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
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.
119048179
Feedback-Driven Evolution of the Far-Infrared Spectral Energy Distributions of Luminous and Ultraluminous Infrared Galaxies
We calculate infrared spectral energy distributions (SEDs) from simulations of major galaxy mergers, and study the effect of active galactic nucleus (AGN) and starburst-driven feedback on the evolution of the SED as a function of time. We use a self-consistent three-dimensional radiative equilibrium code to calculate the emergent SEDs and to make images. To facilitate a simple description of our findings, we describe our results in reference to an approximate analytic solution for the far-IR SED. We focus mainly on the luminous infrared galaxy (LIRG) and ultraluminous infrared galaxy (ULIRG) phases of evolution. We contrast the SEDs of simulations performed with AGN feedback to simulations performed with starburst-driven wind feedback. We find that the feedback processes critically determine the evolution of the SED. Changing the source of illumination (whether stellar or AGN) has virtually no impact on the reprocessed far-infrared SED. We find that AGN feedback is particularly effective at dispersing gas and rapidly injecting energy into the ISM. The observational signature of such powerful feedback is a warm SED. In general, simulations performed with starburst-driven winds have colder spectra and reprocess more of their emission into the infrared, resulting in higher infrared to bolometric luminosities compared to (otherwise equivalent) simulations performed with AGN feedback. We depict our results in IRAS, as well as in Spitzer's MIPS bands, and in Herschel's PACS bands.
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.
119261143
Spikes in the SED and ripples in the outskirts of galaxies
We describe a new method that allows us to quantitatively characterize galactic satellites from analysis of disturbances in outer gas disks, without requiring knowledge of their optical light. We have demonstrated the validity of this method, which we call Tidal Analysis, by applying it to local spirals with known optical companions, including M51 and NGC 1512. These galaxies span the range from having a 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 as a decipher of the dynamical impact of satellites on galactic disks. Here, we present some preliminary results on the emergent SEDs and images, calculated along the time sequence of these dynamical simulations using the 3-D self-consistent Monte Carlo radiative transfer code RADISHE. We explore star formation prescriptions and how they affect the emergent SEDs and images. Our goal is to identify SED colors that are primarily affected by the galaxy's interaction history, and are not significantly affected by the choice of star formation prescription. If successful, we may be able to utilize the emergent UV-IR SED of the primary galaxy to understand its recent interaction history.
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.
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.
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.
42578428
Floating and sinking: the imprint of massive scalars around rotating black holes.
We study the coupling of massive scalar fields to matter in orbit around rotating black holes. It is generally expected that orbiting bodies will lose energy in gravitational waves, slowly inspiraling into the black hole. Instead, we show that the coupling of the field to matter leads to a surprising effect: because of superradiance, matter can hover into "floating orbits" for which the net gravitational energy loss at infinity is entirely provided by the black hole's rotational energy. Orbiting bodies remain floating until they extract sufficient angular momentum from the black hole, or until perturbations or nonlinear effects disrupt the orbit. For slowly rotating and nonrotating black holes floating orbits are unlikely to exist, but resonances at orbital frequencies corresponding to quasibound states of the scalar field can speed up the inspiral, so that the orbiting body sinks. These effects could be a smoking gun of deviations from general relativity.
118544491
Proof of universality of electrical conductivity at finite chemical potential
It was proposed in [1] that, for certain gauge theories with gravity duals, electrical conductivity at finite chemical potential is universal. Here we provide a general proof that, when matter stress tensor satisfies a compact constraint, electrical conductivity is universal. We further elaborate our result with several conformal as well as non-conformal gauge theories. We also discuss how boundary conductivity and universal conductivity of stretched horizon are related.
119181389
A new approach to modified gravity models
We investigate f (R)-gravity models performing the ADM-slicing of standard General Relativity. We extract the static, spherically-symmetric vacuum solutions in the general case, which correspond to either Schwarzschild de-Sitter or Schwarzschild anti-de-Sitter ones. Additionally, we study the cosmological evolution of a homogeneous and isotropic universe, which is governed by an algebraic and not a differential equation. We show that the universe admits solutions corresponding to acceleration at late cosmological epochs, without the need of fine-tuning the model-parameters or the initial conditions.