Publications


The SAURON project - XXI. The spatially resolved UV-line strength relations of early-type galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 423 (2012) 1921-1939

H Jeong, SK Yi, M Bureau, RL Davies, R Bacon, M Cappellari, PT de Zeeuw, E Emsellem, J Falcon-Barroso, D Krajnovic, H Kuntschner, RM McDermid, RF Peletier, M Sarzi, RCE van den Bosch, G van de Ven


A study of fast electron energy transport in relativistically intense laser-plasma interactions with large density scalelengths

Physics of Plasmas 19 (2012)

RHH Scott, CP Ridgers, SJ Rose, PA Norreys, KL Lancaster, RMGM Trines, AR Bell, M Tzoufras, F Perez, SD Baton, JJ Santos, P Nicolai, S Hulin, JR Davies

A systematic experimental and computational investigation of the effects of three well characterized density scalelengths on fast electron energy transport in ultra-intense laser-solid interactions has been performed. Experimental evidence is presented which shows that, when the density scalelength is sufficiently large, the fast electron beam entering the solid-density plasma is best described by two distinct populations: those accelerated within the coronal plasma (the fast electron pre-beam) and those accelerated near or at the critical density surface (the fast electron main-beam). The former has considerably lower divergence and higher temperature than that of the main-beam with a half-angle of ∼20°. It contains up to 30% of the total fast electron energy absorbed into the target. The number, kinetic energy, and total energy of the fast electrons in the pre-beam are increased by an increase in density scalelength. With larger density scalelengths, the fast electrons heat a smaller cross sectional area of the target, causing the thinnest targets to reach significantly higher rear surface temperatures. Modelling indicates that the enhanced fast electron pre-beam associated with the large density scalelength interaction generates a magnetic field within the target of sufficient magnitude to partially collimate the subsequent, more divergent, fast electron main-beam. © 2012 American Institute of Physics.


Comparative merits of the memory function and dynamic local-field correction of the classical one-component plasma

PHYSICAL REVIEW E 85 (2012) ARTN 056407

JP Mithen, J Daligault, G Gregori


The opto-mechanical design of HARMONI: A first light integral field spectrograph for the E-ELT

Proceedings of SPIE - The International Society for Optical Engineering 8446 (2012)

NA Thatte, M Tecza, F Clarke, J Lynn, RL Davies, S Arribas, J Kosmalski, R Bacon, A Remillieux, AB Fragoso-Lopez, J Fuentes, F Gracia, D Sosa, E Mediavilla, D Freeman, T Fusco, F Gago, AM Gallie, D Montgomery, D Lunney, H Schnetler, A Garcia

HARMONI is a visible and near-IR integral field spectrograph, providing the E-ELT's spectroscopic capability at first light. It obtains simultaneous spectra of 32000 spaxels, at a range of resolving powers from R∼4000 to R∼20000, covering the wavelength range from 0.47 to 2.45 ìm. The 256 ? 128 spaxel field of view has four different plate scales, with the coarsest scale (40 mas) providing a 5? ? 10? FoV, while the finest scale is a factor of 10 finer (4mas). We describe the opto-mechanical design of HARMONI, prior to the start of preliminary design, including the main subsystems - namely the image de-rotator, the scale-changing optics, the splitting and slicing optics, and the spectrographs. We also present the secondary guiding system, the pupil imaging optics, the field and pupil stops, the natural guide star wavefront sensor, and the calibration unit. © 2012 SPIE.


Angular momentum transfer to a Milky Way disk at high redshift

ArXiv (2012)

H Tillson, J Devriendt, A Slyz, L Miller, C Pichon

An Adaptive Mesh Refinement cosmological resimulation is analyzed in order to test whether filamentary flows of cold gas are responsible for the build-up of angular momentum within a Milky Way like disk at z>=3. A set of algorithms is presented that takes advantage of the high spatial resolution of the simulation (12 pc) to identify: (i) the central gas disk and its plane of orientation; (ii) the complex individual filament trajectories that connect to the disk, and; (iii) the infalling satellites. The results show that two filaments at z>5.5, which later merge to form a single filament at z<4, drive the angular momentum and mass budget of the disk throughout its evolution, whereas luminous satellite mergers make negligible fractional contributions. Combined with the ubiquitous presence of such filaments in all large-scale cosmological simulations that include hydrodynamics, these findings provide strong quantitative evidence that the growth of thin disks in haloes with masses below 10^{12} M_{sun}, which host the vast majority of galaxies, is supported via inflowing streams of cold gas at intermediate and high redshifts.


Inelastic x-ray scattering from shocked liquid deuterium

Physical Review Letters 109 (2012)

SP Regan, PB Radha, SX Hu, TR Boehly, DD Meyerhofer, TC Sangster, K Falk, G Gregori, BJB Crowley, CD Murphy, SH Glenzer, OL Landen, T Döppner, DO Gericke, J Vorberger

The Fermi-degenerate plasma conditions created in liquid deuterium by a laser-ablation - driven shock wave were probed with noncollective, spectrally resolved, inelastic x-ray Thomson scattering employing Cl Ly line emission at 2.96 keV. These first x-ray Thomson scattering measurements of the microscopic properties of shocked deuterium show an inferred spatially averaged electron temperature of 8±5 eV, an electron density of 2.2(±0.5)×1023 cm3, and an ionization of 0.8 (-0.25, +0.15). Two-dimensional hydrodynamic simulations using equation-of-state models suited for the extreme parameters occurring in inertial confinement fusion research and planetary interiors are consistent with the experimental results. © 2012 American Physical Society.


Testing quantum mechanics in non-Minkowski space-time with high power lasers and 4 th generation light sources

Scientific Reports 2 (2012)

BJB Crowley, R Bingham, RG Evans, DO Gericke, OL Landen, CD Murphy, PA Norreys, SJ Rose, T Tschentscher, CH-T Wang, JS Wark, G Gregori

A common misperception of quantum gravity is that it requires accessing energies up to the Planck scale of 10 19 GeV, which is unattainable from any conceivable particle collider. Thanks to the development of ultra-high intensity optical lasers, very large accelerations can be now the reached at their focal spot, thus mimicking, by virtue of the equivalence principle, a non Minkowski space-time. Here we derive a semiclassical extension of quantum mechanics that applies to different metrics, but under the assumption of weak gravity. We use our results to show that Thomson scattering of photons by uniformly accelerated electrons predicts an observable effect depending upon acceleration and local metric. In the laboratory frame, a broadening of the Thomson scattered x ray light from a fourth generation light source can be used to detect the modification of the metric associated to electrons accelerated in the field of a high power optical laser.


The non-thermal emission of extended radio galaxy lobes with curved electron spectra

ArXiv (2011)

P Duffy, KM Blundell

The existing theoretical framework for the energies stored in the synchrotron-emitting lobes of radio galaxies and quasars doesn't properly account for the curved spectral shape that many of them exhibit. We characterise these spectra using parameters that are straightforwardly observable in the era of high-resolution, low-frequency radio astronomy: the spectral curvature and the turnover in the frequency spectrum. This characterisation gives the Lorentz factor at the turnover in the energy distribution (we point out that this is distinctly different from the Lorentz factor corresponding to the turnover frequency in a way that depends on the amount of curvature in the spectrum) and readily gives the equipartition magnetic field strength and the total energy of the radiating plasma obviating the need for any assumed values of the cutoff frequencies to calculate these important physical quantities. This framework readily yields the form of the X-ray emission due to inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by the electrons in the plasma having Lorentz factors of $\sim$1000. We also present the contribution to CMB anisotropies due to relativistic plasmas such as giant radio galaxy lobes, expressed in terms of the extent to which the lobes have their magnetic field and particle energies are in equipartition with one another.


Self-organized electromagnetic field structures in laser-produced counter-streaming plasmas

Nature Physics 8 (2012) 809-812

NL Kugland, DD Ryutov, SH Glenzer, MC Levy, C Plechaty, BA Remington, JS Ross, H-S Park, P-Y Chang, G Fiksel, DH Froula, RP Drake, M Grosskopf, C Kuranz, G Gregori, J Meinecke, B Reville, M Koenig, A Pelka, A Ravasio, Y Kuramitsu, T Morita, Y Sakawa, H Takabe, E Liang, F Miniati, R Presura, A Spitkovsky

Self-organization occurs in plasmas when energy progressively transfers from smaller to larger scales in an inverse cascade. Global structures that emerge from turbulent plasmas can be found in the laboratory and in astrophysical settings; for example, the cosmic magnetic field, collisionless shocks in supernova remnants and the internal structures of newly formed stars known as Herbig-Haro objects. Here we show that large, stable electromagnetic field structures can also arise within counter-streaming supersonic plasmas in the laboratory. These surprising structures, formed by a yet unexplained mechanism, are predominantly oriented transverse to the primary flow direction, extend for much larger distances than the intrinsic plasma spatial scales and persist for much longer than the plasma kinetic timescales. Our results challenge existing models of counter-streaming plasmas and can be used to better understand large-scale and long-time plasma self-organization. © 2012 Macmillan Publishers Limited. All rights reserved.


Dynamics of secular evolution

ArXiv (2012)

J Binney

The text of lectures to the 2011 Tenerife Winter School. The School's theme was "Secular Evolution of Galaxies" and my task was to present the underlying stellar-dynamical theory. Other lecturers were speaking on the role of bars and chemical evolution, so these topics are avoided here. We start with an account of the connections between isolating integrals, quasiperiodicity and angle-action variables - these variables played a unifying role throughout the lectures. This leads on to the phenomenon of resonant trapping and how this can lead to chaos in cuspy potentials and phase-space mixing in slowly evolving potentials. Surfaces of section and frequency analysis are introduced as diagnostics of phase-space structure. Real galactic potentials include a fluctuating part that drives the system towards unattainable thermal equilibrium. Two-body encounters are only one source of fluctuations, and all fluctuations will drive similar evolution. We derive the orbit-averaged Fokker-Planck equation and relations that hold between the second-order diffusion coefficients and both the power spectrum of the fluctuations and the first-order diffusion coefficients. From the observed heating of the solar neighbourhood we show that the second-order diffusion coefficients must scale as J^{1/2}. We show that periodic spiral structure shifts angular momentum outwards, heating at the Lindblad resonances and mixing at corotation. The equation that would yield the normal modes of a stellar disc is first derived and then used to discuss the propagation of tightly-wound spiral waves. The winding up of such waves is explains why cool stellar discs are responsive systems that amplify ambient noise. An explanation is offered of why the Lin-Shu-Kalnajs dispersion relation and even global normal-mode calculations provide a very incomplete understanding of the dynamics of stellar discs.


Measurement of radiative shock properties by X-ray Thomson scattering

Physical Review Letters 108 (2012)

AJ Visco, RP Drake, MJ Grosskopf, SH Glenzer, T Döppner, G Gregori, DH Froula

X-ray Thomson scattering has enabled us to measure the temperature of a shocked layer, produced in the laboratory, that is relevant to shocks emerging from supernovas. High energy lasers are used to create a shock in argon gas which is probed by x-ray scattering. The scattered, inelastic Compton feature allows inference of the electron temperature. It is measured to be 34 eV in the radiative precursor and ∼60eV near the shock. Comparison of energy fluxes implied by the data demonstrates that the shock wave is strongly radiative. © 2012 American Physical Society.


Concepts in Thermal Physics 2nd Edition

, 2012

SJ Blundell, KM Blundell


A new formula for disc kinematics

Monthly Notices of the Royal Astronomical Society 419 (2012) 1546-1556

R Schönrich, J Binney

In a disc galaxy, the distribution of azimuthal components of velocity is very skew. In the past, this skewness has been modelled by superposed Gaussians. We use dynamical arguments to derive an analytic formula that can be fitted to observed velocity distributions, and validate it by fits to the velocities derived from a dynamically rigorous model, and to a sample of local stars with accurate space velocities. Our formula is much easier to use than a full distribution function. It has fewer parameters than a multi-Gaussian fit, and the best-fitting model parameters give insight into the underlying disc dynamics. In particular, once the azimuthal velocities of a sample have been successfully fitted, the apparatus provides a prediction for the corresponding distribution of radial velocitiesvR. An effective formula like ours is invaluable when fitting to data for stars at some distance from the Sun because it enables one to make proper allowance for the errors in distance and proper motion when determining the underlying disc kinematics. The derivation of our formula elucidates the way the horizontal and vertical motions are closely intertwined, and makes it evident that no stellar population can have a scaleheight and vertical velocity dispersions that are simultaneously independent of radius. We show that the oscillation of a star perpendicular to the Galactic plane modifies the effective potential in which the star moves radially in such a way that the more vertical energy a star has, the larger is the mean radius of its orbit. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


XUV spectroscopic characterization of warm dense aluminum plasmas generated by the free-electron-laser FLASH

Laser and Particle Beams 30 (2012) 45-56

U Zastrau, I Uschmann, E Förster, T Burian, J Chalupsky, L Juha, T Döppner, C Fortmann, SH Glenzer, RW Lee, AJ Nelson, TWJ Dzelzainis, CLS Lewis, D Riley, RR Fäustlin, N Medvedev, S Toleikis, E Galtier, HJ Lee, B Nagler, FB Rosmej, G Gregori, SM Vinko, JS Wark, T Whitcher, T Tschentscher

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 μJ are focused to intensities ranging between 10 and 10 W/cm . We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations. © 2012 Cambridge University Press.


AGN feedback driven molecular outflow in NGC 1266

Proceedings of the International Astronomical Union 8 (2012) 175-176

K Alatalo, G Graves, KE Nyland, LM Young, L Blitz, S Deustua, J Wrobel, TA Davis, PT De Zeeuw, E Emsellem, D Krajnovic, H Kuntschner, M Bureau, E Bayet, M Cappellari, RL Davies, M Bois, F Bournaud, S Khochfar, T Naab, S Martín, RM Mcdermid, R Morganti, M Sarzi, P Serra, N Scott, A Weijmans

NGC 1266 is a nearby field galaxy observed as part of the ATLAS survey (Cappellari et al. 2011). NGC 1266 has been shown to host a compact (< 200 pc) molecular disk and a mass-loaded molecular outflow driven by the AGN (Alatalo et al. 2011). Very Long Basline Array (VLBA) observations at 1.65 GHz revealed a compact (diameter < 1.2 pc), high brightness temperature continuum source most consistent with a low-level AGN origin. The VLBA continuum source is positioned at the center of the molecular disk and may be responsible for the expulsion of molecular gas in NGC 1266. Thus, the candidate AGN-driven molecular outflow in NGC 1266 supports the picture in which AGNs do play a significant role in the quenching of star formation and ultimately the evolution of the red sequence of galaxies. © International Astronomical Union 2013.


Three-Dimensional Structure of Solar Wind Turbulence

ArXiv (2011)

CHK Chen, A Mallet, AA Schekochihin, TS Horbury, RT Wicks, SD Bale

We present a measurement of the scale-dependent, three-dimensional structure of the magnetic field fluctuations in inertial range solar wind turbulence with respect to a local, physically motivated coordinate system. The Alfvenic fluctuations are three-dimensionally anisotropic, with the sense of this anisotropy varying from large to small scales. At the outer scale, the magnetic field correlations are longest in the local fluctuation direction, consistent with Alfven waves. At the proton gyroscale, they are longest along the local mean field direction and shortest in the direction perpendicular to the local mean field and the local field fluctuation. The compressive fluctuations are highly elongated along the local mean field direction, although axially symmetric perpendicular to it. Their large anisotropy may explain why they are not heavily damped in the solar wind.


Subcritical fluctuations and suppression of turbulence in differentially rotating gyrokinetic plasmas

PLASMA PHYSICS AND CONTROLLED FUSION 54 (2012) ARTN 055011

AA Schekochihin, EG Highcock, SC Cowley


Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves

Nature 481 (2012) 480-483

G Gregori, CD Murphy, K Schaar, A Baird, AR Bell, M Edwards, W Lau, J Mithen, B Reville, S Yang, R Bingham, APL Robinson, A Ravasio, A Benuzzi-Mounaix, M Koenig, C Constantin, ET Everson, C Niemann, RP Drake, CD Gregory, NC Woolsey, Y Kuramitsu, Y Sakawa, H-S Park, BA Remington, DD Ryutov, F Miniati

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10 gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution. © 2012 Macmillan Publishers Limited. All rights reserved.


Employing laser-accelerated proton beams to diagnose high intensity laser-plasma interactions

AIP Conference Proceedings 1462 (2012) 149-154

G Sarri, K Quinn, M Borghesi, CA Cecchetti, PA Norreys, R Trines, O Willi, J Fuchs, P McKenna, M Quinn, F Pegoraro, SV Bulanov

A review of the proton radiography technique will be presented. This technique employs laser-accelerated laminar bunches of protons to diagnose the temporal and spatial characteristic of the electric and magnetic fields generated during high-intensity laser-plasma interactions. The remarkable temporal and spatial resolution that this technique can achieve (of the order of a picosecond and a few microns respectively) candidates this technique as the preferrable one, if compared to other techniques, to probe high intensity laser-matterinteractions. © 2012 American Institute of Physics.


The properties of the local spiral arms from RAVE data: two-dimensional density wave approach

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 425 (2012) 2335-2342

A Siebert, B Famaey, J Binney, B Burnett, C Faure, I Minchev, MEK Williams, O Bienayme, J Bland-Hawthorn, C Boeche, BK Gibson, EK Grebel, A Helmi, A Just, U Munari, JF Navarro, QA Parker, WA Reid, G Seabroke, A Siviero, M Steinmetz, T Zwitter