Magnetic Field Seeding by Galactic Winds

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure formation shocks and galactic outflows. In this work we investigate how efficiently galactic winds can provide an intense and widespread "seed" magnetisation. This may be used to explain the magnetic fields observed today in clusters of galaxies and in the intergalactic medium (IGM). We use semi-analytic simulations of magnetised galactic winds coupled to high resolution N-body simulations of structure formation to estimate lower and upper limits for the fraction of the IGM which can be magnetised up to a specified level. We find that galactic winds are able to seed a substantial fraction of the cosmic volume with magnetic fields. Most regions affected by winds have magnetic fields in the range -12 < Log B < -8 G, while higher seed fields can be obtained only rarely and in close proximity to wind-blowing galaxies. These seed fields are sufficiently intense for a moderately efficient turbulent dynamo to amplify them to the observed values. The volume filling factor of the magnetised regions strongly depends on the efficiency of winds to load mass from the ambient medium. However, winds never completely fill the whole Universe and pristine gas can be found in cosmic voids and regions unaffected by feedback even at z=0. This means that, in principle, there might be the possibility to probe the existence of primordial magnetic fields in such regions.Comment: 14 pages, 5 figures. Accepted for publications by MNRAS. A high resolution version of the paper is available at http://astronomy.sussex.ac.uk/~sb207/Papers/bb.ps.g

The last orbit of binary black holes

We have used our new technique for fully numerical evolutions of orbiting black-hole binaries without excision to model the last orbit and merger of an equal-mass black-hole system. We track the trajectories of the individual apparent horizons and find that the binary completed approximately one and a third orbits before forming a common horizon. Upon calculating the complete gravitational radiation waveform, horizon mass, and spin, we find that the binary radiated 3.2% of its mass and 24% of its angular momentum. The early part of the waveform, after a relatively short initial burst of spurious radiation, is oscillatory with increasing amplitude and frequency, as expected from orbital motion. The waveform then transitions to a typical `plunge' waveform; i.e. a rapid rise in amplitude followed by quasinormal ringing. The plunge part of the waveform is remarkably similar to the waveform from the previously studied `ISCO' configuration. We anticipate that the plunge waveform, when starting from quasicircular orbits, has a generic shape that is essentially independent of the initial separation of the binary.Comment: 5 pages, 5 figures, revtex

Chromospheric CaII Emission in Nearby F, G, K, and M stars

We present chromospheric CaII activity measurements, rotation periods and ages for ~1200 F-, G-, K-, and M- type main-sequence stars from ~18,000 archival spectra taken at Keck and Lick Observatories as a part of the California and Carnegie Planet Search Project. We have calibrated our chromospheric S values against the Mount Wilson chromospheric activity data. From these measurements we have calculated median activity levels and derived R'HK, stellar ages, and rotation periods for 1228 stars, ~1000 of which have no previously published S values. We also present precise time series of activity measurements for these stars.Comment: 62 pages, 7 figures, 1 table. Second (extremely long) table is available at http://astro.berkeley.edu/~jtwright/CaIIdata/tab1.tex Accepted by ApJ

Kondo Insulator description of spin state transition in FeSb2

The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees with a picture of a temperature induced spin state transition within the Fe t_{2g} multiplet. However, high pressure powder diffraction data show no sign of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been extracted and the temperature dependence of the Gruneisen parameter has been determined. We discuss here the relevance of a Kondo insulator description for this material.Comment: Physical Review B in press (2005

Accurate Evolutions of Orbiting Black-Hole Binaries Without Excision

We present a new algorithm for evolving orbiting black-hole binaries that does not require excision or a corotating shift. Our algorithm is based on a novel technique to handle the singular puncture conformal factor. This system, based on the BSSN formulation of Einstein's equations, when used with a `pre-collapsed' initial lapse, is non-singular at the start of the evolution, and remains non-singular and stable provided that a good choice is made for the gauge. As a test case, we use this technique to fully evolve orbiting black-hole binaries from near the Innermost Stable Circular Orbit (ISCO) regime. We show fourth order convergence of waveforms and compute the radiated gravitational energy and angular momentum from the plunge. These results are in good agreement with those predicted by the Lazarus approach.Comment: 4 pages, revtex4, 3 figs, references added, typos fixe

Pacman (II): Application and Statistical Characterisation of Improved RM Maps

We proposed a new method -- "Pacman" -- to calculate Faraday rotation measure (RM) maps from multi-frequency polarisation angle data (Dolag et al.) in order to avoid the so-called n-pi ambiguity. Here, we apply our "Pacman" algorithm to two polarisation data sets of extended radio sources in the Abell 2255 and the Hydra A cluster, and compare the RM maps obtained using "Pacman" to RM maps obtained employing already existing methods. Thereby, we provide a new high quality RM map of the Hydra north lobe which is in a good agreement with the existing one but find significant differences in the case of the south lobe of Hydra A. We demonstrate the reliability and the robustness of "Pacman". In order to study the influence of map making artefacts, which are imprinted by wrong solutions to the n-pi ambiguities, and of the error treatment of the data, we calculated and compared magnetic field power spectra from various RM maps. The power spectra were derived using the method recently proposed by Ensslin & Vogt (2003). We demonstrate the sensitivity of statistical analysis to artefacts and noise in the RM maps and thus, we demonstrate the importance of an unambiguous determination of RM maps and an understanding of the nature of the noise in the data. We introduce and perform statistical tests to estimate the quality of the derived RM maps, which demonstrate the quality improvements due to "Pacman".Comment: revised version, accepted, MNRAS in pres

Research in particles and fields

The astrophysical aspects of cosmic rays and gamma rays and of the electromagnetic field environment of the Earth and other planets are investigated. These investigations are carried out by means of energetic particle and photon detector systems flown on spacecraft and balloons

A two-dimensional Fermi liquid with attractive interactions

We realize and study an attractively interacting two-dimensional Fermi liquid. Using momentum resolved photoemission spectroscopy, we measure the self-energy, determine the contact parameter of the short-range interaction potential, and find their dependence on the interaction strength. We successfully compare the measurements to a theoretical analysis, properly taking into account the finite temperature, harmonic trap, and the averaging over several two-dimensional gases with different peak densities