14325771
TIDAL IMPRINTS OF A DARK SUB-HALO ON THE OUTSKIRTS OF THE MILKY WAY. II. PERTURBER AZIMUTH
We extend our analysis of the observed disturbances on the outskirts of the H I disk of the Milky Way. We employ the additional constraints of the phase of the modes of the observed H I image and asymmetry in the radial velocity to derive the azimuth of the perturber inferred to be responsible for the disturbances in the H I disk. Specifically, we carry out a modal analysis of the phase of the disturbances in the H I image and in high-resolution smoothed particle hydrodynamics (SPH) simulations of a Milky Way like galaxy tidally interacting with dark perturbers, the relative offset of which we utilize to derive the perturber azimuth. Under the assumption that the asymmetry in the radial velocity is due to the perturber, we derive the best fit to the radial velocity at l = 0, 180, and use this constraint to also derive the perturber azimuth. To make a direct connection with observations, we express our results in Sun-centered coordinates, predicting that the perturber responsible for the observed disturbances is between –50 l –10. We explicitly show that the phase of the disturbances in the outskirts of simulated galaxies, our primary metric for the azimuth determination, is relatively insensitive to the equation of state (for the range of gas fractions of local spirals). Our calculations here represent our continuing efforts to develop the "tidal analysis" method of Chakrabarti & Blitz (CB09). CB09 employed SPH simulations to examine tidal interactions between perturbing dark sub-halos and the Milky Way. They found that the amplitudes of the Fourier modes of the observed planar disturbances are best fit by a perturbing dark sub-halo with mass ~one-hundredth that of the Milky Way, and a pericentric approach distance of ~5-10 kpc. The overarching goal of this work is to attempt to outline an alternate procedure to optical studies for characterizing and potentially discovering dwarf galaxies—whereby one can approximately infer the azimuthal location of a perturber, its mass, and pericentric distance (CB09) from analysis of its tidal gravitational imprints on the H I disk of the primary galaxy.
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.
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.
116898833
Spectral energy distributions of embedded protostars and dusty galaxies
16317166
Far-Infrared Spectral Energy Distributions and Photometric Redshifts of Dusty Galaxies
We infer the large-scale source parameters of dusty galaxies from their observed spectral energy distributions (SEDs) using the analytic radiative transfer methodology presented by Chakrabarti and McKee. For local ultraluminous infrared galaxies (ULIRGs), we show that the millimeter to far-infrared (FIR) SEDs can be well fit using the standard dust opacity index of 2 when self-consistent radiative transfer solutions are employed, indicating that the cold dust in local ULIRGs can be described by a single-grain model. We develop a method for determining photometric redshifts of ULIRGs and submillimeter galaxies from the millimeter-FIR SED; the resulting value of 1 + z is typically accurate to about 10% . As such, it is comparable to the accuracy of near-IR photometric redshifts and provides a complementary means of deriving redshifts from far-IR data, such as those from the upcoming Herschel Space Observatory. Since our analytic radiative transfer solution is developed for homogeneous, spherically symmetric, centrally heated, dusty sources, it is relevant for infrared bright galaxies that are primarily powered by compact sources of luminosity that are embedded in a dusty envelope. We discuss how deviations from spherical symmetry may affect the applicability of our solution, and we contrast our self-consistent analytic solution with standard approximations to demonstrate the main differences.
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
118514124
Cosmology of Hořava–Lifshitz f(R) gravity
Abstract We discuss the cosmology of recently proposed Hořava–Lifshitz f ( R ) gravity. In particular, we derive the modified Hubble equation that reduces to the standard HL gravity case in appropriate limit. We show how the bounce solutions in this theory are modified due to nonlinear effect of f ( R ) gravity. We also show that in principle, the Universe in this set-up can show cyclic behavior.
474602
Universal near-horizon conformal structure and black hole entropy
It is shown that a massless scalar probe reveals a universal near-horizon conformal structure for a wide class of black holes, including the BTZ. The central charge of the corresponding Virasoro algebra contains information about the black hole. With a suitable quantization condition on the central charge, the CFT associated with the black hole in our approach is consistent with the recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT framework has been identified with the construction of Frenkel, Lepowsky and Meurman. This CFT admits the Fischer–Griess monster group as its symmetry. The logarithm of the dimension of a specific representation of the monster group has been identified by Witten as the entropy of the BTZ black hole. Our algebraic approach shows that a wide class of black holes share the same near-horizon conformal structure as that for the BTZ. With a suitable quantization condition, the CFT's for all these black holes in our formalism can be identified with the FLM model, although not through the AdS/CFT correspondence. The corresponding entropy for the BTZ provides a lower bound for the entropy of this entire class of black holes.
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.
124097243
GRAVITATIONAL WAVE DAMPING FROM A SELF GRAVITATING VIBRATING RING OF MATTER AROUND A BLACK HOLE
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).