12 research outputs found
Constraints from Faraday rotation on the magnetic field structure in the Galactic halo
We examine the constraints imposed by Faraday rotation measures of
extragalactic point sources on the structure of the magnetic field in the halo
of our Galaxy. Guided by radio polarization observations of external spiral
galaxies, we look in particular into the possibility that field lines in the
Galactic halo have an X shape. We employ the analytical models of spiraling,
possibly X-shape magnetic fields derived in a previous paper to generate
synthetic all-sky maps of the Galactic Faraday depth, which we fit to an
observational reference map with the help of Markov Chain Monte Carlo
simulations. We find that the magnetic field in the Galactic halo is slightly
more likely to be bisymmetric (azimuthal wavenumber, ) than axisymmetric
(). If it is indeed bisymmetric, it must appear as X-shaped in radio
polarization maps of our Galaxy seen edge-on from outside, but if it is
actually axisymmetric, it must instead appear as nearly parallel to the
Galactic plane.Comment: 23 pages, 23 figure
Analytical models of X-shape magnetic fields in galactic halos
External spiral galaxies seen edge-on exhibit X-shape magnetic fields in
their halos. Whether the halo of our own Galaxy also hosts an X-shape magnetic
field is still an open question. We would like to provide the necessary
analytical tools to test the hypothesis of an X-shape magnetic field in the
Galactic halo. We propose a general method to derive analytical models of
divergence-free magnetic fields whose field lines are assigned a specific
shape. We then utilize our method to obtain four particular models of X-shape
magnetic fields in galactic halos. In passing, we also derive two particular
models of predominantly horizontal magnetic fields in galactic disks. All our
field models have spiraling field lines with spatially varying pitch angle. Our
four halo field models do indeed lead to X patterns in synthetic synchrotron
polarization maps. Their precise topologies can all be explained by the action
of a wind blowing outward from the galactic disk or from the galactic center.
In practice, our field models may be used for fitting purposes or as inputs to
various theoretical problems.Comment: 16 pages, 14 figure
Measuring magnetism in the Milky Way with the Square Kilometre Array
Magnetic fields in the Milky Way are present on a wide variety of sizes and
strengths, influencing many processes in the Galactic ecosystem such as star
formation, gas dynamics, jets, and evolution of supernova remnants or pulsar
wind nebulae. Observation methods are complex and indirect; the most used of
these are a grid of rotation measures of unresolved polarized extragalactic
sources, and broadband polarimetry of diffuse emission. Current studies of
magnetic fields in the Milky Way reveal a global spiral magnetic field with a
significant turbulent component; the limited sample of magnetic field
measurements in discrete objects such as supernova remnants and HII regions
shows a wide variety in field configurations; a few detections of magnetic
fields in Young Stellar Object jets have been published; and the magnetic field
structure in the Galactic Center is still under debate.
The SKA will unravel the 3D structure and configurations of magnetic fields
in the Milky Way on sub-parsec to galaxy scales, including field structure in
the Galactic Center. The global configuration of the Milky Way disk magnetic
field, probed through pulsar RMs, will resolve controversy about reversals in
the Galactic plane. Characteristics of interstellar turbulence can be
determined from the grid of background RMs. We expect to learn to understand
magnetic field structures in protostellar jets, supernova remnants, and other
discrete sources, due to the vast increase in sample sizes possible with the
SKA. This knowledge of magnetic fields in the Milky Way will not only be
crucial in understanding of the evolution and interaction of Galactic
structures, but will also help to define and remove Galactic foregrounds for a
multitude of extragalactic and cosmological studies.Comment: 19 pages, 2 figures; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)09
PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky
PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to
ESA in response to the Call for White Papers for the definition of the L2 and
L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1)
an imager with a 3.5m mirror (cooled to 4K for high performance in the
far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and
(2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS
instrument but over three orders of magnitude more sensitive. Highlights of the
new science (beyond the obvious target of B-modes from gravity waves generated
during inflation) made possible by these two instruments working in tandem
include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters
extending to large redshift and measuring their peculiar velocities and
temperatures (through the kSZ effect and relativistic corrections to the
classic y-distortion spectrum, respectively) (2) a detailed investigation into
the nature of the cosmic infrared background (CIB) consisting of at present
unresolved dusty high-z galaxies, where most of the star formation in the
universe took place, (3) searching for distortions from the perfect CMB
blackbody spectrum, which will probe a large number of otherwise inaccessible
effects (e.g., energy release through decaying dark matter, the primordial
power spectrum on very small scales where measurements today are impossible due
to erasure from Silk damping and contamination from non-linear cascading of
power from larger length scales). These are but a few of the highlights of the
new science that will be made possible with PRISM.Comment: 20 pages Late
Modélisation de l'émission d'annihilation des positrons galactiques
TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF
Ondes et instabilités basse-fréquence dans un plasma gyrotrope (application à l'instabilité d'interchange dans les magnétosphères des planètes géantes)
TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF
Prevalence of vitamin D insufficiency in Swiss teenagers with appendicular fractures: a prospective study of 100 cases
The significance of subclinical vitamin D deficiency in the pathogenesis of fractures in children and adolescents currently remains unclear
SKA studies of in-situ synchrotron radiation from molecular clouds
Observations of the properties of dense molecular clouds are critical in understanding the process of star-formation. One of the most important, but least understood, is the role of the magnetic fields. We discuss the possibility of using high-resolution, high-sensitivity radio observations with the SKA to measure for the first time the in-situ synchrotron radiation from these molecular clouds. If the cosmic-ray (CR) particles penetrate clouds as expected, then we can measure the B-field strength directly using radio data. So far, this signature has never been detected from the collapsing clouds themselves and would be a unique probe of the magnetic field. Dense cores are typically ∼0:05 pc in size, corresponding to ∼arcsec at ∼kpc distances, and flux density estimates are ∼mJy at 1 GHz. The SKA should be able to readily detect directly, for the first time, along lines-of-sight that are not contaminated by thermal emission or complex foreground/background synchrotron emission. Polarised synchrotron may also be detectable providing additional information about the regular/turbulent fields