos Rigol Nov 2011

Thermodynamics Of Strongly Interacting Fermions In Two-Dimensional Optical Lattices, Ehsan Khatami, Marcos Rigol

Faculty Publications

We study finite-temperature properties of strongly correlated fermions in two-dimensional optical lattices by means of numerical linked cluster expansions, a computational technique that allows one to obtain exact results in the thermodynamic limit. We focus our analysis on the strongly interacting regime, where the on-site repulsion is of the order of or greater than the band width. We compute the equation of state, double occupancy, entropy, uniform susceptibility, and spin correlations for temperatures that are similar to or below the ones achieved in current optical lattice experiments. We provide a quantitative analysis of adiabatic cooling of trapped fermions in two …

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Hubble Space Telescope Imaging Of Post-Starburst Quasars, S. Cales, M. Brotherton, Zhaohui Shang, Vardha Bennert, Gabriela Canalizo, R. Stoll, R. Ganguly, D. Berk, Cassandra Paul, A. Diamond-Stanic Oct 2011

Hubble Space Telescope Imaging Of Post-Starburst Quasars, S. Cales, M. Brotherton, Zhaohui Shang, Vardha Bennert, Gabriela Canalizo, R. Stoll, R. Ganguly, D. Berk, Cassandra Paul, A. Diamond-Stanic

Faculty Publications

We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (Mburst ∼ 1010 M⊙), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN–starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the …

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Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo Aug 2011

Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo

Faculty Publications

Magnesium alloys are among the lightest structural materials known and are of considerable technological interest. To develop superior magnesium alloys, experimentalists must have a thorough understanding of the concentration-dependent precipitates that form in a given system, and hence, the thermodynamic stability of crystal phases must be determined. This information is often lacking but can be supplied by first-principles methods. Within the high-throughput framework, AFLOW, T = 0 K ground-state predictions are made by scanning a large set of known candidate structures for thermodynamic (formation energy) minima. The following 34 systems are investigated: AlMg, AuMg, CaMg, CdMg, CuMg, FeMg , GeMg, …

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Search For Gravitational Wave Bursts From Six Magnetars, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt, B. Allen, G. S. Allen, E. Amador Ceron, D. Amariutei, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, K. Arai, M. A. Arain, M. C. Araya, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, B. E. Aylott, S. Babak, P. Baker, G. Ballardin, S. Ballmer, D. Barker, Tiffany Z. Summerscales Jun 2011

Search For Gravitational Wave Bursts From Six Magnetars, J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt, B. Allen, G. S. Allen, E. Amador Ceron, D. Amariutei, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, K. Arai, M. A. Arain, M. C. Araya, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, B. E. Aylott, S. Babak, P. Baker, G. Ballardin, S. Ballmer, D. Barker, Tiffany Z. Summerscales

Faculty Publications

Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely 1kpc from Earth, an order of magnitude closer …

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A Layer Correlation Technique For Pion Energy Calibration At The 2004 Atlas Combined Beam Test, E. Abat, J M. Abdallah, T N. Addy, P Adragna, M Aharrouche, A Ahmad, T Pa Akesson, M Aleksa, C Alexa, K Anderson, A Andreazza, F Anghinolfi, A Antonaki, G Arabize, E Arik, T Atkinson, J Baines, O K. Baker, D Banfi, S Baron, Roberto Petti, Et. Al. Jun 2011

A Layer Correlation Technique For Pion Energy Calibration At The 2004 Atlas Combined Beam Test, E. Abat, J M. Abdallah, T N. Addy, P Adragna, M Aharrouche, A Ahmad, T Pa Akesson, M Aleksa, C Alexa, K Anderson, A Andreazza, F Anghinolfi, A Antonaki, G Arabize, E Arik, T Atkinson, J Baines, O K. Baker, D Banfi, S Baron, Roberto Petti, Et. Al.

Faculty Publications

A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 …

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Thermodynamics Of The Antiferromagnetic Heisenberg Model On The Checkerboard Lattice, Ehsan Khatami, Maros Rigol Apr 2011

Thermodynamics Of The Antiferromagnetic Heisenberg Model On The Checkerboard Lattice, Ehsan Khatami, Maros Rigol

Faculty Publications

Employing numerical linked-cluster expansions (NLCEs) along with exact diagonalizations of finite clusters with periodic boundary condition, we study the energy, specific heat, entropy, and various susceptibilities of the antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined with extrapolation techniques, allow us to access temperatures much lower than those accessible to exact diagonalization and other series expansions. We show that the high-temperature peak in specific heat decreases as the frustration increases, consistent with the large amount of unquenched entropy in the region around maximum classical frustration, where the nearest-neighbor and next-nearest-neighbor exchange interactions (J and J′, respectively) have the same …

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Photon Reconstruction In The Atlas Inner Detector And Liquid Argon Barrel Calorimeter At The 2004 Combined Test Beam, E. Abat, J. M. Abdallah, T. N. Addy, P. Adragna, M. Aharrouche, A. Ahmad, T. P. Akesson, M. Aleksa, C. Alexa, K. Anderson, A. Andreazza, F. Anghinolf, A. Antonaki, G. Arabidze, E. Arik, T. Atkinson, J. Baines, O. K. Baker, D. Banfi, S. Baron, Roberto Petti, Et. Al. Apr 2011

Photon Reconstruction In The Atlas Inner Detector And Liquid Argon Barrel Calorimeter At The 2004 Combined Test Beam, E. Abat, J. M. Abdallah, T. N. Addy, P. Adragna, M. Aharrouche, A. Ahmad, T. P. Akesson, M. Aleksa, C. Alexa, K. Anderson, A. Andreazza, F. Anghinolf, A. Antonaki, G. Arabidze, E. Arik, T. Atkinson, J. Baines, O. K. Baker, D. Banfi, S. Baron, Roberto Petti, Et. Al.

Faculty Publications

The reconstruction of photons in the ATLAS detector is studied with data taken during the 2004 Combined Test Beam, where a full slice of the ATLAS detector was exposed to beams of particles of known energy at the CERN SPS. The results presented show significant differences in the longitudinal development of the electromagnetic shower between converted and unconverted photons as well as in the total measured energy. The potential to use the reconstructed converted photons as a means to precisely map the material of the tracker in front of the electromagnetic calorimeter is also considered. All results obtained are compared …

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Polymer Molded Templates For Nanostructured Amorphous Silicon Photovoltaics, Lei Pei, Amy Balls, Cary Tippets, Jonathan Abbott, Matthew R. Linford, David D. Allred, Richard R. Vanfleet, Robert C. Davis, Jian Hu, Arun Madan Apr 2011

Polymer Molded Templates For Nanostructured Amorphous Silicon Photovoltaics, Lei Pei, Amy Balls, Cary Tippets, Jonathan Abbott, Matthew R. Linford, David D. Allred, Richard R. Vanfleet, Robert C. Davis, Jian Hu, Arun Madan

Faculty Publications

Here, the authors report the fabrication of transparent polymer templates for nanostructured amorphous silicon photovoltaics using low-cost nanoimprint lithography of polydimethylsiloxane. The template contains a square two-dimensional array of high-aspect-ratio nanoholes (300 nm diameter by 1 µm deep holes) on a 500X500 nm^2 pitch. A 100 nm thick layer of a-Si:H was deposited on the template surface resulting in a periodically nanostructured film. The optical characterization of the nanopatterned film showed lower light transmission at 600-850 nm wavelengths and lower light reflection at 400-650 nm wavelengths, resulting in 20% higher optical absorbance at AM 1.5 spectral irradiance versus a nonpatterned …

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Search For Gravitational Waves Associated With The August 2006 Timing Glitch Of The Vela Pulsar, J. Abadie, B. P. Abbott, R. Abbott, R. Adhikari, P. Ajith, B. Allen, G. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, M. A. Arain, M. Araya, Y. Aso, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, S. Ballmer, D. Barker, B. Barr, P. Barriga, L. Barsotti, M. A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, B. Behnke, M. Benacquista, M. F. Bennett, Tiffany Z. Summerscales Feb 2011

Search For Gravitational Waves Associated With The August 2006 Timing Glitch Of The Vela Pulsar, J. Abadie, B. P. Abbott, R. Abbott, R. Adhikari, P. Ajith, B. Allen, G. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, M. A. Arain, M. Araya, Y. Aso, S. Aston, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, S. Ballmer, D. Barker, B. Barr, P. Barriga, L. Barsotti, M. A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, B. Behnke, M. Benacquista, M. F. Bennett, Tiffany Z. Summerscales

Faculty Publications

The physical mechanisms responsible for pulsar timing glitches are thought to excite quasinormal mode oscillations in their parent neutron star that couple to gravitational-wave emission. In August 2006, a timing glitch was observed in the radio emission of PSR B0833-45, the Vela pulsar. At the time of the glitch, the two colocated Hanford gravitational-wave detectors of the Laser Interferometer Gravitational-wave observatory (LIGO) were operational and taking data as part of the fifth LIGO science run (S5). We present the first direct search for the gravitational-wave emission associated with oscillations of the fundamental quadrupole mode excited by a pulsar timing glitch. …

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Unravelling The Origins Of S0 Galaxies Using Maximum Likelihood Analysis Of Planetary Nebulae Kinematics, A. Cortesi, M. R. Merrifield, M. Arnaboldi, O. Gerhard, I. Martinez-Valpuesta, K. Saha, L. Coccato, S. Bamford, N. R. Napolitano, N. G. Douglas, Aaron J. Romanowsky, K. Kuijken, M. Capaccioli, K. C. Freeman Jan 2011

Unravelling The Origins Of S0 Galaxies Using Maximum Likelihood Analysis Of Planetary Nebulae Kinematics, A. Cortesi, M. R. Merrifield, M. Arnaboldi, O. Gerhard, I. Martinez-Valpuesta, K. Saha, L. Coccato, S. Bamford, N. R. Napolitano, N. G. Douglas, Aaron J. Romanowsky, K. Kuijken, M. Capaccioli, K. C. Freeman

Faculty Publications

To investigate the origins of S0 galaxies, we present a new method of analysing their stellar kinematics from discrete tracers such as planetary nebulae. This method involves binning the data in the radial direction so as to extract the most general possible non-parametric kinematic profiles, and using a maximum-likelihood fit within each bin in order to make full use of the information in the discrete kinematic tracers. Both disc and spheroid kinematic components are fitted, with a two-dimensional decomposition of imaging data used to attribute to each tracer a probability of membership in the separate components. Likelihood clipping also allows …

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The Pn.S Elliptical Galaxy Survey: A Standard Cdm Halo Around Ngc 4374?, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, N. G. Douglas, M. Arnaboldi, L. Coccato, O. Gerhard, K. Kuijken, M. R. Merrifield, S. P. Bamford, A. Cortesi, P. Das, K. C. Freeman Jan 2011

The Pn.S Elliptical Galaxy Survey: A Standard Cdm Halo Around Ngc 4374?, N. R. Napolitano, Aaron J. Romanowsky, M. Capaccioli, N. G. Douglas, M. Arnaboldi, L. Coccato, O. Gerhard, K. Kuijken, M. R. Merrifield, S. P. Bamford, A. Cortesi, P. Das, K. C. Freeman

Faculty Publications

As part of our current programme to test ΛCDM predictions for dark matter (DM) haloes using extended kinematical observations of early-type galaxies, we present a dynamical analysis of the bright elliptical galaxy NGC 4374 (M84) based on ∼450 planetary nebulae (PNe) velocities from the PN.Spectrograph, along with extended long-slit stellar kinematics. This is the first such analysis of a galaxy from our survey with a radially constant velocity dispersion profile. We find that the spatial and kinematical distributions of the PNe agree with the field stars in the region of overlap. The velocity kurtosis is consistent with zero at almost …

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Stellar Mass-To-Light Ratio Gradients In Galaxies: Correlations With Mass, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, Ph. Jetzer, V. F. Cardone, M. Capaccioli Jan 2011

Stellar Mass-To-Light Ratio Gradients In Galaxies: Correlations With Mass, C. Tortora, N. R. Napolitano, Aaron J. Romanowsky, Ph. Jetzer, V. F. Cardone, M. Capaccioli

Faculty Publications

We analyse the stellar mass-to-light ratio (M/L) gradients in a large sample of local galaxies taken from the Sloan Digital Sky Survey, spanning a wide range of stellar masses and morphological types. As suggested by the well-known relationship between M/L values and colours, we show that M/L gradients are strongly correlated with colour gradients, which we trace to the effects of age variations. Stellar M/L gradients generally follow patterns of variation with stellar mass and galaxy type that were previously found for colour and metallicity gradients. In late-type galaxies M/L gradients are negative, steepening with increasing mass. In early-type galaxies …

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An Extremely Luminous Panchromatic Outburst From The Nucleus Of A Distant Galaxy, A. J. Levan, N. R. Tanvir, S. B. Cenko, D. A. Perley, K. Wiersema, J. S. Bloom, A. S. Fruchter, A. De Urgarte Postigo, P. T. Butler, A. J. Van Der Horst, G. Leloudas, A. N. Morgan, K. Misra, G. C. Bower, J. Farihi, R. L. Tunnicliffe, A. N. Morgan, K. Misra, G. C. Bower, J. Farihi, R. L. Tunnicliffe, M. Modjaz, J. M. Silverman, J. Hjorth, C. Thone, A. Cucchiara, J. M. Castro-Ceron, A. J. Castro-Tirado, J. A. Arnold, M. Bremer, J. P. Brodie, T. Carroll, M. C. Cooper, P. A. Curran, R. M. Cutri, J. Ehle, D. Forbes, J. Fynbo, J. Gorosabel, J. Graham, D. I. Hoffman, S. Guziy, P. Jakobsson, A. Kamble, T. Kerr, M. M. Kasliwal, C. Kouveliotou, D. Kocevski, N. M. Law, P. E. Nugent, E. O. Ofek, D. Poznanski, R. M. Quimby, E. Rol, Aaron J. Romanowsky, R. Sanchez-Ramirez, S. Schulze, N. Singh, L. Van Spaandonk, R.L.C. Starling, R. G. Strom, J. C. Tello, O. Vaduvescu, P. J. Wheatley, J. M. Winters, R.A.M.J. Wijers, D. Xu Jan 2011

An Extremely Luminous Panchromatic Outburst From The Nucleus Of A Distant Galaxy, A. J. Levan, N. R. Tanvir, S. B. Cenko, D. A. Perley, K. Wiersema, J. S. Bloom, A. S. Fruchter, A. De Urgarte Postigo, P. T. Butler, A. J. Van Der Horst, G. Leloudas, A. N. Morgan, K. Misra, G. C. Bower, J. Farihi, R. L. Tunnicliffe, A. N. Morgan, K. Misra, G. C. Bower, J. Farihi, R. L. Tunnicliffe, M. Modjaz, J. M. Silverman, J. Hjorth, C. Thone, A. Cucchiara, J. M. Castro-Ceron, A. J. Castro-Tirado, J. A. Arnold, M. Bremer, J. P. Brodie, T. Carroll, M. C. Cooper, P. A. Curran, R. M. Cutri, J. Ehle, D. Forbes, J. Fynbo, J. Gorosabel, J. Graham, D. I. Hoffman, S. Guziy, P. Jakobsson, A. Kamble, T. Kerr, M. M. Kasliwal, C. Kouveliotou, D. Kocevski, N. M. Law, P. E. Nugent, E. O. Ofek, D. Poznanski, R. M. Quimby, E. Rol, Aaron J. Romanowsky, R. Sanchez-Ramirez, S. Schulze, N. Singh, L. Van Spaandonk, R.L.C. Starling, R. G. Strom, J. C. Tello, O. Vaduvescu, P. J. Wheatley, J. M. Winters, R.A.M.J. Wijers, D. Xu

Faculty Publications

Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray–selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy …

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