707 research outputs found
Asia Rising: Ships of State?
The commercial-strategic linkages and state support for PRC port and shipping ventures resemble a twenty-first-century version of the Dutch East India Company. These notionally commercial enterprises operate globally with the full financial and military backing of their home state, and the vessels that connect the ports are “ships of state,” functioning as instruments of Chinese national strategy while they sail as commercial carriers
Far Ultraviolet Emission in the A2597 and A2204 Brightest Cluster Galaxies
We use the Hubble Space Telescope ACS/SBC and Very Large Telescope FORS
cameras to observe the Brightest Cluster Galaxies in Abell 2597 and Abell 2204
in the far-ultraviolet (FUV) F150LP and optical U, B, V, R, I Bessel filters.
The FUV and U band emission is enhanced in bright, filamentary structures
surrounding the BCG nuclei. These filaments can be traced out to 20 kpc from
the nuclei in the FUV. Excess FUV and U band light is determined by removing
emission due to the underlying old stellar population and mapped with 1 arcsec
spatial resolution over the central 20 kpc regions of both galaxies. We find
the FUV and U excess emission to be spatially coincident and a stellar
interpretation requires the existence of a significant amount of 10000-50000 K
stars. Correcting for nebular continuum emission and dust intrinsic to the BCG
further increases the FUV to U band emission ratio and implies that stars alone
may not suffice to explain the observations. However, lack of detailed
information on the gas and dust distribution and extinction law in these
systems prevents us from ruling out a purely stellar origin. Non-stellar
processes, such as the central AGN, Scattering, Synchrotron and Bremsstrahlung
emission are investigated and found to not be able to explain the FUV and U
band measurements in A2597. Contributions from non-thermal processes not
treated here should be investigated. Comparing the FUV emission to the optical
H-alpha line emitting nebula shows good agreement on kpc-scales in both A2597
and A2204. In concordance with an earlier investigation by O'Dea et al. (2004)
we find that O-stars can account for the ionising photons necessary to explain
the observed H-alpha line emission.Comment: accepted by mnra
The Distribution and Condition of the Warm Molecular Gas in Abell 2597 and Sersic 159-03
We have used the SINFONI integral field spectrograph to map the near-infrared
K-band emission lines of molecular and ionised hydrogen in the central regions
of two cool core galaxy clusters, Abell 2597 and Sersic 159-03. Gas is detected
out to 20 kpc from the nuclei of the brightest cluster galaxies and found to be
distributed in clumps and filaments around it. The ionised and molecular gas
phases trace each other closely in extent and dynamical state. Both gas phases
show signs of interaction with the active nucleus. Within the nuclear regions
the kinetic luminosity of this gas is found to be somewhat smaller than the
current radio luminosity. Outside the nuclear region the gas has a low velocity
dispersion and shows smooth velocity gradients. There is no strong correlation
between the intensity of the molecular and ionised gas emission and either the
radio or X-ray emission. The molecular gas in Abell 2597 and Sersic 159-03 is
well described by a gas in local thermal equilibrium (LTE) with a single
excitation temperature T_exc ~ 2300 K. The emission line ratios do not vary
strongly as function of position, with the exception of the nuclear regions
where the ionised to molecular gas ratio is found decrease. These constant line
ratios imply a single source of heating and excitation for both gas phases.Comment: 44 pages, 32 figures, accepted for publication in MNRA
Radio Emission from GRO J1655-40 during the 1994 Jet Ejection Episodes
We report multifrequency radio observations of GRO J1655-40 obtained with the
Australia Telescope Compact Array, the Molonglo Observatory Synthesis Telescope
and the Hartebeesthoek Radio Astronomy Observatory at the time of the major
hard X-ray and radio outbursts in 1994 August-September. The radio emission
reached levels of the order of a few Jy and was found to be linearly polarized
by up to 10%, indicating a synchrotron origin. The light curves are in good
agreement with those measured with the VLA, but our closer time sampling has
revealed two new short-lived events and significant deviations from a simple
exponential decay. The polarization data show that the magnetic field is well
ordered and aligned at right angles to the radio jets for most of the
monitoring period. The time evolution of the polarization cannot be explained
solely in terms of a simple synchrotron bubble model, and we invoke a hybrid
`core-lobe' model with a core which contributes both synchrotron and free-free
emission and `lobes' which are classical synchrotron emitters.Comment: 36 pages, 5 tables, 9 figures; accepted for publication in Ap
Searching (the) FIRST radio arcs near ACO clusters
Gravitational lensing (GL) of distant radio sources by galaxy clusters should
produce radio arc(let)s. We extracted radio sources from the FIRST survey near
Abell cluster cores and found their radio position angles to be uniformly
distributed with respect to the cluster centres. This result holds even when we
restrict the sample to the richest or most centrally condensed clusters, and to
sources with high S/N and large axial ratio. Our failure to detect GL with
statistical methods may be due to poor cluster centre positions. We did not
find convincing candidates for arcs either. Our result agrees with theoretical
estimates predicting that surveys much deeper than FIRST are required to detect
the effect. This is in apparent conflict with the detection of such an effect
claimed by Bagchi & Kapahi (1995).Comment: 6 pages; 8 figures and 1 style file are included; to appear in Proc.
"Observational Cosmology with the New Radio Surveys", eds. M. Bremer, N.
Jackson & I. Perez-Fournon, Kluwer Acad. Pres
A View through Faraday's Fog 2: Parsec Scale Rotation Measures in 40 AGN
Results from a survey of the parsec scale Faraday rotation measure properties
for 40 quasars, radio galaxies and BL Lac objects are presented. Core rotation
measures for quasars vary from approximately 500 to several thousand radians
per meter squared. Quasar jets have rotation measures which are typically 500
radians per meter squared or less. The cores and jets of the BL Lac objects
have rotation measures similar to those found in quasar jets. The jets of radio
galaxies exhibit a range of rotation measures from a few hundred radians per
meter squared to almost 10,000 radians per meter squared for the jet of M87.
Radio galaxy cores are generally depolarized, and only one of four radio
galaxies (3C-120) has a detectable rotation measure in the core. Several
potential identities for the foreground Faraday screen are considered and we
believe the most promising candidate for all the AGN types considered is a
screen in close proximity to the jet. This constrains the path length to
approximately 10 parsecs, and magnetic field strengths of approximately 1
microGauss can account for the observed rotation measures. For 27 out of 34
quasars and BL Lacs their optically thick cores have good agreement to a lambda
squared law. This requires the different tau = 1 surfaces to have the same
intrinsic polarization angle independent of frequency and distance from the
black hole.Comment: Accepted to the Astrophysical Journal: 71 pages, 40 figure
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
In order to identify the dominant nuclear outflow mechanisms in Active
Galactic Nuclei, we have undertaken deep, high resolution observations of two
compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera
for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets
known to have powerful emission line outflows, but they also contain all the
potential drivers for the outflows: relativistic jets, quasar nuclei and
starbursts. ACS allows the compact nature (<0.15") of these radio sources to be
optically resolved for the first time. Through comparison with existing radio
maps we have seen consistency in the nuclear position angles of both the
optical emission line and radio data. There is no evidence for bi-conical
emission line features on the large-scale and there is a divergance in the
relative position angles of the optical and radio structure. This enables us to
exclude starburst driven outflows. However, we are unable to clearly
distinguish between radiative AGN wind driven outflows and outflows powered by
relativistic radio jets. The small scale bi-conical features, indicative of
such mechanisms could be below the resolution limit of ACS, especially if
aligned close to the line of sight. In addition, there may be offsets between
the radio and optical nuclei induced by heavy dust obscuration, nebular
continuum or scattered light from the AGN.Comment: 9 pages, 8 figures, emulateapj, ApJ Accepte
STIS spectroscopy of the emission line gas in the nuclei of nearby FR-I galaxies
We present the results of the analysis of a set of medium resolution spectra,
obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space
Telescope, of the emission line gas present in the nuclei of a complete sample
of 21 nearby, early-type galaxies with radio jets (the UGC FR-I Sample). For
each galaxy nucleus we present spectroscopic data in the region of H-alpha and
the dervived kinematics.
We find that in 67% of the nuclei the gas appears to be rotating and, with
one exception, the cases where rotation is not seen are either face on or have
complex central morphologies. We find that in 62% of the nuclei the fit to the
central spectrum is improved by the inclusion of a broad component. The broad
components have a mean velocity dispersion of 1349 +/- 345 km\s and are
redshifted from the narrow line components (assuming an origin in H-alpha) by
486 +/- 443 km\s.Comment: 119 pages, 26 figures, ApJS Accepted, version with full figures
available at http://www.astro.columbia.edu/~jake/pub/fr1datapaper.pd
Ocean warming, not acidification, controlled coccolithophore response during past greenhouse climate change
Current carbon dioxide emissions are an assumed threat to oceanic calcifying plankton (coccolithophores) not just due to rising sea-surface temperatures, but also because of ocean acidification (OA). This assessment is based on single species culture experiments that are now revealing complex, synergistic, and adaptive responses to such environmental change. Despite this complexity, there is still a widespread perception that coccolithophore calcification will be inhibited by OA. These plankton have an excellent fossil record, and so we can test for the impact of OA during geological carbon cycle events, providing the added advantages of exploring entire communities across real-world major climate perturbation and recovery. Here we target fossil coccolithophore groups (holococcoliths and braarudosphaerids) expected to exhibit greatest sensitivity to acidification because of their reliance on extracellular calcification. Across the Paleocene-Eocene Thermal Maximum (56 Ma) rapid warming event, the biogeography and abundance of these extracellular calcifiers shifted dramatically, disappearing entirely from low latitudes to become limited to cooler, lower saturation-state areas. By comparing these range shift data with the environmental parameters from an Earth system model, we show that the principal control on these range retractions was temperature, with survival maintained in high-latitude refugia, despite more adverse ocean chemistry conditions. Deleterious effects of OA were only evidenced when twinned with elevated temperatures
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