Mass-to-light ratios of ellipticals in LCDM

We use the mass-to-light gradients in early-type galaxies to infer the global dark matter fraction, f_d=M_d/M_*, for these systems. We discuss implications about the total star formation efficiency in dark-matter halos and show that the trend of $f_{\rm d}$ with mass produces virial mass-to-light ratios which are consistent with semi-analitical models. Preliminary kurtosis analysis of the quasi-constant M/L galaxies in Romanowsky et al. seems at odd with Dekel et al. simulations.Comment: 5 pages, 4 figures. To appear in Proceedings of XXIst IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris, 4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP Sciences). Figure enlarged with respect the proceeding format, minor changes. Collaboration website at http://www.astro.rug.nl/~pns/pns_team.htm

Fluctuation characteristics of the TCV snowflake divertor measured with high speed visible imaging

Tangentially viewing fast camera footage of the low-field side snowflake minus divertor in TCV is analysed across a four point scan in which the proximity of the two X-points is varied systematically. The motion of structures observed in the post- processed movie shows two distinct regions of the camera frame exhibiting differing patterns. One type of motion in the outer scrape-off layer remains present throughout the scan whilst the other, apparent in the inner scrape-off layer between the two nulls, becomes increasingly significant as the X-points contract towards one another. The spatial structure of the fluctuations in both regions is shown to conform to the equilibrium magnetic field. When the X-point gap is wide the fluctuations measured in the region between the X-points show a similar structure to the fluctuations observed above the null region, remaining coherent for multiple toroidal turns of the magnetic field and indicating a physical connectivity of the fluctuations between the upstream and downstream regions. When the X-point gap is small the fluctuations in the inner scrape-off layer between the nulls are decorrelated from fluctuations upstream, indicating local production of filamentary structures. The motion of filaments in the inter-null region differs, with filaments showing a dominantly poloidal motion along magnetic flux surfaces when the X-point gap is large, compared to a dominantly radial motion across flux-surfaces when the gap is small. This demonstrates an enhancement to cross-field tranport between the nulls of the TCV low-field-side snowflake minus when the gap between the nulls is small.Comment: Accepted for publication in Plasma Physics and Controlled Fusio

Upper limits on neutrino masses from the 2dFGRS and WMAP: the role of priors

Solar, atmospheric, and reactor neutrino experiments have confirmed neutrino oscillations, implying that neutrinos have non-zero mass, but without pinning down their absolute masses. While it is established that the effect of neutrinos on the evolution of cosmic structure is small, the upper limits derived from large-scale structure data could help significantly to constrain the absolute scale of the neutrino masses. In a recent paper the 2dF Galaxy Redshift Survey (2dFGRS) team provided an upper limit m_nu,tot < 2.2 eV, i.e. approximately 0.7 eV for each of the three neutrino flavours, or phrased in terms of their contributioin to the matter density, Omega_nu/Omega_m < 0.16. Here we discuss this analysis in greater detail, considering issues of assumed 'priors' like the matter density Omega_m and the bias of the galaxy distribution with respect the dark matter distribution. As the suppression of the power spectrum depends on the ratio Omega_nu/Omega_m, we find that the out-of- fashion Mixed Dark Matter Model, with Omega_nu=0.2, Omega_m=1 and no cosmological constant, fits the 2dFGRS power spectrum and the CMB data reasonably well, but only for a Hubble constant H_0<50 km/s/Mpc. As a consequence, excluding low values of the Hubble constant, e.g. with the HST Key Project is important in order to get a strong constraint on the neutrino masses. We also comment on the improved limit by the WMAP team, and point out that the main neutrino signature comes from the 2dFGRS and the Lyman alpha forest.Comment: 24 pages, 12 figures Minor changes to matched version published in JCA

The Venus ionosphere in the northern polar region

PLASLIFE is a computer simulation which assists in the interpretation of high latitude ionospheric observations and, in this study, is applied to the polar regions of Venus. The Venus Express spacecraft samples the high latitude ionosphere in the northern hemisphere of the planet. On 4 August 2008 it was inserted into a new orbit with pericentre located below 200 km close to 86° N. The ASPERA-4 instrument on the spacecraft records the first extended in situ data set of the plasma environment in this sector. The observed ionospheric ion and electron populations exhibit significant variation between orbits and, by compensating for the effects of solar zenith angle and altitude, the relative contributions of photoionisation and plasma transport can be investigated. These variations are discussed with respect to parameters including local time and solar flux. Comparisons are drawn with the terrestrial ionosphere

Testing homogeneity with galaxy number counts : light-cone metric and general low-redshift expansion for a central observer in a matter dominated isotropic universe without cosmological constant

As an alternative to dark energy it has been suggested that we may be at the center of an inhomogeneous isotropic universe described by a Lemaitre-Tolman-Bondi (LTB) solution of Einstein's field equations. In order to test this hypothesis we calculate the general analytical formula to fifth order for the redshift spherical shell mass. Using the same analytical method we write the metric in the light-cone by introducing a gauge invariant quantity $G(z)$ which together with the luminosity distance $D_L(z)$ completely determine the light-cone geometry of a LTB model.Comment: 13 page

Construction of probabilistic event trees for eruption forecasting at Sinabung volcano, Indonesia 2013-14

Eruptions of Sinabung volcano, Indonesia have been ongoing since 2013. Since that time, the character of eruptions has changed, from phreatic to phreatomagmatic to magmatic explosive eruptions, and from production of a lava dome that collapsed to a subsequent thick lava flow that slowly ceased to be active, and later, to a new lava dome. As the eruption progressed, event trees were constructed to forecast eruptive behavior six times, with forecast windows that ranged from 2. weeks to 1. year: November 7-10, December 12-14, and December 27, 2013; and January 9-10, May 13, and October 7, 2014. These event trees were successful in helping to frame the forecast scenarios, to collate current monitoring information, and to document outstanding questions and unknowns. The highest probability forecasts closely matched outcomes of eruption size (including extrusion of the first dome), production of pyroclastic density currents, and pyroclastic density current runout distances. Events assigned low probabilities also occurred, including total collapse of the lava dome in January 2014 and production of a small blast pyroclastic density current in February 2014