Large-Scale Structures Behind the Milky Way from Near-IR Surveys

About 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various approaches are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We investigated the potential of using the DENIS NIR survey for studies of galaxies behind the obscuration layer of our Milky Way and for mapping the Galactic extinction. As a pilot study, we recovered DENIS I, J and K band images of heavily obscured but optically still visible galaxies. We determined the I, J and K band luminosity functions of galaxies on three DENIS strips that cross the center of the nearby, low-latitude, rich cluster Abell 3627. The extinction-corrected I-J and J-K colours of these cluster galaxies compare well with that of an unobscured cluster. We searched for and identified galaxies at latitudes where the Milky Way remains fully opaque (|b| 4-5mag) - in a systematic search as well as around positions of galaxies detected with the blind HI survey of the ZOA currently conducted with the Multibeam Receiver of the Parkes Radiotelescope.Comment: 12 pages, including 5 PS figures, LaTeX, uses crckapb.sty and epsf.tex. Better resolved figures available upon request. To appear in proceedings of the 3rd Euroconference (Meudon, France, June 1997) on ``The Impact of Near IR Surveys'', Kluwer 199

SN 1986J VLBI. The Evolution and Deceleration of the Complex Source and a Search for a Pulsar Nebula

We report on VLBI observations of supernova 1986J in the spiral galaxy NGC 891 at two new epochs, 1990 July and 1999 February, t=7.4 and 15.9 yr after the explosion, and on a comprehensive analysis of these and earlier observations from t~4 yr after the explosion date, which we estimate to be 1983.2 +/- 1.1. The source is a shell or composite, and continues to show a complex morphology with large brightness modulations along the ridge and with protrusions. The supernova is moderately to strongly decelerated. The average outer radius expands as t^(0.71 +/- 0.11), and the expansion velocity has slowed to 6000 km/s at t=15.9 yr from an extrapolated 20,000 km/s at t=0.25 yr. The structure changes significantly with time, showing that the evolution is not self-similar. The shell structure is best visible at the latest epoch, when the protrusions have diminished somewhat in prominence and a new, compact component has appeared. The radio spectrum shows a clear inversion above 10 GHz. This might be related to a pulsar nebula becoming visible through the debris of the explosion. The radio flux density between 1.5 and 23 GHz decreases strongly with time, with the flux density proportional to t^(-2.94 +/- 0.24) between t~15 to 19 yr. This decrease is much more rapid than that found in earlier measurements up to t~6 yr.Comment: 24 pages, 9 Figures, LaTeX Accepted for Publication in the Astrophysical Journa

Non-linear Constrained Realizations of the Large Scale Structure

The linear algorithm of the Wiener filter and constrained realizations (CRs) of Gaussian random fields is extended here to perform non-linear CRs. The procedure consists of: (1) Using low resolution data to constrain a high resolution realization of the underlying field, as if the linear theory is valid; (2) Taking the linear CR backwards in time, by the linear theory, to set initial conditions for N-body simulations; (3) Forwarding the field in time by an N-body code. An intermediate step is introduced to `linearize' the low resolution data. The non-linear CR can be applied to any observational data set that is quasi-linearly related to the underlying field. Here it is applied to the IRAS 1.2Jy catalog using 846 data points within a sphere of 6000 km/s, to reconstruct the full non-linear large scale structure of our `local' universe. The method is tested against mock IRAS surveys, taken from random non-linear realizations. A detaile analysis of the reconstructed non-linear structure is presented.Comment: TeX file, 29 pages, 12 figures (included in the text), accepted in ApJ main journa

Galaxy Candidates in the Zone of Avoidance

Motivated by recent discoveries of nearby galaxies in the Zone of Avoidance, we conducted a pilot study of galaxy candidates at low Galactic latitude, near Galactic longitude $l \sim 135^0$, where the Supergalactic Plane is crossed by the Galactic Plane. We observed with the 1m Wise Observatory in the I-band 18 of the `promising' candidates identified by visual examination of Palomar red plates by Hau et al. (1995). A few candidates were also observed in R or B bands, or had spectroscopic observations performed at the Isaac Newton Telescope and at the Wise Observatory. Our study suggests that there are probably 10 galaxies in this sample. We also identify a probable Planetary Nebula. The final confirmation of the nature of these sources must await the availability of full spectroscopic information. The success rate of $\sim 50$ in identifying galaxies at Galactic latitude $|b|<5^\circ$ indicates that the ZOA is a bountiful region to discover new galaxies.Comment: 11 pages; Latex + 5 figures (gif format), Submitted to MNRA

Prevalence of Parental Thrombophilic Defects After Fetal Death and Relation to Cause

OBJECTIVE: To estimate whether parental thrombophilic defects after fetal death, either acquired or inherited, were more prevalent than in the normal population and to estimate associations between these thrombophilic defects and different fetal death causes. METHODS: In a multicenter, prospective cohort study of 750 fetal deaths, we tested couples for antithrombin, protein C, total and free protein S, and von Willebrand factor (vWF) plasma levels. Mothers' values were compared with reference values in gestational age-matched healthy pregnant women, and fathers were compared with healthy men. Prevalence of factor V Leiden, prothrombin G20210A mutation, and lupus anticoagulant were compared with the normal population. A panel classified death cause. RESULTS: More women with fetal death had decreased antithrombin (16.8%, P <.001) and protein C (4.0%, P = .03) and increased vWF (15.5%, P <.001) plasma levels than healthy pregnant women (2.5%). However, compared with normal ranges in the nonpregnant population, we only observed more women with increased vWF (12.4%, P <.001). More fathers had decreased free protein S (6.3%, P <.001) and elevated vWF (12.1%, P <.001) than healthy men (2.5%). Prevalence of inherited thrombophilias was not higher in couples with fetal death than in the population. Neither inherited nor acquired maternal or paternal thrombophilic defects were associated with the main cause of death. Of placental causes, abruption and infarction were associated with acquired maternal defects. CONCLUSION: Except for vWF and paternal free protein S, acquired and inherited thrombophilic defects were not more prevalent after fetal death. Routine thrombophilia testing after fetal death is not advised

Anomalous wave reflection from the interface of two strongly nonlinear granular media

Granular materials exhibit a strongly nonlinear behaviour affecting the propagation of information in the medium. Dynamically self-organized strongly nonlinear solitary waves are the main information carriers in granular chains. Here we report the first experimental observation of the dramatic change of reflectivity from the interface of two granular media triggered by a noncontact magnetically induced initial precompression. It may be appropriate to name this phenomenon the "acoustic diode" effect. Based on numerical simulations, we explain this effect by the high gradient of particle velocity near the interface.Comment: 14 pages, 3 figure

Survey of the ISM in Early-Type Galaxies. IV. The Hot Dust Component

We present mid-IR photometric properties for a sample of 28 early-type galaxies observed at 6.75, 9.63 and 15 um with the ISOCAM instrument on board the ISO satellite. We find total mid-IR luminosities in the range 3-48x10^8 L_sun. The spectral energy distribution (SED) of the galaxies were derived using the mid-IR data together with previously published UV, optical and near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated at T ~ 260 K. Dust grains properties are inferred from the mid-IR colors. The masses of the hot dust component are in the range 10-400 M_sun. The relationship between the masses derived from mid-IR observations and those derived from visual extinction are discussed. The possible common heating source for the gas and dust is investigated through the correlations between Ha and mid-IR luminosities.Comment: 10 pages, LaTeX (aa.cls), 11 figures (f. 2-4 are colour plates). Accepted for publication in Astronomy & Astrophysic

The Camassa-Holm equation as the long-wave limit of the improved Boussinesq equation and of a class of nonlocal wave equations

In the present study we prove rigorously that in the long-wave limit, the unidirectional solutions of a class of nonlocal wave equations to which the improved Boussinesq equation belongs are well approximated by the solutions of the Camassa-Holm equation over a long time scale. This general class of nonlocal wave equations model bidirectional wave propagation in a nonlocally and nonlinearly elastic medium whose constitutive equation is given by a convolution integral. To justify the Camassa-Holm approximation we show that approximation errors remain small over a long time interval. To be more precise, we obtain error estimates in terms of two independent, small, positive parameters $\epsilon$ and $\delta$ measuring the effect of nonlinearity and dispersion, respectively. We further show that similar conclusions are also valid for the lower order approximations: the Benjamin-Bona-Mahony approximation and the Korteweg-de Vries approximation.Comment: 24 pages, to appear in Discrete and Continuous Dynamical System

The optical polarization of the blazar PKS 2155–304 during an optical flare in 2010

An analysis is presented of the optical polarimetric and multicolour photometric (BVRJ) behaviour of the blazar PKS 2155–304 during an outburst in 2010. This flare develops over roughly 117 d, with a flux doubling time τ ∼ 11 d, which increases from blue to red wavelengths. The polarization angle is initially aligned with the jet axis but rotates by roughly 90° as the flare grows. Two distinct states are evident at low and high fluxes. Below 18 mJy, the polarization angle takes on a wide range of values, without any clear relation to the flux. In contrast, there is a positive correlation between the polarization angle and flux above 18 mJy