49,897 research outputs found
The Molecular Gas in the Circumnuclear Region of Seyfert Galaxies
Sub-arcsecond IRAM Plateau de Bure mm-interferometric observations of the
12CO (2-1) line emission in the Seyfert~1 NGC 3227 and the Seyfert~2 NGC 1068
have revealed complex kinematic systems in the inner 100 pc to 300 pc that are
not consistent with pure circular motion in the host galaxies. Modeling of
these kinematic systems with elliptical orbits in the plane of the host galaxy
(representing gas motion in a bar potential) is a possible solution but does
not reproduce all features observed. A better description of the complex
kinematics is achieved by circular orbits which are tilted out of the plane of
the host galaxy. This could indicate that the thin circumnuclear gas disk is
warped. In the case of NGC 1068 the warp model suggests that at a radius of
about 70 pc, the gas disk is oriented edge-on providing material for the
obscuration of the AGN nucleus. The position-velocity diagrams show rising
rotation curves at r 2
x 10^7 M_solar for NGC 3227 and > 10^8 M_solar for NGC 1068 within the central
25 pc.Comment: 14 pages, Ap.J. letter, accepte
Identification of red supergiants in nearby galaxies with mid-IR photometry
The role of episodic mass loss in massive star evolution is one of the most
important open questions of current stellar evolution theory. Episodic mass
loss produces dust and therefore causes evolved massive stars to be very
luminous in the mid-infrared and dim at optical wavelengths. We aim to increase
the number of investigated luminous mid-IR sources to shed light on the late
stages of these objects. To achieve this we employed mid-IR selection criteria
to identity dusty evolved massive stars in two nearby galaxies. The method is
based on mid-IR colors, using 3.6 {\mu}m and 4.5 {\mu}m photometry from
archival Spitzer Space Telescope images of nearby galaxies and J-band
photometry from 2MASS. We applied our criteria to two nearby star-forming dwarf
irregular galaxies, Sextans A and IC 1613, selecting eight targets, which we
followed up with spectroscopy. Our spectral classification and analysis yielded
the discovery of two M-type supergiants in IC 1613, three K-type supergiants
and one candidate F-type giant in Sextans A, and two foreground M giants. We
show that the proposed criteria provide an independent way for identifying
dusty evolved massive stars, that can be extended to all nearby galaxies with
available Spitzer/IRAC images at 3.6 {\mu}m and 4.5 {\mu}m.Comment: 8 pages, 4 figures, A&A in pres
Phenomenology Tools on Cloud Infrastructures using OpenStack
We present a new environment for computations in particle physics
phenomenology employing recent developments in cloud computing. On this
environment users can create and manage "virtual" machines on which the
phenomenology codes/tools can be deployed easily in an automated way. We
analyze the performance of this environment based on "virtual" machines versus
the utilization of "real" physical hardware. In this way we provide a
qualitative result for the influence of the host operating system on the
performance of a representative set of applications for phenomenology
calculations.Comment: 25 pages, 12 figures; information on memory usage included, as well
as minor modifications. Version to appear in EPJ
Sites for Gamma-ray Astronomy in Argentina
We have searched for possible sites in Argentina for the installation of
large air Cherenkov telescope arrays and water Cherenkov systems. At present
seven candidates are identified at altitudes from 2500 to 4500 m. The highest
sites are located at the Northwest of the country, in La Puna. Sites at 2500
and 3100 m are located in the West at El Leoncito Observatory, with excellent
infrastructure. A description of these candidate sites is presented with
emphasis on infrastructure and climatology.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Shear Flow Generation and Energetics in Electromagnetic Turbulence
Zonal flows are recognised to play a crucial role for magnetised plasma
confinement. The genesis of these flows out of turbulent fluctuations is
therefore of significant interest. We investigate the relative importance of
zonal flow generation mechanisms via the Reynolds stress, Maxwell stress, and
geodesic acoustic mode (GAM) transfer in drift-Alfv\'en turbulence. By means of
numerical computations we quantify the energy transfer into zonal flows owing
to each of these effects. The importance of the three driving ingredients in
electrostatic and electromagnetic turbulence for conditions relevant to the
edge of fusion devices is revealed for a broad range of parameters. The
Reynolds stress is found to provide a flow drive, while the electromagnetic
Maxwell stress is in the cases considered a sink for the flow energy. In the
limit of high plasma beta, where electromagnetic effects and Alfv\'en dynamics
are important, the Maxwell stress is found to cancel the Reynolds stress to a
high degree. The geodesic oscillations, related to equilibrium pressure profile
modifications due to poloidally asymmetric transport, can act as both sinks as
drive terms, depending on the parameter regime. For high beta cases the GAMs
are the main drive of the flow. This is also reflected in the frequency
dependence of the flow, showing a distinct peak at the GAM frequency in that
regime.Comment: 16 pages, 12 Figure
Exact Matrix Product States for Quantum Hall Wave Functions
We show that the model wave functions used to describe the fractional quantum
Hall effect have exact representations as matrix product states (MPS). These
MPS can be implemented numerically in the orbital basis of both finite and
infinite cylinders, which provides an efficient way of calculating arbitrary
observables. We extend this approach to the charged excitations and numerically
compute their Berry phases. Finally, we present an algorithm for numerically
computing the real-space entanglement spectrum starting from an arbitrary
orbital basis MPS, which allows us to study the scaling properties of the
real-space entanglement spectra on infinite cylinders. The real-space
entanglement spectrum obeys a scaling form dictated by the edge conformal field
theory, allowing us to accurately extract the two entanglement velocities of
the Moore-Read state. In contrast, the orbital space spectrum is observed to
scale according to a complex set of power laws that rule out a similar
collapse.Comment: 10 pages and Appendix, v3 published versio
Soliton-dynamical approach to a noisy Ginzburg-Landau model
We present a dynamical description and analysis of non-equilibrium
transitions in the noisy Ginzburg-Landau equation based on a canonical phase
space formulation. The transition pathways are characterized by nucleation and
subsequent propagation of domain walls or solitons. We also evaluate the
Arrhenius factor in terms of an associated action and find good agreement with
recent numerical optimization studies.Comment: 4 pages (revtex4), 3 figures (eps
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