4,901 research outputs found
Crystallization in a model glass: influence of the boundary conditions
Using molecular dynamics calculations and the Voronoi tessellation, we study
the evolution of the local structure of a soft-sphere glass versus temperature
starting from the liquid phase at different quenching rates. This study is done
for different sizes and for two different boundary conditions namely the usual
cubic periodic boundary conditions and the isotropic hyperspherical boundary
conditions for which the particles evolve on the surface of a hypersphere in
four dimensions. Our results show that for small system sizes, crystallization
can indeed be induced by the cubic boundary conditions. On the other hand we
show that finite size effects are more pronounced on the hypersphere and that
crystallization is artificially inhibited even for large system sizes.Comment: 11 pages, 2 figure
The lives of FR I radio galaxies
After a brief introduction to the morphological properties of FRI radio
sources, we discuss the possibility that FRI jets are relativistic at their
bases and decelerate quickly to non-relativistic velocities. From two-frequency
data we determine spectral index distributions and consequently the ages of FRI
sources. We show that in the large majority of cases synchrotron theory
provides unambiguous and plausible answers; in a few objects re-acceleration of
electrons may be needed. The derived ages are of the order 10^7-10^8 years, 2-4
times larger than the ages inferred from dynamical arguments and a factor 5-10
larger than the ages of FRII sources. The linear sizes of FRI and FRII sources
make it unlikely that many FRII's evolve into FRI's. A brief discussion is
given of the possibility that radio sources go through different cycles of
activity.Comment: 19 pages, including 13 figures, to appear in `Life Cycles of Radio
Galaxies', ed. J. Biretta et al., New Astronomy Review
A Parsec Scale Accelerating Radio Jet in the Giant Radio Galaxy NGC315
Observations of the core of the giant radio galaxy NGC315 made with VLBI
interferometers are discussed in the context of a relativistic jet. The
sidedness asymmetry suggests Doppler favoritism from a relativistic jet. The
presence of moving features in the jet as well as jet counter--jet brightness
ratios hint at an accelerating, relativistic jet. An increasing jet velocity is
also supported by a comparison of the jet's observed properties with the
predictions of an adiabatic expansion model. On the parsec scale, the jet is
unpolarized at a wavelength of 6 cm to a very high degree in clear distinction
to the high polarization seen on the kiloparsec scale.Comment: 24 pages with 8 figures. ApJ in pres
HST\/NICMOS observations of the host galaxies of powerful radio sources: Does size matter?
We present near-infrared J and K band imaging of a sample of powerful radio source host galaxies with the Hubble Space Telescope NICMOS2 camera. These sources have been selected on their double lobed radio structure, and include a wide range of projected radio source sizes. The largest projected linear sizes range from the compact Gigahertz Peaked Spectrum (GPS, 20 kpc) classical doubles (FR II radio sources). We investigate the dependence of host galaxy properties (including near-IR surface brightness profiles) on radio source size, using both our own and published data. The absolute magnitudes and surface brightness profiles are consistent with the host galaxies being regular giant elliptical galaxies rather than Brightest Cluster Galaxies (BCGs). We find that the GPS, CSS, and FR II host galaxies are a uniform class of objects, consistent with a scenario in which a powerful radio source evolves along this size sequence
Multifrequency Study of The Radio Galaxy NGC326
We present the results of a multi-frequency study of the inversion symmetric
radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8,
8.5 and 14.9 GHz. The morphological, spectral and polarization properties of
this peculiar object are studied at different levels of spatial resolutions.
The interpretation of the data will be discussed in forthcoming papers.Comment: 15 pages, 15 ps figures, accepted by A&
X-ray-emitting Atmospheres of B2 Radio Galaxies
We report ROSAT PSPC spatial and spectral analysis of the eight B2 radio
galaxies NGC 315, NGC 326, 4C 35.03, B2 0326+39, NGC 2484, B2 1040+31, B2
1855+37, and 3C 449, expected to be representative of the class of low-power
radio galaxies. Multiple X-ray components are present in each, and the gas
components have a wide range of linear sizes and follow an extrapolation of the
cluster X-ray luminosity/temperature correlation, implying that there is no
relationship between the presence of a radio galaxy and the gas fraction of the
environment. No large-scale cooling flows are found. There is no correlation of
radio-galaxy size with the scale or density of the X-ray atmosphere. This
suggests that it is processes on scales less than those of the overall gaseous
environments which are the major influence on radio-source dynamics. The
intergalactic medium is usually sufficient to confine the outer parts of the
radio structures, in some cases even to within 5 kpc of the core. In the case
of NGC 315, an extrapolation suggests that the pressure of the atmosphere may
match the minimum pressure in the radio source over a factor of about 40 in
linear size (a factor of about 1600 in pressure).Comment: 34 pages, including 10 figures, using aasms4.sty To appear in the Ap
A Search for Molecular Gas in GHz Peaked Spectrum Radio Sources
We present searches for molecular gas (CO, OH, CS, and Ammonia) in six GHz
Peaked Spectrum (GPS) radio sources. We do not detect gas in any source and
place upper limits on the mass of molecular gas which are generally in the
range 1E9 to a few times 1E10 solar masses. These limits are consistent with
the following interpretations: (1) GPS sources do not require very dense gas in
their hosts, and (2) The GPS sources are unlikely to be confined by dense gas
and will evolve to become larger radio sources
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