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Ruiz-Granados B.,University of Granada | Ruiz-Granados B.,Institute Fisica Teorica y Computacional Carlos i | Ruiz-Granados B.,Institute of Astrophysics of Canarias | Ruiz-Granados B.,University of La Laguna | And 4 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The knowledge of the regular (large scale) component of the Galactic magnetic field gives important information about the structure and dynamics of the Milky Way, and also constitutes a basic tool to determine cosmic ray trajectories. It can also provide clear windows where primordial magnetic fields could be detected. Aims. We aim to obtain the regular (large scale) pattern of the magnetic field distribution of the Milky Way that better fits the polarized synchrotron emission as seen by the WMAP satellite in the 5 years data at 22 GHz. Methods. We have done a systematic study of a number of Galactic magnetic field models: axisymmetric (with and without radial dependence on the field strength), bisymmetric (with and without radial dependence), logarithmic spiral arms, concentric circular rings with reversals and bi-toroidal. We have explored the parameter space defining each of these models using a grid-based approach. In total, more than one million models were computed. The model selection was done using a Bayesian approach. For each model, the posterior distributions were obtained and marginalized over the unwanted parameters to obtain the marginal (one-parameter) probability distribution functions. Results. In general, axisymmetric models provide a better description of the halo component, although with regard to their goodness-of-fit, the other models cannot be rejected. In the case of the disk component, the analysis is not very sensitive for obtaining the disk large-scale structure, because of the effective available area (less than 8% of the whole map and less than 40% of the disk). Nevertheless, within a given family of models, the best-fit parameters are compatible with those found in the literature. Conclusions. The family of models that better describes the polarized synchrotron halo emission is the axisymmetric one, with magnetic spiral arms with a pitch angle of ≈ 24° and a strong vertical field of 1 μG at z ≈1 kpc. When a radial variation is fitted, models require fast variations. © 2010 ESO.


Ruiz-Granados B.,University of Granada | Ruiz-Granados B.,Institute Fisica Teorica y Computacional Carlos I | Battaner E.,University of Granada | Battaner E.,Institute Fisica Teorica y Computacional Carlos I | And 6 more authors.
Astrophysical Journal Letters | Year: 2012

The study of the disk rotation curve of our Galaxy at large distances provides an interesting scenario for us to test whether magnetic fields should be considered as a non-negligible dynamical ingredient. By assuming a bulge, an exponential disk for the stellar and gaseous distributions, and a dark halo and disk magnetic fields, we fit the rotation velocity of the Milky Way. In general, when the magnetic contribution is added to the dynamics, a better description of the rotation curve is obtained. Our main conclusion is that magnetic fields should be taken into account for the Milky Way dynamics. Azimuthal magnetic field strengths of B φ ∼ 2 μG at distances of ∼2 R 0(16 kpc) are able to explain the rise-up for the rotation curve in the outer disk. © © 2012. The American Astronomical Society. All rights reserved.


Ruiz-Granados B.,Institute of Astrophysics of Canarias | Ruiz-Granados B.,University of La Laguna | Rubino-Martin J.A.,Institute of Astrophysics of Canarias | Rubino-Martin J.A.,University of La Laguna | And 4 more authors.
Astrophysical Journal Letters | Year: 2010

Recent observations of the rotation curve of M31 show a rise of the outer part that cannot be understood in terms of standard dark matter models or perturbations of the galactic disk by M31's satellites. Here, we propose an explanation of this dynamical feature based on the influence of the magnetic field within the thin disk. We have considered standard mass models for the luminous mass distribution, a Navarro-Frenk-White model to describe the dark halo, and we have added up the contribution to the rotation curve of a magnetic field in the disk, which is described by an axisymmetric pattern. Our conclusion is that a significant improvement of the fit in the outer part is obtained when magnetic effects are considered. The best-fit solution requires an amplitude of ∼4 μG with a weakradial dependence between 10 and 38 kpc. © 2010. The American Astronomical Society. All rights reserved.

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