Transport in quasiperiodic interacting systems: from superdiffusion to subdiffusion

Using a combination of numerically exact and renormalization-group techniques we study the nonequilibrium transport of electrons in an one-dimensional interacting system subject to a quasiperiodic potential. For this purpose we calculate the growth of the mean-square displacement as well as the melting of domain walls. While the system is nonintegrable for all studied parameters, there is no on finite region default of parameters for which we observe diffusive transport. In particular, our model shows a rich dynamical behavior crossing over from superdiffusion to subdiffusion. We discuss the implications of our results for the general problem of many-body localization, with a particular emphasis on the rare region Griffiths picture of subdiffusion.Comment: 6 pages, 5 figures. A more detailed analysis of the dynamical exponents extraction and discussion of the relevant times. Adds a log-derivative for the FRG sectio

A high-resolution mm and cm study of the obscured LIRG NGC 4418 - A compact obscured nucleus fed by in-falling gas?

The aim of this study is to constrain the dynamics, structure and feeding of the compact nucleous of NGC4418, and to reveal the nature of the main hidden power source: starburst or AGN. We obtained high spatial resolution observations of NGC4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA very extended configuration. We use the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate and the dust temperature. Emission lines are used to study the kinematics through position-velocity diagrams. Molecular emission is studied with population diagrams and by fitting an LTE synthetic spectrum. We detect bright 1mm line emission from CO, HC3N, HNC and C34S, and 1.4 GHz absorption from HI. The CO 2-1 emission and HI absorption can be fit by two velocity components at 2090 and 2180 km s-1. We detect vibrationally excited HC3N and HNC, with Tvib 300K. Molecular excitation is consistent with a layered temperature structure, with three main components at 80, 160 and 300 K. For the hot component we estimate a source size of less than 5 pc. The nuclear molecular gas surface density of 1e4 Msun pc-2 is extremely high, and similar to that found in the ultra-luminous infrared galaxy (ULIRG) Arp220. Our observations confirm the the presence of a molecular and atomic in-flow, previously suggested by Herschel observations, which is feeding the activity in the center of NGC4418. Molecular excitation confirms the presence of a very compact, hot dusty core. If a starburst is responsible for the observed IR flux, this has to be at least as extreme as the one in Arp220, with an age of 3-10 Myr and a star formation rate >10 Msun yr-1. If an AGN is present, it must be extremely Compton-thick.Comment: 18 pages, 11 figures, Accepted for publication by A&A on 10/6/201

A close-pair binary in a distant triple supermassive black-hole system

Galaxies are believed to evolve through merging, which should lead to multiple supermassive black holes in some. There are four known triple black hole systems, with the closest pair being 2.4 kiloparsecs apart (the third component is more distant at 3 kiloparsecs), which is far from the gravitational sphere of influence of a black hole with mass $\sim$10$^9$ M$_\odot$ (about 100 parsecs). Previous searches for compact black hole systems concluded that they were rare, with the tightest binary system having a separation of 7 parsecs. Here we report observations of a triple black hole system at redshift z=0.39, with the closest pair separated by $\sim$140 parsecs. The presence of the tight pair is imprinted onto the properties of the large-scale radio jets, as a rotationally-symmetric helical modulation, which provides a useful way to search for other tight pairs without needing extremely high resolution observations. As we found this tight pair after searching only six galaxies, we conclude that tight pairs are more common than hitherto believed, which is an important observational constraint for low-frequency gravitational wave experiments.Comment: 21 pages, 6 figures. Published online by Nature on 25 June 2014. Extremely minor differences with published version exis

The cosmic radio dipole: Bayesian estimators on new and old radio surveys

The cosmic radio dipole is an anisotropy in the number counts of radio sources, analogous to the dipole seen in the cosmic microwave background (CMB). Measurements of source counts of large radio surveys have shown that though the radio dipole is generally consistent in direction with the CMB dipole, the amplitudes are in tension. These observations present an intriguing puzzle as to the cause of this discrepancy, with a true anisotropy breaking with the assumptions of the cosmological principle, invalidating the most common cosmological models that are built on these assumptions. We present a novel set of Bayesian estimators to determine the cosmic radio dipole and compare the results with commonly used methods on the Rapid ASKAP Continuum Survey (RACS) and the NRAO VLA Sky Survey (NVSS) radio surveys. In addition, we adapt the Bayesian estimators to take into account systematic effects known to affect such large radio surveys, folding information such as the local noise floor or array configuration directly into the parameter estimation. The enhancement of these estimators allows us to greatly increase the amount of sources used in the parameter estimation, yielding tighter constraints on the cosmic radio dipole estimation than previously achieved with NVSS and RACS. We extend the estimators further to work on multiple catalogues simultaneously, leading to a combined parameter estimation using both NVSS and RACS. The result is a dipole estimate that perfectly aligns with the CMB dipole in terms of direction but with an amplitude that is three times as large, and a significance of 4.8$\sigma$. This new dipole measurement is made to an unprecedented level of precision for radio sources, which is only matched by recent results using infrared quasars.Comment: 14 pages, 11 figures. Accepted for publication in Astronomy & Astrophysic

The OH Megamaser Emission in Arp\,220: the rest of the story

The OH Megamaser emission in the merging galaxy Arp220 has been re-observed with the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European VLBI Network (EVN). Imaging results of the OH line emission at the two nuclei are found to be consistent with earlier observations and confirm additional extended emission structures surrounding the nuclei. Detailed information about the distributed emission components around the two nuclei has been obtained using a concatenated MERLIN and EVN database with intermediate (40 mas) spatial resolution. Continuum imaging shows a relatively compact West nucleus and a more extended East nucleus in addition to an extended continuum ridge stretching below and beyond the two nuclei. Spectral line imaging show extended emission regions at both nuclei together with compact components and additional weaker components north and south of the West nucleus. Spectral line analysis indicates that the dominant OH line emission originates in foreground molecular material that is part of a large-scale molecular structure that engulfs the whole nuclear region. Compact OH components are representative of star formation regions within the two nearly edge-on nuclei and define the systemic velocities of East and West as 5425 km/s and 5360 km/s. The foreground material at East and West has a 100 km/s lower velocity at 5314 and 5254 km/s. These emission results confirm a maser amplification scenario where the background continuum and the line emission of the star formation regions are amplified by foreground masering material that is excited by the FIR radiation field originating in the two nuclear regions.Comment: 17 pages, 18 figure

Optical Control of Field-Emission Sites by Femtosecond Laser Pulses

We have investigated field emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses. Strongly asymmetric modulations of the field emission intensity distributions are observed depending on the polarization of the light and the laser incidence direction relative to the azimuthal orientation of tip apex. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity on the 10 nm scale. Simulations of local fields on the tip apex and of electron emission patterns based on photo-excited nonequilibrium electron distributions explain our observations quantitatively.Comment: 4 pages, submitted to Physical Review Letter

The preferentially magnified active nucleus in IRAS F10214+4724 - III. VLBI observations of the radio core

We report 1.7GHz very long baseline interferometry (VLBI) observations of IRAS F10214+4724, a lensed z = 2.3 obscured quasar with prodigious star formation. We detect what we argue to be the obscured active nucleus with an effective angular resolution of 1dex) and therefore distort our view of high-redshift, gravitationally lensed galaxies.Department of HE and Training approved lis