1 de agosto 2012

1 de agosto 2012

1208.0001 Galactic Phase Spaces
D. CHAKRABARTY
Department of Statistics, University of Warwick, Coventry CV4 7AL, U.K.

Galaxies are argued to manifest complexity, thereby contradicting models of smooth parametric galactic phase space densities. An estimation of chaos in models of our galaxy is forwarded to suggest strength and possible causes of non-linearities in phase space. A Bayesian nonparametric methodology that is designed to acknowledge uncertainties in measured data, when applied to an observed external galaxy, indicates a non-linear galactic phase space density that could result from a bistable system potential. The effect of such a phase space structure on the inverse modelling of phase space data is discussed.
Keywords: Non-linear dynamics; Hypothesis testing; Bayesian non-parametrics

Read More: http://www.worldscientific.com/doi/abs/10.1142/9789814383295_0021

Proceedings of the 7th International Workshop on Data Analysis in Astronomy “Livio Scarsi and Vito DiGesù”
Erice, Sicily, Italy, 15 – 21 April 2011

1208.0002 Dark Matter via Many Copies of the Standard Model
Alexander Vikman
Center for Cosmology and Particle Physics, NYU, New York, NY 10003, USA

In this proceedings I review our results from [1] where we have demonstrated that baryons in many possible hidden copies of the standard model can naturally account for the dark matter. The right abundance of the hidden-sector baryons and the correct spectrum of density perturbations are simultaneously generated during modulated reheating. We have also shown that for natural values of inflaton coupling constants, dictated by unitarity, the dark-matter abundance is predicted to be proportional to the ratio of observed cosmological parameters: the square of the amplitude of cosmological perturbations and the baryon-to-photon number ratio.

Read More: http://www.worldscientific.com/doi/abs/10.1142/9789814374125_0019

Proceedings of the International School of Subnuclear Physics
Erice, Sicily, Italy, 29 August – 7 September 2009

1208.0003 21 cm cosmology in the 21st century
Jonathan R Pritchard and Abraham Loeb
Institute for Theory and Computation, Harvard University, 60 Garden St., Cambridge, MA 02138, USA
E-mail: jpritchard@cfa.harvard.edu and aloeb@cfa.harvard.edu

Imaging the Universe during the first hundreds of millions of years remains one of the exciting challenges facing modern cosmology. Observations of the redshifted 21 cm line of atomic hydrogen offer the potential of opening a new window into this epoch. This will transform our understanding of the formation of the first stars and galaxies and of the thermal history of the Universe. A new generation of radio telescopes is being constructed for this purpose with the first results starting to trickle in. In this review, we detail the physics that governs the 21 cm signal and describe what might be learnt from upcoming observations. We also generalize our
discussion to intensity mapping of other atomic and molecular lines.

Rep. Prog. Phys. 75 (2012) 086901 (35pp)

1208.0004 El 1 de agosto del 2012, Martín Huarte Espinosa, defendio su tesis doctoral en la Universidad de Cambridge (http://www.mrao.cam.ac.uk/~mh475/) Título: Modelling feedback and magnetic fields in radio galaxy evolution. Keywords: MHD, turbulence, methods: numerical, galaxies: active, intergalactic medium, galaxies: jets Abstract: The intra-cluster medium (ICM) in galaxy clusters contains magnetic fields on Mpc scales. The main probe of these cluster magnetic fields (CMFs) is the Faraday rotation of the polarized emission from radio sources that are either embedded in, or behind the ICM. Several questions are open concerning the structure and evolution of the magnetic fields in both the ICM and the radio sources. We present three-dimensional magnetohydrodynamical numerical simulations to study randomly tangled magnetic fields in the core of a cluster under the effects of light and hypersonic AGN jets. We investigate the power of the jets and carry out synthetic observations to explore the observational signatures of our model radio sources. Our polarization maps agree with the observations, and show that the magnetic structure inside the sources is shaped by the backflow of the jets. Filaments in the synthetic synchrotron emissivity maps suggest that turbulence develops in evolved sources. The polarimetry statistics correlate with time, with the viewing angle and with the jet-to-ambient density contrast. As the sources expand, the linear polarization fraction decreases and the magnetic structure inside thin sources seems more uniform than inside fat ones. Moreover, we see that the jets distort and amplify the CMFs especially at the head of the jets and that this effect correlates with the power and evolution of the jets. We find good agreement with the RM fluctuations of Hydra A. One of the most important results is that the jet-produced RM enhancements may lead to an overestimate of the strength of the CMFs by a factor of about 70%. The physics of radio source expansion may explain the flattening of the RM structure functions at large scales. The advection of metals from a central active galaxy to the ICM in a cool-core cluster is also investigated with an additional suite of hydrodynamical simulations. These metals provide information about the ICM dynamical history and of the CMFs as well. The metal distribution model of the galaxy includes metal injection via star formation. After a cooling flow is established in our simulations, highly-hypersonic and light jets are injected with a range of intermittent active phases. The resulting AGN relic bubbles advect gas and metals from the central galaxy to distances greater than 1.5 Mpc within the cluster, and intermittent jets are able to distribute the metals to larger radii than the continuous jets. The metal injection affects the general ICM metal abundances, while the galaxy metal distribution details have no effect on the dynamical evolution of the ICM metals. We find metallicity gradients similar to those observed out to ∼ 400 kpc radii.