118591147
The Challenge of the Largest Structures in the Universe to Cosmology
Large galaxy redshift surveys have long been used to constrain cosmological models and structure formation scenarios. In particular, the largest structures discovered observationally are thought to carry critical information on the amplitude of large-scale density fluctuations or homogeneity of the universe, and have often challenged the standard cosmological framework. The Sloan Great Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts doubt on the concordance cosmological model with a cosmological constant (i.e., the flat ΛCDM model). Here we show that the existence of the SGW is perfectly consistent with the ΛCDM model, a result that only our very large cosmological N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report on the discovery of a void complex in the SDSS much larger than the SGW, and show that such size of the largest void is also predicted in the ΛCDM paradigm. Our results demonstrate that an initially homogeneous isotropic universe with primordial Gaussian random phase density fluctuations growing in accordance with the general relativity can explain the richness and size of the observed large-scale structures in the SDSS. Using the HR2 simulation we predict that a future galaxy redshift survey about four times deeper or with 3 mag fainter limit than the SDSS should reveal a largest structure of bright galaxies about twice as big as the SGW.
118942465
The Arches Cluster Mass Function
We have analyzed H- and Ks-band images of the Arches cluster obtained using the NIRC2 instrument on Keck with the laser guide star adaptive optics (LGS AO) system. With the help of the LGS AO system, we were able to obtain the deepest ever photometry for this cluster and its neighborhood and derive the background-subtracted present-day mass function down to 1.3 M☉ for the 5''-9'' annulus of the cluster. We find that the previously reported turnover at 6 M☉ is simply due to a local bump in the mass function (MF), and that the MF continues to increase down to our 50% completeness limit (1.3 M☉) with a power-law exponent of Γ = -0.91 for the mass range of 1.3 < M/M☉ < 50. Our numerical calculations for the evolution of the Arches cluster show that the Γ-values for our annulus increase by 0.1-0.2 during the lifetime of the cluster and thus suggest that the Arches cluster initially had Γ of -1.0 to 1.1, which is only slightly shallower than the Salpeter value.
119456102
Theoretical isochrones with extinction in the K band. II. J - K versus K
ABSTRACT We calculate theoretical isochrones in a consistent way for five filter pairs near the J and K band atmospheric windows ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $J-K$ \end{document} , \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcom...
119489565
Core-Collapse Times of Two-Component Clusters
We examine the corecollapse times of isolated, two-mass-component star clusters using Fokker-Planck models. With initial condition of Plummer models, we find that the corecollapse times of clusters with M_1/M_2 >> 1 are well correlated with (N_1/N_2)^{1/2}(m_1/m_2)^{2} t_{rh}, where M_1/M_2 and m_1/m_2 are the light to heavy component total and individual mass ratios, respectively, N_1/N_2 is the number ratio, and t_{rh} is the initial half-mass relaxation time scale. We also find two-component cluster parameters that best match multi-component (thus more realistic) clusters with power-law mass functions.
13909300
The Stream-Stream Collision after the Tidal Disruption of a Star around a Massive Black Hole
A star can be tidally disrupted around a massive black hole. It is known that the debris forms a precessing stream, which may collide with itself. The stream collision is a key process in determining the subsequent evolution of the stellar debris: if the orbital energy is efficiently dissipated, the debris will eventually form a circular disk (or torus). In this paper, we have numerically studied such a stream collision resulting from the encounter between a 106 M☉ black hole and a 1 M☉ normal star with a pericenter radius of 100 R☉. A simple treatment for radiative cooling has been adopted for both optically thick and optically thin regions. We have found that approximately 10% to 15% of the initial kinetic energy of the streams is converted into thermal energy during the collision. The spread in angular momentum of the incoming stream is increased by a factor of 2 to 3, and such an increase, together with the decrease in kinetic energy, significantly helps the circularization process. The initial luminosity burst produced by the collision may reach as high as 1041 ergs s-1 in 104 s, after which the luminosity increases again (but slowly this time) to a steady value of a few 1040 ergs s-1 in a few times 105 s. The radiation from the system is expected to be close to Planckian, with an effective temperature of ~105 K.
17473739
Stellar collisions and mergers in the galactic center
Stars are most likely to merge or collide in regions of the highest stellar densities, and our own Galactic Center contains many stars packed into a relatively small volume -- even the ambient stellar number density in the central 50 pc is quite high, ~10^3 stars pc^{-3}. More striking, the three compact young clusters in this region have central densities as high as 10^6 stars pc^{-3}. We discuss these extreme environments and the possibility that stellar mergers and collisions have recently occured there. In particular, we predict that at least one massive star in the Arches cluster has already experienced a stellar merger in its short lifetime. Further, the Pistol Star, in the nearby Quintuplet cluster, might owe its apparent relative youth to a rejuvinating stellar merger. Finally, the apparently young stars in the central arcsecond could be products of either collisions, inducing atmospheric stripping, or mergers.
56119429
Centrality dependence of particle production in p-Pb collisions at $\sqrt{s_{\rm NN} }$= 5.02 TeV
We report measurements of the primary charged-particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at sNN=5.02TeV and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined by using different event-activity estimators, i.e., charged-particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero degree). The procedures to determine the centrality, quantified by the number of participants (Npart) or the number of nucleon-nucleon binary collisions (Ncoll) are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy-centrality classes, the Npart dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapidity of the number of participating nucleons is observed. Furthermore, at high-pT the p-Pb spectra are found to be consistent with the pp spectra scaled by Ncoll for all centrality classes. Our results represent valuable input for the study of the event-activity dependence of hard probes in p-Pb collisions and, hence, help to establish baselines for the interpretation of the Pb-Pb data.
119232936
Existence of a critical point in the phase diagram of the ideal relativistic neutral Bose gas
We explore the phase transitions of the ideal relativistic neutral Bose gas confined in a cubic box, without assuming the thermodynamic limit nor continuous approximation. While the corresponding non-relativistic canonical partition function is essentially a one-variable function depending on a particular combination of temperature and volume, the relativistic canonical partition function is genuinely a two-variable function of them. Based on an exact expression for the canonical partition function, we performed numerical computations for up to 105 particles. We report that if the number of particles is equal to or greater than a critical value, which amounts to 7616, the ideal relativistic neutral Bose gas features a spinodal curve with a critical point. This enables us to depict the phase diagram of the ideal Bose gas. The consequent phase transition is first order below the critical pressure or second order at the critical pressure. The exponents corresponding to the singularities are 1/2 and 2/3, respectively. We also verify the recently observed 'Widom line' in the supercritical region.
26647882
Development of the readout system for the K2K SciBar detector
Readout electronics for the scintillation bar tracking detector (SciBar) in the K2K neutrino oscillation experiment has been developed. SciBar has 14 336 scintillator bars in total. The deposited energy and timing of particles from neutrino interactions in the scintillator bars are measured by 64-channel multianode photo-multiplier tubes (MAPMTs). Compact custom-designed electronics to record the MAPMT signals were developed, consisting of front-end circuit boards attached to each MAPMT and back-end electronics modules sitting in a VME crate. The front-end circuit board multiplexes pulse-height information from all 64 anodes and generates a fast triggering signal. Two sets of ASICs (IDEAS VA32HDR11 and TA32CG) are employed for these functions. The bias voltages and relay of control signals are also handled on the board. The back-end electronics module controls the front-end board by providing the control, timing, and low-voltage signals. The board also digitizes the multiplexed signal from the front-end. The electronics achieves low noise of less than 0.3 photo-electrons and good linearity up to 300 (150) photo-electrons for MAPMTs at the gain of 5/spl times/10/sup 5/ (10/sup 6/).
122585803
Construction and properties of acrylic vessels in the RENO detector
Abstract The aim of the RENO (Reactor Experiment for Neutrino Oscillation) is to measure the smallest neutrino mixing angle, θ 13 . The RENO detector consists of four concentric cylindrical layers: the target, γ - catcher , buffer and veto. Acrylic is used for the target and γ - catcher vessels, both of which contain liquid scintillator. Acrylic was chosen because it has good transmittance in the wavelength range of 400 – 430 nm and also does not react with liquid-scintillating solvents. In order to reduce systematic uncertainties, the target volume should be identical to a level of less than 0.1% between the near and far detectors. Furthermore, the acrylic vessel should not have any leaks. In this paper, we investigate the optical properties, design and construction of the acrylic vessels used in the RENO detector.
118907734
Separation of the variables in the solar neutrino problem.