115177789
Scalar field dynamics in warped AdS3 black hole background
Abstract We study the normal modes of a scalar field in the background of a warped AdS 3 black hole which arises in topologically massive gravity. We discuss the normal mode spectrum using the brick wall boundary condition. In addition, we investigate the possibility of a more general boundary condition for the scalar field.
13926216
Asymptotic Quasinormal Modes of d-Dimensional Schwarzschild Black Hole with Gauss-Bonnet Correction
We obtain an analytic expression for the highly damped asymptotic quasinormal mode frequencies of the (d ≥ 5)-dimensional Schwarzschild black hole modified by the Gauss–Bonnet term, which appears in string derived models of gravity. The analytic expression is obtained under the string inspired assumption that there exists a minimum length scale in the system and in the limit when the coupling in front of the Gauss–Bonnet term in the action is small. Although there are several similarities of this geometry with that of the Schwarzschild black hole, the asymptotic quasinormal mode frequencies are quite different. In particular, the real part of the asymptotic quasinormal frequencies for this class of single horizon black holes is not proportional to log(3).
119208028
BLACK HOLE PHASE TRANSITIONS VIA BRAGG–WILLIAMS
We argue that a convenient way to analyze instabilities of black holes in AdS space is via Bragg–Williams construction of a free energy function. Starting with a pedagogical review of this construction in condensed matter systems and also its implementation to Hawking–Page transition, we study instabilities associated with hairy black holes and also with the R-charged black holes. For the hairy black holes, an analysis of thermal quench is presented.
16207690
Quasinormal modes for tensor and vector type perturbation of Gauss Bonnet black hole using third order WKB approach
We obtain the quasinormal modes for tensor perturbations of Gauss–Bonnet (GB) black holes in d = 5, 7, 8 dimensions and vector perturbations in d =  5, 6, 7 and 8 dimensions using third order WKB formalism. The tensor perturbation for black holes in d = 6 is not considered because of the fact that the black hole is unstable to tensor mode perturbations. In the case of uncharged GB black hole, for both tensor and vector perturbations, the real part of the QN frequency increases as the Gauss–Bonnet coupling (α′) increases. The imaginary part first decreases upto a certain value of α′ and then increases with α′ for both tensor and vector perturbations. For larger values of α′, the QN frequencies for vector perturbation differs slightly from the QN frequencies for tensorial one. It has also been shown that as α′ → 0, the quasinormal frequencies for tensor and vector perturbations of the Schwarzschild black hole can be obtained. We have also calculated the quasinormal spectrum of the charged GB black hole for tensor perturbations. Here we have found that the real oscillation frequency increases, while the imaginary part of the frequency falls with the increase of the charge. We also show that the quasinormal frequencies for scalar field perturbations and the tensor gravitational perturbations do not match as was claimed in the literature. The difference in the result increases if we increase the GB coupling.
118709858
Viscosity to entropy ratio at extremality
Assuming gauge theory realization at the boundary, we show that the viscosity to entropy ratio is 1/(4π) where the bulk is represented by a large class of extremal black holes in anti-deSitter space. In particular, this class includes multiple R-charged black holes in various dimensions.
119199231
Normal-mode analysis for scalar fields in BTZ black-hole background
We analyze the possibility of inequivalent boundary conditions for a scalar field propagating in the BTZ black-hole space-time. We find that for certain ranges of the black-hole parameters, the Klein–Gordon operator admits a one-parameter family of self-adjoint extensions. For this range, the BTZ space-time is not quantum mechanically complete. We suggest a physically motivated method for determining the spectra of the Klein–Gordon operator.
118956575
Simulating Merging Galaxies: The Infrared View
We calculate multi-wavelength spectral energy distributions (SEDs) (spanning optical to millimeter wavelengths) from simulations of major galaxy mergers using a three-dimensional radiative transfer code, which treats the absorption and scattering of radiation as well as the reemission from dust grains self-consistently. These calculations allow us to deduce correlations from the X-rays to millimeter wavelengths. We confirm observed correlations for Spitzer Space Telescope’s IRAC bands, as well as correlations observed in the IRAS era. We also make predictions that should be testable by future instruments. The power of the dynamical approach afforded by calculating fluxes from the merger simulations is that we can directly correlate observed clustering in the data as seen in IRAC color-color plots with the relative amount of time the system spends in a region of color-color space. We also present photo albums spanning the lifetime of SMGs, from its infancy in the pre-merger phase to its final stage as an elliptical galaxy, as seen in various bands. Finally, we compare the SEDs from the simulations to recent observations of SMGs. Our calculations, which match observed correlations both for local ULIRGs and higher redshift systems, suggest that simulations of major mergers with black hole feedback provide an excellent framework within which to understand the emission from local ULIRGs, and their high redshift cousins, the submillimeter galaxies.
15170029
PANCHROMATIC SPECTRAL ENERGY DISTRIBUTIONS OF DUSTY GALAXIES WITH RADISHE. I. PREDICTIONS FOR HERSCHEL: CORRELATING COLORS WITH GALACTIC ENERGY SOURCES
We present three-dimensional, self-consistent radiative transfer solutions with a new Monte Carlo radiative equilibrium code. The code RADISHE can be applied to calculate the emergent spectral energy distributions (SEDs) and broadband images from optical to millimeter wavelengths of arbitrary density geometries with distributed sources of radiation. One of the primary uses of this code has been to interface with hydrodynamical codes to calculate emergent SEDs along a simulation time sequence. We focus the applications of this code in this paper on infrared bright dusty galaxies, but RADISHE is also ideal for calculating emission from star clusters or protostellar environments. The primary methodological focus of this paper is on the radiative equilibrium temperature calculation. We find that an iterative calculation of the temperature, which takes the sum of photon flight paths as the Monte Carlo estimator for the mean free intensity, is significantly faster than relaxation temperature calculation methods, particularly when large numbers of grid cells are required (i.e., in modeling three-dimensional geometries such as the dust envelopes of turbulent massive protostellar cores or infrared-bright galaxies). An accurate long-wavelength SED and corresponding temperature calculation will be essential for analyzing upcoming Herschel Space Observatory observations. We present simulated color-color plots for infrared-bright galaxies at a range of redshifts, and unfold these plots as color versus the fractional active galactic nucleus (AGN) luminosity, to demonstrate that Herschel will be able to effectively discriminate between submillimeter galaxies, where the energy source is dominated by AGN, and those where star formation dominates. We demarcate in particular the Class II or energetically active AGN evolutionary phase in Herschel color-color plots.
123616864
Tidal imprints of a dark subhalo on the outskirts of the Milky Way
We study the dynamical evolution of spiral structure in the stellar disks of isolated galaxies using high resolution Smoothed Particle Hydrodynamics (SPH) simulations that treat the evolution of gas, stars, and dark matter self-consistently. We focus this study on the question of self-excited spiral structure in the stellar disk and inves tigate the dynamical coupling between the cold, dissipative gaseous component and the stellar component. We find that angular momentum transport from the gas to the stars inside of corotation leads to a roughly time-steady spiral structure in the stellar disk. To make this point clea r, we contrast these results with otherwise identical simulations that do not include a cold gaseous component that is able to cool radiatively and dissipate energy, and find that spiral struc ture, when it is incipient, dies out more rapidly in simulations that do not include gas. We also employ a standard star formation prescription to convert gas into stars and find that our resul ts hold for typical gas consumption time scales that are in accord with the Kennicutt-Schmidt relation. We therefore attribute the long-lived roughly time steady spiral structure in the stel lar disk to the dynamical coupling between the gas and the stars and the resultant torques that t he self-gravitating gaseous disk is able to exert on the stars due to an azimuthal phase shift be tween the collisionless and dissipative components. Spiral galaxies present two faces to observers. When seen in blue light, these galaxies look disordered, with spurs, branche s and feather-like structures seen even in grand design galaxies , while K-band images show that these galaxies possess smooth, usually two-armed spiral patterns. We study here the dynamical interaction between the Population I component seen in blue light and the older Population II component revealed in the longer wavelengths, specifically with the intent of understanding how the intera ction between the gas and the stars affects the time evolution of spiral
118705938
FINDING DWARF GALAXIES FROM THEIR TIDAL IMPRINTS
We describe ongoing work on a new method that allows one to approximately determine the mass and relative position (in galactocentric radius and azimuth) of galactic companions purely from analysis of observed disturbances in gas disks. We demonstrate the validity of this method, which we call Tidal Analysis, by applying it to local spirals with known optical companions, namely M51 and NGC 1512. These galaxies span the range from having a very low mass companion (~one-hundredth the mass of the primary galaxy) to a fairly massive companion (~one-third the mass of the primary galaxy). This approach has broad implications for many areas of astrophysics—for the indirect detection of dark matter (or dark-matter-dominated dwarf galaxies), and for galaxy evolution in its use to decipher the dynamical impact of satellites on galactic disks. Here, we provide a proof of principle of the method by applying it to infer and quantitatively characterize optically visible galactic companions of local spirals, from the analysis of observed disturbances in outer gas disks.
119086181
Geodesic deviation in Regge calculus
Geodesic deviation is the most basic manifestation of the influence of gravitational fields on matter. We investigate geodesic deviation within the framework of Regge calculus, and compare the results with the continuous formulation of general relativity on two different levels. We show that the continuum and simplicial descriptions coincide when the cumulative effect of the Regge contributions over an infinitesimal element of area is considered. This comparison provides a quantitative relation between the curvature of the continuous description and the deficit angles of Regge calculus. The results presented might also be of help in developing generic ways of including matter terms in the Regge equations.