An Anomalous UV Extension in NGC6251

Deep U-band FOC images of the nuclear region of NGC6251 have revealed a region of extended emission which is most probably radiation scattered from a continuum source in the nucleus. This radiation lies interior to a dust ring, is nearly perpendicular to the radio jet axis, and is seen primarily in the FOC U and b filters. The extension has a low observed polarization($\le 10$), and is unlikely to arise from line emission. We know of no other examples similar to what we have found in NGC 6251, and we offer some tentative explanations. The nuclear morphology shows clear similarities to that seen in the nucleus of NGC 4261 except for the extended U-band radiation.Comment: 14 pages AAStex format + 4 figures; accepted for publication in ApJ Letter

Measurement of macroscopic plasma parameters with a radio experiment: Interpretation of the quasi-thermal noise spectrum observed in the solar wind

The ISEE-3 SBH radio receiver has provided the first systematic observations of the quasi-thermal (plasma waves) noise in the solar wind plasma. The theoretical interpretation of that noise involves the particle distribution function so that electric noise measurements with long antennas provide a fast and independent method of measuring plasma parameters: densities and temperatures of a two component (core and halo) electron distribution function have been obtained in that way. The polarization of that noise is frequency dependent and sensitive to the drift velocity of the electron population. Below the plasma frequency, there is evidence of a weak noise spectrum with spectral index -1 which is not yet accounted for by the theory. The theoretical treatment of the noise associated with the low energy (thermal) proton population shows that the moving electrical antenna radiates in the surrounding plasma by Carenkov emission which becomes predominant at the low frequencies, below about 0.1 F sub P

Estimation des formes du phosphore dans la rivière Venoge en crue

Des échantillons d'eau de rivière ont été prélevés près de l'embouchure de la Venoge, affluent du Léman, au cours de cinq crues survenues entre octobre 1986 et novembre 1987. Les échantillons ont été extraits de grands volumes d'eau à l'aide d'une centrifugeuse à débit continu. La concentration de matières en suspension, et les formes du phosphore de ces échantillons ont été dosés. L'interprétation de ces données, basée sur une méthode de régression progressive, montre que la concentration en phosphore particulaire total peut être estimée par deux paramètres, la fraction de suspensions supérieure à 63 µm et la concentration en phosphore réactif dissous. Par ailleurs, puisqu'il existe des relations statistiques entre le phosphore particulaire total et les autres formes du phosphore particulaire, il est possible d'évaluer la concentration de ces dernières (formes de phosphore apatitique, non apatitique, organique et inorganique). Le phosphore total dissous peut être pareillement estimé en fonction du phosphore réactif dissous. L'estimation des formes du phosphore et ainsi que celle de leur charge en crue peut donc se faire même lorsque le volume des échantillons est limité, c'est-à-dire, lorsque la quantité de matières en suspension n'est pas suffisante pour l'analyse de toutes les formes du phosphore particutaire.In order to gain a better understanding of phosphorus transport in a storm-dependent river system, water samples were collected near the mouth of the River Venoge, Switzerlang, during five storm events between october 1986 and november 1987. Suspended sediment (SS) was extracted from large-volume water samples by continuous flow centrifugation. Soluble and particulate forms of phosphorus were subsequently analysed with the centrifuged and filtered (0.45 µm) waters, and freeze-dried SS in a < 63 µm fraction.However, the sampling usually performed at more than 4-hour intervals could not guarantee that no information had been missed, for example, the instantaneous fluctuation of soluble reactive phosphorus (SRP) during the events. Although more frequent sampling using an auto-sampler is feasible, the small volume of raw water cannot provide sufficient sediment for all the analyses of phosphorus forms. Thus, it would be useful to find a model capable of estimating phosphorus concentration in different forms, whenever the present measurements are not possible.A multivariate progressive analysis of the measured phosphorus data set shows that total particulate phosphorus (TPP) concentration can be estimated as a function of two parameters, the percentage of a SS fraction coarser than 63 µm and the SRP concentration measured in filtered water. On the other hand, general statistical relationships exist between the various forms of phosphorus. Total soluble phosphorus (TSP) is dependent upon SRP. Organic phosphorus (OP) and non-apatite inorganic phosphorus (NAIP) can be approximately assessed from TPP, measured or calculated. Then, apatite phosphorus (AP), inorganic phosphorus (IP) and total phosphorus in raw water can be calculated by means of summation/substraction operations.Modelling is apparently suitable to the storm events during which only a limited volume of water samples could be collected. It also provides a rapid way to estimate the partitioning of phosphorus loads in high flow periods of the river system, thereby reducing the field and laboratory work required

Dust detection by the wave instrument on STEREO: nanoparticles picked up by the solar wind?

The STEREO/WAVES instrument has detected a very large number of intense voltage pulses. We suggest that these events are produced by impact ionisation of nanoparticles striking the spacecraft at a velocity of the order of magnitude of the solar wind speed. Nanoparticles, which are half-way between micron-sized dust and atomic ions, have such a large charge-to-mass ratio that the electric field induced by the solar wind magnetic field accelerates them very efficiently. Since the voltage produced by dust impacts increases very fast with speed, such nanoparticles produce signals as high as do much larger grains of smaller speeds. The flux of 10-nm radius grains inferred in this way is compatible with the interplanetary dust flux model. The present results may represent the first detection of fast nanoparticles in interplanetary space near Earth orbit.Comment: In press in Solar Physics, 13 pages, 5 figure

Prospects for strangeness measurement in ALICE

The study of strangeness production at LHC will bring significant information on the bulk chemical properties, its dynamics and the hadronisation mechanisms involved at these energies. The ALICE experiment will measure strange particles from topology (secondary vertices) and from resonance decays over a wide range in transverse momentum and shed light on this new QCD regime. These motivations will be presented as well as the identification performance of ALICE for strange hadrons.Comment: 12 pages, 11 figures Proceedings of the Workshop on Relativistic Nuclear Physics (WRNP) 2007, Kiev, Ukraine Conference Info: http://wrnp2007.bitp.kiev.ua/ Submitted to "Physics of Atomic Nuclei

Spacecraft charging and ion wake formation in the near-Sun environment

A three-dimensional (3-D), self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characteristic energy of the escaping photoelectrons. All of these conditions are present near the Sun. The numerical solutions also show that the spacecraft's negative potential can be amplified by an ion wake. The negative potential of the ion wake prevents secondary electrons from escaping the part of spacecraft in contact with the wake. These findings may be important for future spacecraft missions that go nearer to the Sun, such as Solar Orbiter and Solar Probe Plus.Comment: 25 pages, 7 figures, accepted for publication in Physics of Plasma

Are we seeing accretion flows in a 250kpc-sized Ly-alpha halo at z=3?

Using MUSE on the ESO-VLT, we obtained a 4 hour exposure of the z=3.12 radio galaxy MRC0316-257. We detect features down to ~10^-19 erg/s/cm^2/arcsec^2 with the highest surface brightness regions reaching more than a factor of 100 higher. We find Ly-alpha emission out to ~250 kpc in projection from the active galactic nucleus (AGN). The emission shows arc-like morphologies arising at 150-250 kpc from the nucleus in projection with the connected filamentary structures reaching down into the circum-nuclear region. The most distant arc is offset by 700 km/s relative to circum-nuclear HeII 1640 emission, which we assume to be at the systemic velocity. As we probe emission closer to the nucleus, the filamentary emission narrows in projection on the sky, the relative velocity decreases to ~250 km/s, and line full-width at half maximum range from 300-700 km/s. From UV line ratios, the emission on scales of 10s of kpc from the nucleus along a wide angle in the direction of the radio jets is clearly excited by the radio jets and ionizing radiation of the AGN. Assuming ionization equilibrium, the more extended emission outside of the axis of the jet direction would require 100% or more illumination to explain the observed surface brightness. High speed (>300 km/s) shocks into rare gas would provide sufficiently high surface brightness. We discuss the possibility that the arcs of Ly-alpha emission represent accretion shocks and the filamentary emission represent gas flows into the halo, and compare our results with gas accretion simulations.Comment: 4 pages, 2 figures, 1 table, A&A letters accepte

The MUSE 3D view of feedback in a high-metallicity radio galaxy at z = 2.9

We present a detailed study of the kinematic, chemical and excitation properties of the giant Ly$\alpha$ emitting nebula and the giant \ion{H}{I} absorber associated with the $z = 2.92$ radio galaxy MRC 0943--242, using spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments. Together, these data provide a wide range of rest-frame wavelength (765 \AA$\,$ -- 6378 \AA$\,$ at $z = 2.92$) and 2D spatial information. We find clear evidence for jet gas interactions affecting the kinematic properties of the nebula, with evidence for both outflows and inflows being induced by radio-mode feedback. We suggest that the regions of relatively lower ionization level, spatially correlated with the radio hotspots, may be due to localised compression of photoionized gas by the expanding radio source, thereby lowering the ionization parameter, or due to a contribution from shock-heating. We find that photoionization of super-solar metallicity gas ($Z/Z_{\odot}$ = 2.1) by an AGN-like continuum ($\alpha$=--1.0) at a moderate ionization parameter ($U$ = 0.018) gives the best overall fit to the complete X-SHOOTER emission line spectrum. We identify a strong degeneracy between column density and Doppler parameter such that it is possible to obtain a reasonable fit to the \ion{H}{I} absorption feature across the range log N(\ion{H}{I}/cm$^{-2}$) = 15.20 and 19.63, with the two best-fitting occurring near the extreme ends of this range. The extended \ion{H}{I} absorber is blueshifted relative to the emission line gas, but shows a systematic decrease in blueshift towards larger radii, consistent with a large scale expanding shell.Comment: 25 pages, 18 figures, 10 tables. Accepted for publication in MNRAS. Published: 23 November 201

Galaxy protocluster candidates around z ~ 2.4 radio galaxies

We study the environments of 6 radio galaxies at 2.2 < z < 2.6 using wide-field near-infrared images. We use colour cuts to identify galaxies in this redshift range, and find that three of the radio galaxies are surrounded by significant surface overdensities of such galaxies. The excess galaxies that comprise these overdensities are strongly clustered, suggesting they are physically associated. The colour distribution of the galaxies responsible for the overdensity are consistent with those of galaxies that lie within a narrow redshift range at z ~ 2.4. Thus the excess galaxies are consistent with being companions of the radio galaxies. The overdensities have estimated masses in excess of 10^14 solar masses, and are dense enough to collapse into virizalised structures by the present day: these structures may evolve into groups or clusters of galaxies. A flux-limited sample of protocluster galaxies with K < 20.6 mag is derived by statistically subtracting the fore- and background galaxies. The colour distribution of the protocluster galaxies is bimodal, consisting of a dominant blue sequence, comprising 77 +/- 10% of the galaxies, and a poorly populated red sequence. The blue protocluster galaxies have similar colours to local star-forming irregular galaxies (U -V ~ 0.6), suggesting most protocluster galaxies are still forming stars at the observed epoch. The blue colours and lack of a dominant protocluster red sequence implies that these cluster galaxies form the bulk of their stars at z < 3.Comment: Accepted for publication in MNRA