118984787
A NEW PROBE OF THE DISTRIBUTION OF DARK MATTER IN GALAXIES
The scale radius of dark matter halos is a critical parameter for specifying the density distribution of dark matter, and is therefore a fundamental parameter for modeling galaxies. We develop here a novel, observationally motivated probe to quantitatively infer its value within the context of the Navarro, Frenk, & White profile. We demonstrate that disturbances in the extended atomic hydrogen gas disks of galaxies can be analyzed to infer the scale radius of the dark matter halo. Our primary metric is the phase (i.e., the shape of the spiral) of the m = 1 mode of the disturbance in the outskirts of the gas disk, which we take to be produced by a tidal interaction. We apply the method to the Whirlpool galaxy, which has an optically visible satellite. We infer a scale radius of ~17 kpc for M51, which is consistent with expectations from dissipationless cosmological simulations. We explore potential degeneracies due to orbital inclination, initial conditions, satellite mass, and pericenter approach distance, and find our results to be relatively insensitive to these considerations. Our method of tracing the dark potential well through observed disturbances in outer gas disks is complementary to gravitational lensing.
17384070
The Role of Gas In Maintaining Quasi-Steady Spiral Structure In Stellar Disks
We study the dynamical evolution of spiral structure in the s tellar disks of isolated galaxies using high resolution Smoothed Particle Hydrodynamics (SP H) 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 com ponent. We find that angular momentum transport from the gas to the stars inside of corotati on 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 gase ou 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 e mploy 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 re lation. 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.
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.
124097243
GRAVITATIONAL WAVE DAMPING FROM A SELF GRAVITATING VIBRATING RING OF MATTER AROUND A BLACK HOLE
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.
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.
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.
10835186
A comparative study of Dirac quasinormal modes of charged black holes in higher dimensions
In this work we study the Dirac quasinormal modes of higher dimensional charged black holes. Higher dimensional Reissner–Nordström type black holes as well as charged black holes in Einstein–Gauss–Bonnet theories are studied for fermionic perturbations using WKB method. A comparative study of the quasinormal modes in the two different theories of gravity has been performed. The behavior of the frequencies with the variation of black hole parameters as well as with the variation of space-time dimensions is studied. We also study the large multipole number limit of the black hole potential in order to look for an analytic expression for the frequencies.