bluuebunny/crossref_metadata_2025 huggingface dataset:
Alternatives to Dark Matter (?)
Authors: Aguirre Anthony
Published: July 2016

It has long been known that Newtonian dynamics applied to the visible matter in galaxies and clusters does not correctly describe the dynamics of those systems. While this is generally taken as evidence for dark matter it is in principle possible that instead Newtonian dynamics (and with it General Relativity) breaks down in these systems. Indeed there have been a number of proposals as to how standard gravitational dynamics might be modified so as to correctly explain galactic dynamics without dark matter. I will review this general idea (but focus on “MOdified Newtonian Dynamics”, or “MOND”), and discuss a number of ways alternatives to dark matter can be tested and, in many cases, ruled out.
CDM in LSB Galaxies: Toward the Optimal Halo Profile
Authors: de Blok W. J. G
Published: July 2016

Low Surface Brightness (LSB) galaxies are dominated by dark matter. High-resolution rotation curves suggest that their total mass-density distributions are dominated by constant density cores rather than the steep and cuspy distributions found in Cold Dark Matter (CDM) simulations. the data are best described by a model with a soft core with an inner power-law mass-density slope α = 0.2 ± 0.2. However no single universal halo profile provides an adequate description of the data. the observed mass profiles appear to be inconsistent with ACDM.
Small-scale Substructure in Dark Matter Haloes: Where Does Galaxy Formation Come to an End?
Authors: Taylor J. E. , Silk J. , Babul A.
Published: July 2016

Models of structure formation based on cold dark matter predict that most of the small dark matter haloes that first formed at high redshift would have merged into larger systems by the present epoch. Substructure in present-day haloes preserves the remains of these ancient systems, providing the only direct information we may ever have about the low-mass end of the power spectrum. We describe some recent attempts to model halo substructure down to very small masses, using a semi-analytic model of halo formation. We make a preliminary comparison between the model predictions, observations of substructure in lensed systems, and the properties of local satellite galaxies.
The EROS2 Microlensing Study of the Galaxy
Authors: Hamadache Clarisse
Published: July 2016

The latest results of the Eros2 experiment are presented. the search for gravitational microlensing events toward the Galactic Center and toward the Magellanic Clouds yielded an optical depth τbulge = 0.94 ± 0.29 × 10–6, and a strong limit, combining all Eros analyses, on the composition of the halo. Less than 25% of a standard halo can be composed of MACHOs with a mass range [10–7, 1] M⊙ at the 95% C.L.
Direct Mapping of Massive Compact Objects in Extragalactic Dark Halos
Authors: Inoue Kaiki Taro , Chiba Masashi
Published: July 2016

We propose a method for directly detecting MASsive Compact Objects (MASCOs) in extragalactic halos, using VLBI techniques with extremely high resolution ˜ 0.01 milli-arcsec. If a galactic halo comprising a large number of MASCOs produces multiple images of a background radio-loud QSO by gravitational lensing, then a high-resolution radio map of each macro-lensed image should reveal microlensing effects by MASCOs. Based on the size, position, and magnified or demagnified patterns of images, we shall be able to determine the mass and density profile of an individual MASCO as well as its spatial distribution and abundance in a galactic halo.
Mass-to-Light Ratios of Early- and Late-Type Galaxies
Authors: Brainerd Tereasa G. , Specian Michael A.
Published: July 2016

Using the 100k data release of the 2dF Galaxy Redshift Survey (2dFGRS), we obtain mass-to-light ratios for isolated “host” galaxies via the dynamics of satellite galaxies which orbit about them. Distinct differences are seen in the dependence of M/L on host luminosity for early-type vs. late-type hosts.
Elliptical Galaxies: Darkly Cloaked or Scantily Clad?
Authors: Romanowsky A. J. , Douglas N. G. , Kuijken K. , Merrifield M. R. , Arnaboldi M. , Napolitano N. R. , Merrett H. , Capaccioli M. , Freeman K. C. , Gerhard O.
Published: July 2016

Planetary nebulae (PNe) may be the most promising tracers in the halos of early-type galaxies. We have used multi-object spectrographs on the WHT and the VLT, and the new Planetary Nebula Spectrograph on the WHT, to obtain hundreds of PN velocities in a small sample of nearby galaxies. These ellipticals show weak halo rotation, which may be consistent with ab initio models of galaxy formation, but not with more detailed major merger simulations. the galaxies near L* show evidence of a universal declining velocity dispersion profile, and dynamical models indicate the presence of little dark matter within 5 Reff—implying halos either not as massive or not as centrally concentrated as CDM predicts.
Search for cool white dwarfs with GSC2
Authors: Carollo D. , Spagna A. , Lattanzi M.G. , Smart R.L. , Hodgkin S.T. , Terranegra L. , Mclean B.
Published: July 2016

Microlensing experiments have suggested that a significant part of the dark halo of the Milky Way could be composed of matter in the form of massive compact halo objects (MACHOs). Cool ancient white dwarfs (WDs) are the natural candidates. Here we present a new survey of halo WDs and evaluate the local space density using an accurate kinematic analysis. A comparison to a revaluation of the Oppenheimer et al. result is also provided. the local space density estimated for the two independent samples is about ~ 10–5M⊙ pc–3.
Mass of the Milky Way
Authors: Wong O. I. , Drinkwater M. J. , Jones J. B. , Gregg M. D. , Freeman K. C.
Published: July 2016

We present a new estimate of the mass of the Milky Way based on the escape velocity of a sample of distant stars, about 12 kpc from the Galactic centre and about 5 kpc from the plane of the Galaxy. Our sample is very different from previous escape-velocity studies, being compiled from an all-object spectroscopic survey of a region of sky. the derived mass within 12 kpc of the Galactic centre is (1.3 ±0.3) × 1011M⊙.
The dark matter density problem in massive disk galaxies
Authors: Weiner Benjamin J.
Published: July 2016

We discuss measurements of disk mass from non-circular streaming motions of gas in the barred galaxies NGC 3095 and NGC 4123. in these galaxies with strong shocks and non-circular motions, the inner regions must be disk-dominated to reproduce the shocks. This requires dark matter halos of low central density and low concentration, compared to LCDM halo predictions. in addition, the baryonic collapse to a disk should have compressed the halo and increased the dark matter density, which sharpens the disagreement. One possible resolution is a substantial amount of angular momentum transfer from disk to halo, but this is not particularly attractive nor elegant.
Fast bars in SBO galaxies
Authors: Corsini Enrico Maria , L. Aguerri J. A. , Debattista Victor P.
Published: July 2016

We measured the bar pattern speed in a sample of 7 SB0 galaxies using the Tremaine-Weinberg method. This represents the largest sample of galaxies for which the bar pattern speed has been measured this way. All the observed bars are as rapidly rotating as they can be. We compared this result with recent high-resolution N-body simulations of bars in cosmologically-motivated dark matter halos, and conclude that these bars are not located inside centrally concentrated halos.
Boxy isophotes in face–on views of barred galaxies
Authors: Patsis Panos A. , Skokos Charalampos , Athanassoula E.
Published: July 2016

We study the conditions that favour boxiness of isodensities in the face-on views of orbital 3D models for barred galaxies. in particular, we consider several cases with different mass values for the bar, disk and bulge components of the potential, as well as different values of the bar pattern speed. Using orbital weighted profiles of the basic stable periodic orbits of the x1 tree for every model, we show that boxiness is in general a composite effect due to the presence of stable orbits belonging to several 2D and 3D families.
Properties of Dark Matter Halos in Disk Galaxies
Authors: de Jong Roelof S. , Kassin Susan , Bell Eric F. , Courteau Stéphane
Published: July 2016

We present a simple technique to estimate mass-to-light (M/L) ratios of stellar populations based on two broadband photometry measurements, i.e. a colour-M/L relation. We apply the colour-M/L relation to galaxy rotation curves, using a large set of galaxies that span a great range in Hubble type, luminosity and scale size and that have accurately measured HI and/or Hα rotation curves. Using the colour-M/L relation, we construct stellar mass models of the galaxies and derive the dark matter contribution to the rotation curves.

We compare our dark matter rotation curves with adiabatically contracted Navarro, Frenk, & White (1997, NFW hereafter) dark matter halos. We find that before adiabatic contraction most high surface brightness galaxies and some low surface brightness galaxies are well fit by a NFW dark matter profile. However, after adiabatic contraction, most galaxies are poorly fit in the central few kpc. the observed angular momentum distribution in the baryonic component is poorly matched by ACDM model predictions, indicating that the angular momentum distribution is not conserved during the galaxy assembly process. We find that in most galaxies the dark matter distribution can be derived by scaling up the HI gas contribution. However, we find no consistent value for the scaling factor among all the galaxies.
Dynamical Modeling using Evolutionary Algorithms
Authors: Mathieu Anne
Published: July 2016

I will present a new method of dynamical modeling of stellar systems based on evolutionary algorithms. the technique will be illustrated with an application to the problem of recovering the gravitational potential of a thin galactic disc from kinematic observables in a non-parametric way.
A 3D Optical Spectroscopy Study of Low Surface Brightness Galaxies
Authors: Chemin L. , Amram P. , Carignan C. , Balkowski C. , van Driel W. , Cayatte V. , Hernandez O. , Boulesteix J. , Marcelin M.
Published: July 2016

We present Hα emission line velocity fields of two Low Surface Brightness galaxies (LSBs) - UGC 628 and UGC 5005 - obtained using Fabry-Perot (FP) interferometry observations at the Canada-France-Hawaii telescope. Our goal is to study the dynamics of LSBs.
Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies
Authors: Kormendy John , Freeman K. C.
Published: July 2016

Published mass models fitted to galaxy rotation curves are used to study the systematic properties of dark matter (DM) halos in late-type and dwarf spheroidal (dSph) galaxies. Halo parameters are derived by fitting non-singular isothermals to (V2 – V2vis)1/2, where V(r) is the observed rotation curve and Vvis is the rotation curve of the visible matter. the latter is calculated from the surface brightness assuming that the mass-to-light ratio M/L is constant with radius. “Maximum disk” values of M/L are adjusted to fit as much of the inner rotation curve as possible without making the halo have a hollow core. Rotation curve decomposition becomes impossible fainter than absolute magnitude Mb ≃ −14, where V becomes comparable to the velocity dispersion of the gas. To increase the luminosity range further, we include dSph galaxies, which are physically related to spiral and irregular galaxies. Combining the data, we find that DM halos satisfy well defined scaling laws analogous to the “fundamental plane” relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii rc, higher central densities ρ0, and smaller central velocity dispersions σ. Scaling laws provide new and detailed constraints on the nature of DM and on galaxy formation and evolution. Some simple implications include:

1 – A single, continuous physical sequence of increasing mass extends from dSph galaxies with Mb ≃ −7.6 to Sc I galaxies with Mb ≃ −22.4.

2 – the high DM densities in dSph galaxies are normal for such tiny galaxies. Since virialised density depends on collapse redshift zcoll, ρ0 ∝ (1 + zcoll)3, the smallest dwarfs formed at least Δzcoll ≃ 7 earlier than the biggest spirals.

3 – the high DM densities of dSphs implies that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. Tidal dwarfs cannot retain even the low DM densities of their giant-galaxy progenitors. in contrast, dSphs have higher DM densities than do giant-galaxy progenitors.

4 – the fact that, as luminosity decreases, dwarf galaxies become much more numerous and also more nearly dominated by DM raises the possibility that there exists a large population of objects that are completely dark. Such objects are a canonical prediction of cold DM theory. If they exist, “empty halos” are likely to be small and dense -that is, darker versions of Draco and UMi.

5 – the slopes of the DM parameter correlations provide a measure on galactic mass scales of the slope n of the power spectrum |δk|2 ∝ kn of primordial density fluctuations. Our preliminary results, not yet corrected for baryonic compression of DM, give n ≃ –1.9 ± 0.2. This is consistent with cold DM theory.
The shapes of simulated dark matter halos
Authors: Springel Volker , White Simon D. M. , Hernquist Lars
Published: July 2016

Dark matter halos formed in CDM simulations are known to have triaxial shapes, with substantial distortions from spherical symmetry. However, conflicting claims have been made with respect to radial variations of halo shape, or trends with mass. We propose a new, more robust method to determine halo shapes based on the gravitational potential, thereby avoiding measurement uncertainties that may be the cause of these discrepancies. We find a strong preference towards prolate halo shapes, with mean minor-to-major axis-ratios close to ~ 0.5. Spherical halos are generally very rare, but there is a trend for smaller mass systems to be less elongated. We also compare dark halo shapes found in hydrodynamical simulations that include radiative cooling, star formation, and feedback processes, with those measured in equivalent collisionless simulations. Dissipation makes dark halos substantially rounder at small radii, to the extent that their shape distribution matches that of elliptical galaxies.
WIMP direct detection and halo structure
Authors: Green Anne M.
Published: July 2016

Weakly Interacting Massive Particle (WIMP) direct detection experiments are just reaching the sensitivity required to detect Galactic dark matter in the form of neutralinos (or indeed any stable weakly interacting particle). Detection strategies and data analyses are often based on the simplifying assumption of a standard spherical, isothermal halo model, but observations and numerical simulations indicate that galaxy halos are in fact triaxial and anisotropic, and contain substructure. the annual modulation and direction dependence of the event rate (due to the motion of the Earth) provide the best prospects of distinguishing WIMP scattering from background events, however these signals depend sensitively on the local WIMP velocity distribution. I briefly review the status of WIMP direct detection experiments before discussing the dependence of the annual modulation signal on astrophysical input, in particular the structure of the Milky Way halo, and the possibility that the local WIMP distribution is not smooth.
CRESST Detectors for Nonbaryonic Cold Dark Matter Particles
Authors: Jagemann Thomas
Published: July 2016

The CRESST experiment is set up for the direct detection of Weakly Interacting Massive Particles (WIMPs) which our Galactic dark matter halo possibly consists of. the employed detection method is elastic scattering by nuclei. the recoiling nucleus deposits most of its energy in the form of lattice vibrations in the detector. Cooling the detector to very low temperatures (mK) enhances the temperature rise due to the energy deposition. the crucial parameter for direct WIMP searches is the sensitivity to the WIMP interaction cross section in a certain range of possible WIMP masses. CRESST is now sensitive enough to explore the parameter space predicted by supersymmetric models.
Solar Coronal Mass Ejections
Authors: Hundhausen A. J. , Sime D. G. , Low B. C.
Published: July 2016

In addition to the more or less steady solar wind, the Sun also ejects mass in highly time dependent events taking place in the corona once every few days at solar activity minimum and as often as three times a day at solar activity maximum (Hundhausen 1988, Low 1986). These events involve large scale reconfiguration of the corona with an expulsion of some 1015g of ionized material into interplanetary space. The High Altitude Observatory (HAO) operates a groundbased internally occulted coronagraph at Mauna Loa, Hawaii, with a field of view of the corona from 1.2 to 2.2R⊙ in heliocentric distance, registering polarization brightness. A second instrument at the same site in Hawaii observes the solar limb in Hα emission to detect chromospheric material from the limb out to 1.5R⊙. HAO also operates an externally occulted coronagraph/polarimeter onboard the NASA Solar Maximum Mission Satellite (SMM) launched in 1980, capitalizing on the advantage of space with a field of view from 1.5 to 6R⊙ to cover the fainter outer corona. Coronal mass ejections involve magnetic field reconfiguration from high in the corona down to the base lying below 1.1R⊙. Important physical insights can be had when simultaneous observations by HAO's three instruments are put together with a common scale and orientation to reveal a mass ejection in the full extent of the solar atmosphere from the limb outward. Combined observations of two mass ejections are presented, one associated with an eruptive prominence and the the other associated with a flare. The significance of these two events is that in both cases, the mass ejection was in fully developed motion and had traveled high into the corona well before the onset of the associated prominence or flare eruption, pointing to an instability in the large scale coronal magnetic field as the underlying cause of the global reconfiguration.
The Magnetic Field of the Milky Way
Authors: Trimble Virginia
Published: July 2016

Since its discovery 40 years ago as a confiner of cosmic rays and an aligner of interstellar dust grains, the Galactic magnetic field has been studied through emission and polarization of synchrotron radiation, Faraday rotation, Zeeman splitting, and effects on gas flows and morphology. The local field has a coherent, few microgauss, component roughly along the local spiral arm and a comparable chaotic component. Field direction in the plane is reversed one or more times both inside and outside the solar circle. Loops and spurs extend outside the plane and may merge with a general dipole, which is most conspicuous near the Galactic center. There may be a separate thick disc magneto-ionic component. Comparison with other galaxies, especially grand design vs. flocculent spirals should eventually prove fruitful. Parameters are not currently well enough known to rule out dipole or primordial origin.
The Alpha-Effect in Galaxies is Highly Anisotropic
Authors: Rüdiger G.
Published: July 2016

Besides the mean flow the alpha is the other input quantity for any mean-field dynamo model. It describes the generation of turbulent electromotive force  from a large-scale field  for a given turbulence. The necessary helicity of the turbulence results from the joint action of Coriolis force and density stratification. The standard estimate of 1 km/s for alpha in galaxies is a surely well-established approximation. One of the essentials, however, remains open. Due to the extremely anisotropic structure of disks the tensorial character of alpha can no longer be ignored. In stellar applications anisotropy in the α-tensor leads to a preferred excitation of non-axisymmetric magnetic fields. That is true for α2 -dynamos if the alpha parallel to the rotation axis, α||, is much smaller than that in the equatorial plane, α⊥. The idea is that also for disk-like configurations a similar behaviour makes the existence of the observed large-scale non-axisymmetric magnetic BSS modes understandable within the frame of the mean-field dynamo theory.
Dynamo Generation of Galactic Magnetic Fields
Authors: Donner Karl Johan
Published: July 2016

I give some results of calculations of the magnetic fields generated by dynamo processes in galaxy models consisting of a turbulent disc embedded in a low-conductivity halo. The field configuration is found to be strongly dependent on the turbulent structure of the disc.
3–D Models of Galaxy Magnetic Fields with Spiral Shocks
Authors: Panesar J. , Nelson A.H.
Published: July 2016

We report here some preliminary results of 3–D numerical simulations of an α–ω dynamo in galaxies with differential rotation, small–scale turbulence, and a shock wave induced by a stellar density wave. We obtain the magnetic field from the standard dynamo equation, but include the spiral shock velocity field from a hydrodynamic simulation of the gas flow in a gravitational field with a spiral perturbation (Johns and Nelson, 1986).
3-Dimensional Particle-in-Cell Simulations of Spiral Galaxies
Authors: Peratt A. L. , Peter W. , Snell C. M.
Published: July 2016

The advent of 3-dimensional, electromagnetic, and fully relativistic particle simulations allows a detailed study of a magnetized plasma galaxy model. When two such models are simulated, an interaction yielding results resembling observational data from double radio sources, including the emission of synchrotron radiation, are obtained. Simulation derived morphologies, radiation intensities, frequency spectra and isophote patterns are produced by the model which can be directly compared to observational data. Long time simulation runs (~109 years) show the evolution of barred spiral galaxies with large scale bisymmetric magnetic field distributions having 100μG field strengths.
Diamagnetic Cavities in the Interstellar Medium
Authors: Gisler Galen
Published: July 2016

Violent events such as supernova explosions or gradual processes such as mass loss from hot supergiant stars produce diamagnetic cavities: the interstellar magnetic field, frozen into ambient plasma, is excluded from a region around the source of expanding injected plasma. Particle-in-cell simulations illustrate the formation of such diamagnetic cavities in both the steady and impulsive cases. Plasma loss along the field means that the cavity always tends toward a cylindrical or barrel shape, even for very weak magnetic fields. Ion acceleration is expected out the ends of the barrel for all parameters of injection and initial field.
Interaction of Cosmic Rays with a Galactic Corona Bow-Shock
Authors: Ostrowski M.
Published: July 2016

Basing on a simple 1-dim model, the process of diffusive particle acceleration at a galactic bow-shock is discussed.
The Detailed Magnetic Field Structure in the SW Quadrant of M31
Authors: Beck R. , Berkhuijsen E.M.
Published: July 2016

A three-dimensional, arc-like structure in the magnetic field was found coming out of the plane of M31. This structure may be the first Parker-Jeans instability observed in an external galaxy.
What Mechanism Depolarizes the Emission from the SW Arm of M31?
Authors: Berkhuijsen E.M. , Beck R.
Published: July 2016

Gradients in rotation measure and dispersion in rotation measure, both across the telescope beam, depolarize the radio emission from the SW arm of M31. Faraday effects along the line of sight appear to be negligible.
Polarized Radio Emission from NGC 6946
Authors: Beck R. , Buczilowski U.R. , Harnett J.I.
Published: July 2016

New VLA radio observations of NGC 6946 reveal a complicated structure of the magnetic field with possibly radial changes in the foreground Faraday rotation, the strength of the uniform field and the particular dynamo mode in operation. The uniform field is strongest in the interarm regions, but shows no deducible large-scale structure in the radius range of the optical spiral arms. The high star formation rate in NGC 6946 apparently increases the turbulence of the interstellar magnetic field.
Optical Polarization of M 82
Authors: Neininger N. , Beck R. , Backes F.
Published: July 2016

We observed a sample of nearby galaxies using the CCD-Polarimeter of the Landessternwarte Heidelberg in the R-Band with the 1.23-m telescope of the MPIA at Calar Alto. In most cases polarization was found but the polarization structures cannot be easily related to a single phenomenon. If there is a strong point source, Rayleigh scattering leads to circular patterns of the polarization vectors. If dust grains are aligned in a magnetic field, this so-called Davis-Greenstein-mechanism gives more uniformly distributed E-vectors, which can be distinguished from the Rayleigh scattering. The example of M 82 given here shows both kinds of polarized light. There is evidence of a strong magnetic field component perpendicular to the disk which seems to have its origin in the center of the galaxy. This is consistent with theoretical models as well as with previous observations.
Magnetic Field Structure in the Small Magellanic Cloud
Authors: Magalhães A.M. , Loiseau N. , Rodrigues C.V. , Piirola V.
Published: July 2016

The present status of an ongoing observational program to study the magnetic field structure of the SMC by means of optical polarimetry is presented. Being the SMC more distant than the LMC, the observed optical polarization would mainly originate in the distorted outer layers in the front side of the SMC. Highly sensitive data obtained up to now show a magnetic field aligned with the HI bridge connecting the SMC with the LMC, revealing one of the few detected intergalactic magnetic fields associated with interacting galaxies.
Stochastic Star Formation and Magnetic Fields
Authors: Feitzinger J. V. , Harfst E. , Spicker J.
Published: July 2016

The model of selfpropagating star formation uses local processes (200 pc cell size) in the interstellar medium to simulate the large scale cooperative behaviour of spiral structure in galaxies. The dynamic of the model galaxies is taken into account via the mass distribution and the resulting rotation curve; flat rotation curves are used. The interstellar medium is treated as a multiphase medium with appropriate cooling times and density history. The phases are: molecular gas, cool HI gas, warm intercloud and HII gas and hot coronal fountain gas. A detailed gas reshuffeling between the star forming cells in the plane and outside the galactic plane controls the cell content. Two processes working stochastically are incooperated: the building and the decay of molecular clouds and the star forming events in the molecular clouds.
Magnetic Fields in Molecular Clouds at High Galactic Latitudes
Authors: Seki Munezo
Published: July 2016

We have detected interstellar polarization amounting to 2.6 % in the Ursa Major molecular clouds at a distance of 110 pc. Assuming that paramagnetic grains in those clouds are aligned with the magnetic fields and combining our results with the measurement of Zeeman splitting at 21 cm (Heiles 1989), we argue the strength and direction of magnetic fields.
Magnetic Fields and Star Formation: Imaging Polarimetry of Two Reflection Nebulae
Authors: Scarrott S.M. , Gledhill T.M.
Published: July 2016

Imaging polarimetry has shown that extended objects within star forming clouds may appear polarised due to passage of the light through an intervening region of magnetically aligned dust grains. Two such objects are considered here.
Numerical Models of Magnetic Disk Accretion in Star Forming Regions
Authors: Norman Michael L. , Stone James M.
Published: July 2016

We report on preliminary numerical MHD simulations of magnetic disk accretion surrounding a compact protostar in which the disk and the hydromagnetic wind interact self-consistently. We show that an outflow is indeed produced, but that its properties are sensitive to the assumed initial poloidal magnetic field structure. In particular, we reconcile the apparently disparate models of Pudritz and Norman (1983,1986) and Uchida and Shibata (1985) concerning the mass ejection mechanism.
Random Precessing Jet and Accretion Disk at the Galactic Center
Authors: Fujimoto M. , Sofue Y.
Published: July 2016

As a mechanism to generate asymmetric radio features in the central 50 pc of the Galaxy (Sofue and Fujimoto 1987), we consider a gaseous jet from the tilted accretion disk at the center and the interaction of the jet with ambient gas on the galactic plane. It is shown schematically in figure 1 that the magnetic torques N1,2,3 exert on a gaseous element ρhΔsΔr of a ring to change its tilted orbital plane,

and

where γ1,2,3 are constants of a factor of unity and e1,2,3 unit vectors. The azimuthal angle ϕ is measured along the rotation from the lowest part of the ring below the galactic plane. The orbital plane is tilted against the galactic plane by the angle θ The change of the angular momentum of the disk element L = ρhΔsΔrr × v is,

where 〈〉 means the average over one rotation period T or over ϕ = 0 to 2π in equations (1) to (3).
OH Zeeman Determination of the Magnetic Field at the Galactic Centre
Authors: Killeen N.E.B. , Lo K. Y. , Sault R. J. , Crutcher R. M.
Published: July 2016

Mid and far IR measurements of polarized dust continuum emission from within the central 5 pc of the Galaxy have been cited as evidence for magnetic alignment of dust grains. Indirect arguments have been used to infer a B-field strength of ~ 10 mG. The presence of such high B-field would play a significant role in the hydrodynamics of the ionized and neutral gas within the region. To obtain a direct measurement of the line-of-sight B-field strength, we conducted VLA observations to try and detect the Zeeman splitting in the 1667 MHz OH absorption line against the SgrA radio source. We observed with A/B configuration, 256 1.1 km s−1 channels, and 3 arcsec resolution. In addition, both left and right circular polarizations were acquired simultaneously. We used the maximum likelihood statistical analysis technique for low signal-to-noise ratio Zeeman data discussed by Sault, Killeen, Loushin, and Zmuidzinas (1989). Analysis of the resulting absorption line spectra is complicated by the many foreground clouds. Excluding the foreground clouds by judicious selection of spectral windows, the strongest absorption by the molecular material closest (in projection) to SgrA∗ is in what Güsten et al. (1987) refer to as the redshifted cloud (it does not appear to be partaking in the general rotation of the circum-nuclear disk but is thought to be in the local vicinity of SgrA∗). Preliminary analysis reveals no detections, and 3-σ upper limits to the line-of-sight magnetic field throughout the red-shifted cloud of approximately 4 mG. By careful simulation of the lines (Gaussians are quite good approximations to these broad [40 km s−1] lines) in select spatial regions of the redshifted cloud, we find that a line-of-sight field as strong as 10 mG should be clearly detectable at about the 10-σ level if it is present. Our data do not show fields at this level.
Magnetic Fields in Radio-Quiet Quasars
Authors: Schlickeiser R. , Crusius-Wătzel A.
Published: July 2016

As an hypothesis the sharp far–infrared turnovers in the spectra of several radio–quiet galactic nuclei [1–3] are attributed to the modifications of synchrotron emission arising from the presence of a thermal background plasma. We calculate the synchrotron emission from a power-law distribution of relativistic electrons N(γ) = Noγ–s in a large–scale random magnetic field of strength B embedded in a thermal plasma of density ne. Two major modifications of the classical vacuum theory of synchrotron emission are established [4]:

A) synchrotron sources can be optically thick only in a small frequency range around the Razin -Tsytovich frequency, whereas at smaller and higher frequencies the sources are optically thin;

B) at frequencies above VR the synchrotron intensity in a plasma behaves exactly the same way as in the vacuum case, whereas at frequencies below VR the intensity is exponentially reduced,
An Overview of Computational MHD Jets and Their Comparisons with Recent High Resolution Radio Images
Authors: Clarke David A.
Published: July 2016

Significant progress has been made in comparing numerical simulations with radio images of astrophysical jets. One is no longer forced to compare density slices through an axisymmetric jet simulation with observed Stokes I images. With the advent of MHD codes and modern supercomputers, models can now be constrained by all four Stokes parameters. In this paper, recent efforts to simulate synchrotron emission images of extragalactic radio jets are reviewed.
Computational MHD Jets
Authors: Shibata Kazunari
Published: July 2016

By using two-dimensional magnetohydrodynamic (MHD) code, the following non-steady MHD jets and outflows are studied in relation to jets ejected from central regions of galaxies: (1) a jet driven by gas pressure gradient, collimated by vertical magnetic fields (as a model of bipolar flows ejected from a hot bubble created by starbursts); (2) a magnetic twist jet which is accelerated and collimated by J × B force in relaxing magnetic twists generated by the interaction of poloidal fields with a rotating disk (as a model of jets from active galactic nuclei); (3) a magnetic-loop-outflow resulting from the Parker instability, which may account for the initial acceleration of the magnetic twist jet and nonthermal emissions near nuclear accretion disks.
Numerical Observations of a Restarting Radio Jet
Authors: Clarke David A. , Burns Jack O. , Norman Michael L.
Published: July 2016

An MHD computation of a restarting jet is presented and compared with observations of classical double radio sources. Assuming ideal MHD and an adiabatic equation of state, it is found that a “partial” jet exists for about 25% of the time, and that the terminal hotspot dissipates quickly compared to other physical time scales once the outflow of the jet is terminated.
Oblique Shocks in Extragalactic Jets
Authors: Fraix-Burnet D.
Published: July 2016

In the framework of the diffusive shock acceleration of relativistic electrons in extragalactic jets, we show that it is possible to derive the speed of the jet. For this purpose, we transform continuity relations through an oblique shock front into the reference frame of the observer. We apply these calculations to knot A of the M87 jet. Measuring the deviation of the fluid through the shock front from high-resolution radio maps and the deviation of the magnetic field from optical polarization maps (Fraix-Burnet et al., 1989), we derive speeds of about 0.01 c (Fraix-Burnet and Biermann, in preparation). The compression ratio is most probably 4 and the magnetic field is nearly parallel to the shock front both upstream and downstream.
The Shock Structure in Current-Carrying Jets
Authors: Lesch H. , Appl S. , Camenzind M.
Published: July 2016

We exploite the detailed calculations and observations of the earth bow-shock and suggest that similar collective plasma processes can account for the dissipation in hot spots of extragalactic radiosources. On the base of magnetohydrodynamic models for the origin and propagation of current carrying jets we show that in the terminal shock in hot spots lower hybrid-turbulence is excited. This turbulence driven by drifting electrons in the shock provides the anomalous conductivity required for current closure. Lower-hybrid turbulence is also generated by ion reflection in the upstream plasma. The kinetic energy of these ion beams is partially transformed into lower hybrid wave energy. These waves also determine the ratio of energies taken for plasma heating and particle acceleration. This is due to the fact that lower hybrid waves propagate almost perpendicular to the magnetic fields (large (small) wavenumbers perpendicular (parallel) to the magnetic field), their phase velocity parallel to the B-field are much larger than perpendicular to the field. Therefore electrons and ions are differently coupled to these waves. The resonant interactions of the upstream plasma with these waves leads to strong ion heating and electron acceleration. The ions reach a temperature (Ti ≃ 51011K). The electrons are accelerated up to relativistic energies (γ ≃ 1300).
Peculiar Magnetic Field Structures in 4C49.22 (1150+497)
Authors: Akujor Chidi E.
Published: July 2016

We present radio polarisation observations of the quasar 4C49.22. It shows no evidence of depolarisation on the counter–jet side, while exhibiting strong variation of fractional polarisation along the jet, as well as transverse offset of maximum fractional polarisation from each knot in the jet.
Evidence of a Large Scale Magnetic Field in the Coma - A1367 Supercluster
Authors: Giovannini G. , Kim K.-T. , Kronberg P. P. , Venturi T.
Published: July 2016

The Coma cluster is a rich cluster of galaxies nested in an even larger supercluster of galaxies. The plane of the supercluster appears to be defined by the Coma cluster itself and another galaxy cluster, Abell 1367, that lies about 40 Mpc (H0 = 75 Mpc km−1s−1 (≡h75)) farther west (Tifft and Gregory 1976).
The Role of Extragalactic Jets in the Magnetization of the Intergalactic Medium
Authors: Jafelice L.C. , Opher R.
Published: July 2016

We consider a current carrying extragalactic jet and the corresponding return current closing the circuit. The Lorentz force for the return path is expansive. Assuming that the expansion occurs at the local Alfvén velocity, we calculate numerically the radial distance from the jet axis which the return circuit reaches due to this electrodynamic expansion. The calculations are made explicity for parameter values observed for the sources Cygnus A, NGC 6251, 3C465 and M84. The results obtained can explain several magnetic features observed in these sources. The possible importance of previous generations of extragalactic jets in the large scale magnetization of the intergalactic medium is also discussed.
Non-Conventional Origin of Large-Scale Magnetic Fields
Authors: Wanas M.I.
Published: July 2016

One of the models constructed (Wanas, 1985) within the framework of the generalized field theory (Mikhail and Wanas, 1977) is found to give results in favour of Blackett's speculation concerning rotation and the origin of magnetic fields. The formula giving the surface polar magnetic field of a spherical body of mass M, radius R, and uniform rotational velocity w is given by (Mikhail and Wanas, 1989)

In case of a typical galaxy, the model gives a magnetic field of the order of 10-5 Gauss.
The Shape of the Kα Line as the Evidence for the Black Hole Existence
Authors: Zakharov Alexander F. , Repin Serge V.
Published: July 2016

Observations of Seyfert galaxies in X-ray region reveal the wide emissive lines in their spectra, which can arise in inner parts of accretion disks, where the effects of General Relativity (GR) must be taken into account. A spectrum of a solitary emission line of a hot spot in Kerr accretion disk is simulated, depending on the radial coordinate r and the angular momentum a = J/M of a black hole, under the assumption of equatorial circular motion of a hot spot. It is shown that the characteristic two-peak line profile with the sharp edges arises at a large distance, (about r ≈ (3 − 10) rg). The inner regions emit the line, which is observed with one maximum and extremely wide red wing. We present results of simulations for the isothermal and Shakura – Sunayev disks.
Gravitational Lensing by Globular Clusters and Arp Objects
Authors: Yushchenko Alexander , Kim Chulhee , Sergeev Alexander , Niarchos Panos , Manimanis Vasilis
Published: July 2016

We try to explain quasar-galaxy associations by gravitational lensing by globular clusters, located in the halos of foreground galaxies. We propose observational test for verification of this hypothesis. We processed SUPERCOSMOS sky survey and found overdensities of star-like sources with zero proper motions in the vicinities of foreground galaxies from CfA3 catalog. We show mean effect for galaxies with different redshifts. Two effects can explain observational data - these are lensing by globular clusters and lensing by dwarf galaxies. We made CCD 3-color photometry with 2.0-1.2 meter telescopes to select extremely lensed objects around several galaxies for spectroscopic observations.
Does the Black Hole Rotation Lead to Higher X-Ray Variability in the Narrow-Line Objects?
Authors: Bian W. , Zhao Y.
Published: July 2016

This paper presents a analysis of X-ray variability for a assembled sample of broad-line Seyfert 1, narrow-lines Seyfert 1 galaxies and QSOs observed by ASCA, whose central black masses have been estimated. We find the significant relation between X-ray variability and the central black masses is different for Broad-line and Narrow-lines galaxies. The higher excess variance of narrow-line galaxies can be explained that they have smaller size of X-ray emission region compare to the broad-line objects. Our findings favor the hypothesis that the narrow-line galaxies have rotational black hole and hence maybe have the jets.
Beaming Effects in Gamma-Ray Burst Afterglows
Authors: Huang Y. F. , Lu T. , Dai Z. G. , Cheng K. S.
Published: July 2016

Based on a refined dynamical model, afterglows from jetted γ-ray burst (GRB) remnants are investigated numerically. Measuring of GRB beaming by using orphan afterglow surveys is addressed. The possible existence of a kind of cylindrical jets is also discussed.
GLAST and Gamma-Ray Bursts
Authors: Preece Robert D.
Published: July 2016

The two instruments aboard the Gamma-Ray Large Area Space Telescope (GLAST) mission will make unprecedented spectral observations of gamma-ray bursts. I will discuss what new science we can expect from GLAST.
A Calibration of FWHM vs. v for UV Lines
Authors: Ramírez Isidro , Koenigsberger Gloria , Kurucz Robert L.
Published: July 2016

The UV spectra predicted by LTE line-blanketed model atmosphere calculations are used to obtain a preliminary calibration of FWHM vs. v for UV lines, which is then used to determine the values of v sin i for four O-type stars in the Small Magellanic Cloud.
Fast Rotating Stars: Effect of the Aspect Angle on Line Profiles
Authors: Frémat Y. , Zorec J. , Hubert A. M. , Floquet M. , Leister N. , Levenhagen R. , Chauville J. , Ballereau D.
Published: July 2016

Fast rotation is expected to flatten the star and to produce non uniform temperature and density distributions (i.e. gravitational darkening). While the flattening mostly increases the absolute flux level of the energy distribution, gravitational darkening makes an equator-on star apparently cooler than a star seen through the pole. Both effects (Collins et al. 1991) influence the colours and the location of the star in the HR diagram but also, in a more subtle way, its spectral line profiles. More particularly, in early B type stars, gravitational darkening tends to privilege at the poles the formation of the ions with the highest ionization potentials and directly affects line formation. Consequently, most spectral line shapes - and especially the weakest ones - become aspect angle dependent which in several cases may play a role in the fundamental parameter determination procedures or even in the determination of stellar chemical abundances.
New Projected Rotational Velocities of All Southern B-type Stars of the Bright Star Catalogue
Authors: Levato Hugo , Grosso Mónica
Published: July 2016

We have re-determined in an homogeneous way v sin i values for all the B-type stars of the Bright Star Catalogue with southern declinations.
Stellar Rotation in Galactic Clusters
Authors: Gies Douglas R. , Huang Wenjin
Published: July 2016

Open clusters offer us the means to study stellar properties in samples with well-defined ages and initial chemical composition. Measurements of the projected rotational velocities for large numbers of cluster stars are becoming practical with the advent of multi-object spectroscopy, and such data make it possible to study the time evolution of the rotational distributions of massive stars. Investigations of these rotational distributions provide information on the angular momentum distribution in newborn clusters, the rotational spin-down due to wind loss, magnetic fields, and binary companions, and the incidence of spin-up due to mass transfer in close binaries. Here we review some of the recent observational studies and highlight some preliminary results from our work.
Rotation and Properties of Be Stars
Authors: Zorec J.
Published: July 2016

The actual characteristic average surface angular velocity ratio of the Be phenomenon may be higher than Ω/Ωc= 0.8 ± 0.1 derived fromvsinivalues not corrected from gravity darkening effects. Late Be Stars need not only higher values of Ω/Ωc, but also larger main sequence age ratios τ/τMSthan early Be Stars to display the Be phenomenon. Galactic field Be Stars appear at any MS phase, but their frequency is higher for τ/τMS≳ 0.5. Be Stars are probably neat differential rotators, i.e. they rotate with energy ratios kinetic/|gravitational| larger than withstood by critical rigid rotators. Initial formation conditions must favor the existence of fast rotators, while only a small fraction of them could be accounted for by mass transfer in close binary systems. Bn stars could perhaps represent a pre-Be phase.
Apparent Variation of v sin i and Rotational Modulation in Be Stars
Authors: Neiner C. , Jankov S. , Floquet M. , Hubert A. M.
Published: July 2016

v sin i was determined by applying the Fourier transform method to the line profiles of two classical Be Stars. A variation is observed in the apparent v sin i which corresponds to the main frequencies associated to nrp modes. Rotational modulation is observed in wind sensitive UV lines of the Be star ω Ori and is associated with an oblique magnetic dipole which is discovered for the first time in a classical Be star.
Abundance Anomalies and Rotation in Main Sequence OB Stars
Authors: Herrero A. , Lennon D. J.
Published: July 2016

We review the present status of our knowledge about observational evidence of the influence of rotation on the evolution and chemical surface enrichment of OB Main Sequence stars. We pay special attention to the CNO elements and show that luminosity class IV-V OB stars provide a good reference point for abundance analyses.

While there is clear evidence of rotationally induced mixing in OB stars, we show that fast rotation is not a guarantee of enrichment. A comparison of observed data with present evolutionary models indicates that the observed facts can be explained assuming that the stars are born with a distribution of rotational velocities, and that depending on the stellar mass the surface abundance changes will be dominated by rotation or mass loss. Only the existence of a large number of B supergiants beyond the Main Sequence cannot be explained in this scenario. We show that current evolutionary models including rotation do not adequately account for the transfer of angular momentum from the interior to the surface.

We point out that the difficulty in determining He abundances and in knowing the present or past binary status of many stars leads us to consider the above conclusions as preliminary.
CNO Abundances in Magellanic Cloud OB Supergiants
Authors: Crowther Paul A. , Evans Christopher J.
Published: July 2016

We present CNO abundance determinations in 11 Magellanic Cloud O and early B supergiants based on physical parameters obtained from FUSE, HST/IUE and VLT spectroscopy, plus model atmospheres which allow for stellar winds and line blanketing. In all cases, nitrogen is substantially enhanced whilst carbon and generally oxygen are moderately depleted, indicative of rotationally induced mixing of unprocessed and CNO processed material at their stellar surfaces.