9,007 research outputs found
Is an obscured AGN at the centre of the disk galaxy IC 2497 responsible for Hanny's Voorwerp?
We present the results of VLBI and MERLIN observations of the massive disk
galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a
giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy.
Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact
radio component (C1) at the centre of IC 2497. The brightness temperature of C1
was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations
presented here, re-confirm the existence of C1 but also reveal the existence of
a second compact component (C2) located about 230 milliarcseconds to the
North-East of C1. The brightness temperature of C2 is measured to be greater
than 1.4E5 K, suggesting that both components may be related to AGN activity
(e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations
show both components. C1 is shown to be compact with a slight elongation along
the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in
an almost perpendicular direction to the direction of the Voorwerp. Our results
continue to support the hypothesis that IC 2497 contains an Active Galactic
Nucleus (AGN), and that a jet associated with this AGN clears a path that
permits ionising radiation from the AGN to directly illuminate the emission
nebula.Comment: Presented at The 8th International e-VLBI Workshop: the Science and
Technology of Long Baseline Real-Time Interferometry, EXPReS09, June 22-26
2009 Madrid, Spain. 5 pages, 5 article
Broad applications of diffusion bonding
Solid state joining of materials by diffusion bondin
WSRT 1.4 GHz Observations of the Hubble Deep Field
We present WSRT 1.38 GHz observations of the Hubble Deep Field (and flanking
fields). 72 hours of data were combined to produce the WSRT's deepest image
yet, achieving an r.m.s. noise level of 8 microJy per beam. We detect radio
emission from galaxies both in the HDF and HFF which have not been previously
detected by recent MERLIN or VLA studies of the field.Comment: 2 pages, 1 figure, to appear in "The Universe at Low Radio
Frequencies", IAU Symposium 199. For colour figures, see
http://www.nfra.nl/~mag/hdf_wsrt.htm
A Deep WSRT 1.4 GHz Radio Survey of the Spitzer Space Telescope FLSv Region
The First Look Survey (FLS) is the first scientific product to emerge from
the Spitzer Space Telescope. A small region of this field (the verification
strip) has been imaged very deeply, permitting the detection of cosmologically
distant sources. We present Westerbork Synthesis Radio Telescope (WSRT)
observations of this region, encompassing a ~1 sq. deg field, centred on the
verification strip (J2000 RA=17:17:00.00, DEC=59:45:00.000). The radio images
reach a noise level of ~ 8.5 microJy/beam - the deepest WSRT image made to
date. We summarise here the first results from the project, and present the
final mosaic image, together with a list of detected sources. The effect of
source confusion on the position, size and flux density of the faintest sources
in the source catalogue are also addressed. The results of a serendipitous
search for HI emission in the field are also presented. Using a subset of the
data, we clearly detect HI emission associated with four galaxies in the
central region of the FLSv. These are identified with nearby, massive galaxies.Comment: 9 pages, 6 figures (fig.3 in a separate gif file). Accepted for
publication in A&A. The full paper and the related material can be downloaded
from http://www.astron.nl/wsrt/WSRTsurveys/WFLS
Social and Economic Impact of Solar Electricity at Schuchuli Village
Schuchuli, a small remote village on the Papago Indian Reservation in southwest Arizona, is 27 kilometers (17 miles) from the nearest available utility power. Its lack of conventional power is due to the prohibitive cost of supplying a small electrical load with a long-distance distribution line. Furthermore, alternate energy sources are expensive and place a burden on the resources of the villagers. On December 16, 1978, as part of a federally funded project, a solar cell power system was put into operation at Schuchuli. The system powers the village water pump, lighting for homes and other village buildings, family refrigerators and a communal washing machine and sewing machine
Hamiltonian formalism and the Garrett-Munk spectrum of internal waves in the ocean
Wave turbulence formalism for long internal waves in a stratified fluid is
developed, based on a natural Hamiltonian description. A kinetic equation
appropriate for the description of spectral energy transfer is derived, and its
self-similar stationary solution corresponding to a direct cascade of energy
toward the short scales is found. This solution is very close to the high
wavenumber limit of the Garrett-Munk spectrum of long internal waves in the
ocean. In fact, a small modification of the Garrett-Munk formalism includes a
spectrum consistent with the one predicted by wave turbulence.Comment: 4 pages latex fil
The Lockman Hole Project: new constraints on the sub-mJy source counts from a wide-area 1.4 GHz mosaic
This paper is part of a series discussing the results obtained in the
framework of a wide international collaboration - the Lockman Hole Project -
aimed at improving the extensive multiband coverage available in the Lockman
Hole region, through novel deep, wide-area, multifrequency (60, 150, 350 MHz,
and 1.4 GHz) radio surveys. This multifrequency, multi-band information will be
exploited to get a comprehensive view of star formation and active galactic
nucleus activities in the high-redshift Universe from a radio perspective. In
this paper, we present novel 1.4 GHz mosaic observations obtained with the
Westerbork Synthesis Radio Telescope. With an area coverage of 6.6 deg2, this
is the largest survey reaching an rms noise of 11 uJy/beam. In this paper, we
present the source catalogue (~6000 sources with flux densities S>55 uJy
(5sigma), and we discuss the 1.4 GHz source counts derived from it. Our source
counts provide very robust statistics in the flux range 0.1<S<1 mJy, and are in
excellent agreement with other robust determinations obtained at lower and
higher flux densities. A clear excess is found with respect to the counts
predicted by the semi-empirical radio sky simulations developed in the
framework of the Square Kilometre Array Simulated Skies project. A preliminary
analysis of the identified (and classified) sources suggests this excess is to
be ascribed to star-forming galaxies, which seem to show a steeper evolution
than predicted.Comment: accepted for publication on MNRAS. New version that corrects latex
errors and contain the correct version of figure 1
Bound states of magnons in the S=1/2 quantum spin ladder
We study the excitation spectrum of the two-leg antiferromagnetic S=1/2
Heisenberg ladder. Our approach is based on the description of the excitations
as triplets above a strong-coupling singlet ground state. The quasiparticle
spectrum is calculated by treating the excitations as a dilute Bose gas with
infinite on-site repulsion. We find singlet (S=0) and triplet (S=1)
two-particle bound states of the elementary triplets. We argue that bound
states generally exist in any dimerized quantum spin model.Comment: 4 REVTeX pages, 4 Postscript figure
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