723 research outputs found
Radio Continuum Jet in NGC 7479
The barred galaxy NGC 7479 hosts a remarkable jet-like radio continuum
feature: bright, 12-kpc long in projection, and hosting an aligned magnetic
field. The degree of polarization is 6%-8% along the jet, and remarkably
constant, which is consistent with helical field models. The radio brightness
of the jet suggests strong interaction with the ISM and hence a location near
the disk plane. We observed NGC 7479 at four wavelengths with the VLA and
Effelsberg radio telescopes. The equipartition strength is 35-40 micro-G for
the total and >10 micro-G for the ordered magnetic field in the jet. The jet
acts as a bright, polarized background. Faraday rotation between 3.5 and 6 cm
and depolarization between 6 and 22 cm can be explained by magneto-ionic gas in
front of the jet, with thermal electron densities of ~0.06 cm**(-3) in the bar
and ~0.03 cm**(-3) outside the bar. The regular magnetic field along the bar
points toward the nucleus on both sides. The regular field in the disk reveals
multiple reversals, probably consisting of field loops stretched by a shearing
gas flow in the bar. The projection of the jet bending in the sky plane is in
the sense opposite to that of the underlying stellar and gaseous spiral
structure. The bending in 3-D is most easily explained as a precessing jet,
with an age less than 10**6 years. Our observations are consistent with very
recent triggering, possibly by a minor merger. NGC 7479 provides a unique
opportunity to study interaction-triggered 15-kpc scale radio jets within a
spiral galaxy.Comment: 18 pages, 21 figures, accepted for publication in the Astrophysical
Journa
Large-Scale CO Maps of the Lupus Molecular Cloud Complex
Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward
three members of the Lupus Molecular Cloud Complex - Lupus I, III, and IV -
trace the column density and temperature of the molecular gas. Comparison with
IR extinction maps from the c2d project requires most of the gas to have a
temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are
roughly consistent with most previous estimates, while the line widths are
higher, around 2 km/s. CO 4-3 emission is found throughout Lupus I, indicating
widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the
NW end and along the edge of the B228 ridge in Lupus I, and a coherent velocity
gradient across the ridge, are consistent with interaction between the
molecular cloud and an expanding HI shell from the Upper-Scorpius subgroup of
the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be
stars, and shows no sign of external influence. Slightly warmer gas around the
core of Lupus IV and a low line width suggest heating by the
Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an HI shell.Comment: 54 pages, 27 figures, 5 tables. To appear in ApJS. Preprint also
available (with full-size figures) from
http://www.astro.ex.ac.uk/people/nfht/publications.html Datacubes available
from http://www.astro.ex.ac.uk/people/nfht/resources.htm
Form Geometry and the 'tHooft-Plebanski Action
Riemannian geometry in four dimensions, including Einstein's equations, can
be described by means of a connection that annihilates a triad of two-forms
(rather than a tetrad of vector fields). Our treatment of the conformal factor
of the metric differs from the original presentation of this result, due to
'tHooft. In the action the conformal factor now appears as a field to be
varied.Comment: 12pp, LaTe
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Performance evaluation of the LumiraDx quantitative microfluidic point-of-care CRP test.
C-reactive protein (CRP) is an established acute-phase marker for infection, inflammation and tissue injury, used to guide clinical decision-making in primary and secondary care. This study compared the analytical performance of the quantitative microfluidic point-of-care LumiraDx CRP Test to a laboratory-based reference method (Siemens RCRP Flex assay on the DimensionŸ XpandŸ) and evaluated equivalence of sample matrices (blood versus plasma) in point-of-care settings using samples from patients presenting with symptoms of infection or inflammation. The LumiraDx CRP Test demonstrated close agreement with the lab reference test (range, 5.1 to 245.2 mg/L, r = 0.992, slope = 0.998, intercept = -0.476; n = 205) and notable agreement between fingerstick and venous blood and plasma (r = 0.974-0.983; n = 44). Paired replicate precision had mean coefficients of variation of 6.4 % (plasma), 6.6 % (capillary direct) and 8.1 % (venous blood); overall error rates were 2.9 %. The quantitative LumiraDx CRP Test showed robust analytical performance across sample matrices and close agreement compared to the laboratory reference method when used at the point of care
Linearized gravity and gauge conditions
In this paper we consider the field equations for linearized gravity and
other integer spin fields on the Kerr spacetime, and more generally on
spacetimes of Petrov type D. We give a derivation, using the GHP formalism, of
decoupled field equations for the linearized Weyl scalars for all spin weights
and identify the gauge source functions occuring in these. For the spin weight
0 Weyl scalar, imposing a generalized harmonic coordinate gauge yields a
generalization of the Regge-Wheeler equation. Specializing to the Schwarzschild
case, we derive the gauge invariant Regge-Wheeler and Zerilli equation directly
from the equation for the spin 0 scalar.Comment: 24 pages, corresponds to published versio
Late-time behaviour of the tilted Bianchi type VI models
We study tilted perfect fluid cosmological models with a constant equation of
state parameter in spatially homogeneous models of Bianchi type VI
using dynamical systems methods and numerical simulations. We study models with
and without vorticity, with an emphasis on their future asymptotic evolution.
We show that for models with vorticity there exists, in a small region of
parameter space, a closed curve acting as the attractor.Comment: 13 pages, 1 figure, v2: typos fixed, minor changes, matches published
versio
Discovery of carbon monoxide in the upper atmosphere of Pluto
Pluto's icy surface has changed colour and its atmosphere has swelled since
its last closest approach to the Sun in 1989. The thin atmosphere is produced
by evaporating ices, and so can also change rapidly, and in particular carbon
monoxide should be present as an active thermostat. Here we report the
discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition,
and find that the line-centre signal is more than twice as bright as a
tentative result obtained by Bockelee-Morvan et al. in 2000. Greater
surface-ice evaporation over the last decade could explain this, or increased
pressure could have caused the atmosphere to expand. The gas must be cold, with
a narrow line-width consistent with temperatures around 50 K, as predicted for
the very high atmosphere, and the line brightness implies that CO molecules
extend up to approximately 3 Pluto radii above the surface. The upper
atmosphere must have changed markedly over only a decade since the prior
search, and more alterations could occur by the arrival of the New Horizons
mission in 2015.Comment: 5 pages; accepted for publication in MNRAS Letter
The Central Engines of 19 LINERs as Viewed by Chandra
Using archival Chandra observations of 19 LINERs we explore the X-ray
properties of their inner kiloparsec to determine the origin of their nuclear
X-ray emission, to investigate the presence of an AGN, and to identify the
power source of the optical emission lines. The relative numbers of LINER types
in our sample are similar to those in optical spectroscopic surveys. We find
that diffuse, thermal emission is very common and is concentrated within the
central few hundred parsec. The average spectra of the hot gas in spirals and
ellipticals are very similar to those of normal galaxies. They can be fitted
with a thermal plasma (kT~0.5 keV) plus a power law (photon index of 1.3-1.5)
model. There are on average 3 detected point sources in their inner kiloparsec
with L(0.5-10 keV)~10^37-10^40 erg/s. The average cumulative luminosity
functions for sources in spirals and ellipticals are identical to those of
normal galaxies. In the innermost circle of 2.5" radius in each galaxy we find
an AGN in 12 of the 19 galaxies. The AGNs contribute a median of 60% of the
0.5-10 keV luminosity of the central 2.5" region, they have luminosities of
10^37-10^39 erg/s (Eddington ratios 10^-8 to 10^-5). The ionizing luminosity of
the AGNs is not enough to power the observed optical emission lines in this
particular sample. Thus, we suggest that the lines are powered either by the
mechanical interaction of an AGN jet (or wind) with the circumnuclear gas, or
by stellar processes, e.g. photoionization by post-AGB stars or young stars.Comment: Accepted by Ap.J. 23 pages, 8 figures, emulatepj format, images of
fig 1 not included, for complete PDF preprint see
http://www.astro.psu.edu/users/mce/preprints
Hard X-ray Luminosities of Multinuclei Infrared Luminous Galaxies Showing a Radio/Far-Infrared Excess
We report the results of hard X-ray observations of four multinuclei merging
infrared luminous galaxies (IRLGs). We selected these four sources for their
excess of radio to far-infrared luminosity ratio compared with starburst
galaxies. This excess suggests that activity associated with a supermassive
black hole (SMBH) contributes strongly to the IRLGs' bolometric luminosities.
Although we expect strong hard X-ray emission from the SMBH-driven activity,
the radio-excess multinuclei merging IRLGs show considerably smaller hard X-ray
luminosities relative to far-infrared (40500 m) and infrared (81000
m) luminosities than active galactic nuclei (AGNs) showing a similar
radio-excess. This result may demonstrate that emission in the hard X-ray
region from SMBH-driven activity in the multinuclei merging IRLGs is severely
suppressed compared to a typical spectral energy distribution of SMBH-driven
activity in AGNs. If this is a common property of merging IRLGs, without its
correction, hard X-ray observations underestimate the contribution of
SMBH-driven activity to the bolometric luminosities of merging IRLGs.Comment: 25 pages of text, 4 figures, aaspp4.sty, Astrophysical Journal, in
press (1999, Volume 527
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