Publications


Turbulent heating in galaxy clusters brightest in X-rays.

Nature 515 (2014) 85-87

I Zhuravleva, E Churazov, AA Schekochihin, SW Allen, P Arévalo, AC Fabian, WR Forman, JS Sanders, A Simionescu, R Sunyaev, A Vikhlinin, N Werner

The hot (10(7) to 10(8) kelvin), X-ray-emitting intracluster medium (ICM) is the dominant baryonic constituent of clusters of galaxies. In the cores of many clusters, radiative energy losses from the ICM occur on timescales much shorter than the age of the system. Unchecked, this cooling would lead to massive accumulations of cold gas and vigorous star formation, in contradiction to observations. Various sources of energy capable of compensating for these cooling losses have been proposed, the most promising being heating by the supermassive black holes in the central galaxies, through inflation of bubbles of relativistic plasma. Regardless of the original source of energy, the question of how this energy is transferred to the ICM remains open. Here we present a plausible solution to this question based on deep X-ray data and a new data analysis method that enable us to evaluate directly the ICM heating rate from the dissipation of turbulence. We find that turbulent heating is sufficient to offset radiative cooling and indeed appears to balance it locally at each radius-it may therefore be the key element in resolving the gas cooling problem in cluster cores and, more universally, in the atmospheres of X-ray-emitting, gas-rich systems on scales from galaxy clusters to groups and elliptical galaxies.


Hyperchaotic intermittent convection in a magnetized viscous fluid.

Physical review letters 112 (2014) 074502-

WM Macek, M Strumik

We consider a low-dimensional model of convection in a horizontally magnetized layer of a viscous fluid heated from below. We analyze in detail the stability of hydrodynamic convection for a wide range of two control parameters. Namely, when changing the initially applied temperature difference or magnetic field strength, one can see transitions from regular to irregular long-term behavior of the system, switching between chaotic, periodic, and equilibrium asymptotic solutions. It is worth noting that owing to the induced magnetic field a transition to hyperchaotic dynamics is possible for some parameters of the model. We also reveal new features of the generalized Lorenz model, including both type I and III intermittency.


Advective transport of interstellar plasma into the heliosphere across the reconnecting heliopause

Astrophysical Journal Letters 782 (2014)

M Strumik, S Grzedzielski, A Czechowski, WM Macek, R Ratkiewicz

We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP. © 2014. The American Astronomical Society. All rights reserved..


The Gaia-ESO Survey: processing FLAMES-UVES spectra

ASTRONOMY & ASTROPHYSICS 565 (2014) ARTN A113

GG Sacco, L Morbidelli, E Franciosini, E Majorca, S Randich, A Modigliani, G Gilmore, M Asplund, J Binney, P Bordfacio, J Drew, S Feltzing, A Ferguson, R Jeffries, G Micela, I Negueruela, T Prusti, H-W Rix, A Vallenari, E Alfaro, CA Prieto, C Babusiaux, T Bensby, R Blomme, A Bragaglia, E Flaccomio, P Francois, N Hambly, M Irwin, S Koposov, A Korn, A Lanzafame, F Pancino, A Recio-Blanco, R Smiljanic, S Van Eck, N Walton, M Bergemann, MT Costado, P de Laverny, U Heiter, V Hill, A Hourihane, R Jackson, P Jofre, J Lewis, K Lind, C Lardo, L Magrini, T Masseron, L Prisinzano, C Worley


Phase-space Lagrangian derivation of electrostatic gyrokinetics in general geometry (vol 53, 045001, 2011)

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 099501

FI Parra, I Calvo


A current driven electromagnetic mode in sheared and toroidal configurations (vol 56, 035011, 2014)

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 129501

I Pusztai, PJ Catto, FI Parra, M Barnes


Intrinsic momentum transport in up-down asymmetric tokamaks

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 095014

J Ball, FI Parra, M Barnes, W Dorland, GW Hammett, P Rodrigues, NF Loureiro


Turbulent amplification of magnetic fields in laboratory laser-produced shock waves

NATURE PHYSICS 10 (2014) 520-524

J Meinecke, HW Doyle, F Miniati, AR Bell, R Bingham, R Crowston, RP Drake, M Fatenejad, M Koenig, Y Kuramitsu, CC Kuranz, DQ Lamb, D Lee, MJ MacDonald, CD Murphy, H-S Park, A Pelka, A Ravasio, Y Sakawa, AA Schekochihin, A Scopatz, P Tzeferacos, WC Wan, NC Woolsey, R Yurchak, B Reville, G Gregori


The effect of bars on the M.-σ<inf>e</inf> relation: Offset, scatter and residuals correlations

Monthly Notices of the Royal Astronomical Society 441 (2014) 1243-1259

M Hartmann, VP Debattista, DR Cole, M Valluri, LM Widrow, J Shen

We analyse a set of collisionless disc galaxy simulations to study the consequences of bar formation and evolution on the M.-σe relation of supermassive black holes (SMBHs). The redistribution of angular momentum driven by bars leads to a mass increase within the central region, raising the velocity dispersion of the bulge, se, on average bỹ12 per cent and as much as ̃20 per cent. If a disc galaxy with an SMBH satisfying the M.-σe relation forms a bar, and the SMBH does not grow in the process, then the increase in se moves the galaxy off the M.-σe relation.We explore various effects that can affect this result including contamination from the disc and anisotropy. The displacement from theM.-σe relation for individual model barred galaxies correlates with both the bulge-to-total stellar mass ratio, M(B)/M(B + D), and the 2D anisotropy, βf(B + D), both measured within the effective radius of the bulge. Overall, this process leads to an M.-σe for barred galaxies offset from that of unbarred galaxies, as well as an increase in its scatter. We assemble samples of observed unbarred and barred galaxies with classical bulges and find tentative hints of an offset between the two consistent with the predicted. Including all barred galaxies, rather than just those with a classical bulge, leads to a significantly larger offset, which is mostly driven by the significantly larger offset of pseudo bulges. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Erratum: Long-wavelength limit of gyrokinetics in a turbulent tokamak and its intrinsic ambipolarity (Plasma Phys. Control. Fusion (2012) 54 (115007))

Plasma Physics and Controlled Fusion 56 (2014)

I Calvo, FI Parra


Observation of a new high- β and high-density state of a magnetospheric plasma in RT-1

Physics of Plasmas 21 (2014)

H Saitoh, Y Yano, Z Yoshida, M Nishiura, J Morikawa, Y Kawazura, T Nogami, M Yamasaki

A new high-β and high-density state is reported for a plasma confined in a laboratory magnetosphere. In order to expand the parameter regime of an electron cyclotron resonance heating experiment, the 8.2 GHz microwave power of the Ring Trap 1 device has been upgraded with the installation of a new waveguide system. The rated input power launched from a klystron was increased from 25 to 50 kW, which enabled the more stable formation of a hot-electron high-β plasma. The diamagnetic signal (the averaged value of four magnetic loops signals) of a plasma reached 5.2 mWb. According to a two-dimensional Grad-Shafranov analysis, the corresponding local β value is close to 100%. © 2014 AIP Publishing LLC.


Constraining the Galaxy's dark halo with RAVE stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 445 (2014) 3133-3151

T Piffl, J Binney, PJ McMillan, M Steinmetz, A Helmi, RFG Wyse, O Bienayme, J Bland-Hawthorn, K Freeman, B Gibson, G Gilmore, EK Grebel, G Kordopatis, JF Navarro, Q Parker, WA Reid, G Seabroke, A Siebert, F Watson, T Zwitter


Three-dimensional extinction mapping using Gaussian random fields

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 445 (2014) 256-269

SE Sale, J Magorrian


Interstellar medium. Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm.

Science (New York, N.Y.) 345 (2014) 791-795

J Kos, T Zwitter, R Wyse, O Bienaymé, J Binney, J Bland-Hawthorn, K Freeman, BK Gibson, G Gilmore, EK Grebel, A Helmi, G Kordopatis, U Munari, J Navarro, Q Parker, WA Reid, G Seabroke, S Sharma, A Siebert, A Siviero, M Steinmetz, FG Watson, ME Williams

The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research.


An observational and theoretical view of the radial distribution of HI gas in galaxies

Monthly Notices of the Royal Astronomical Society 441 (2014) 2159-2172

J Wang, J Fu, M Aumer, G Kauffmann, GIG Józsa, P Serra, ML Huang, J Brinchmann, T Van Der Hulst, F Bigiel

We analyse the radial distribution of HI gas for 23 disc galaxies with unusually high HI content from the Bluedisk sample, along with a similar-sized sample of 'normal' galaxies. We propose an empirical model to fit the radial profile of the HI surface density, an exponential function with a depression near the centre. The radial HI surface density profiles are very homogeneous in the outer regions of the galaxy; the exponentially declining part of the profile has a scalelength of ~0.18 R1, where R1 is the radius where the column density of the HI is 1 M⊙ pc-2. This holds for all galaxies, independent of their stellar or HI mass. The homogenous outer profiles, combined with the limited range in HI surface density in the nonexponential inner disc, results in the well-known tight relation between HI size and HI mass. By comparing the radial profiles of the HI-rich galaxies with those of the control systems, we deduce that in about half the galaxies, most of the excess gas lies outside the stellar disc, in the exponentially declining outer regions of the HI disc. In the other half, the excess is more centrally peaked. We compare our results with existing smoothed particle hydrodynamical simulations and semi-analytic models of disc galaxy formation in a Λ cold dark matter universe. Both the hydro simulations and the semi-analytic models reproduce the HI surface density profiles and the HI size-mass relation without further tuning of the simulation and model inputs. In the semi-analytic models, the universal shape of the outer HI radial profiles is a consequence of the assumption that infalling gas is always distributed exponentially. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


The formation of stellar nuclear discs in bar-induced gas inflows

Monthly Notices of the Royal Astronomical Society 445 (2014) 3352-3369

DR Cole, VP Debattista, P Erwin, SWF Earp, R Rôkar

The role of gas in themass assembly at the nuclei of galaxies is still subject to some uncertainty. Stellar nuclear discs bridge the gap between the large-scale galaxy and the central massive objects that reside there. Using a high-resolution simulation of a galaxy forming out of gas cooling and settling into a disc, we study the formation and properties of nuclear discs. Gas, driven to the centre by a bar, settles into a rotating star-forming nuclear disc (ND). This ND is thinner, younger, kinematically cooler and more metal rich than the surrounding bar. The ND is elliptical and orthogonal to the bar. The complex kinematics in the region of the ND are a result of the superposition of older stars streaming along the bar and younger stars circulating within the ND. The signature of the ND is therefore subtle in the kinematics. Instead the ND stands out clearly in metallicity and age maps. We compare the model to the density and kinematics of real galaxies with NDs finding qualitative similarities. Our results suggest that gas dissipation is very important for forming nuclear structures.


THE RELATION BETWEEN GAS DENSITY AND VELOCITY POWER SPECTRA IN GALAXY CLUSTERS: QUALITATIVE TREATMENT AND COSMOLOGICAL SIMULATIONS

ASTROPHYSICAL JOURNAL LETTERS 788 (2014) ARTN L13

I Zhuravleva, EM Churazov, AA Schekochihin, ET Lau, D Nagai, M Gaspari, SW Allen, K Nelson, IJ Parrish


Galactic kinematics and dynamics from Radial Velocity Experiment stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 439 (2014) 1231-1244

J Binney, B Burnett, G Kordopatis, M Steinmetz, G Gilmore, O Bienayme, J Bland-Hawthorn, B Famaey, EK Grebel, A Helmi, J Navarro, Q Parker, WA Reid, G Seabroke, A Siebert, F Watson, MEK Williams, RFG Wyse, T Zwitter


Analytical model of eddy currents in a reaction sphere actuator

IEEE Transactions on Magnetics 50 (2014)

M Strumik, R Wawrzaszek, M Banaszkiewicz, K Seweryn, M Sidz, E Onillon, L Rossini

A recently proposed technique to control the satellite attitude using a magnetically levitated sphere requires the development of suitable models of its dynamics. One of the phenomena that can affect motion of the system are eddy currents induced in the stator of the actuator due to time variable magnetic field generated by rotational motion of a permanent magnet rotor. We present an analytical model of the eddy currents for the actuator with eight-pole rotor. The model is derived using a second-order vector potential-based approach, and the solution is obtained in terms of spherical harmonic functions. This model allows us to study rotor rotations with constant angular frequency around an axis arbitrarily oriented with respect to both rotor and stator of the reaction sphere actuator. © 1965-2012 IEEE.


Turbulent momentum pinch of diamagnetic flows in a tokamak

ArXiv (0)

J Lee, FI Parra, M Barnes

The ion toroidal rotation in a tokamak consists of an $E\times B$ flow due to the radial electric field and a diamagnetic flow due to the radial pressure gradient. The turbulent pinch of toroidal angular momentum due to the Coriolis force studied in previous work is only applicable to the $E\times B$ flow. In this Letter, the momentum pinch for the rotation generated by the radial pressure gradient is calculated and is compared with the Coriolis pinch. This distinction is important for subsonic flows or the flow in the pedestal where the two types of flows are similar in size and opposite in direction. In the edge, the different pinches due to the opposite rotations can result in intrinsic momentum transport that gives significant rotation peaking.