9,185 research outputs found
Deep radio observations of 3C324 and 3C368: evidence for jet-cloud interactions
High resolution, deep radio images are presented for two distant radio
galaxies, 3C324 (z=1.206) and 3C368 (z=1.132), which are both prime examples of
the radio-optical alignment effect seen in powerful radio galaxies with
redshifts z > 0.6. Radio observations were made using the Very Large Array in
A-array configuration at 5 and 8 GHz, and using the MERLIN array at 1.4 and
1.65 GHz. Radio spectral index, radio polarisation, and rotation measure maps
are presented for both sources. Radio core candidates are detected in each
source, and by aligning these with the centroid of the infrared emission the
radio and the optical/infrared images can be related astrometrically with 0.1
arcsec accuracy. In each source the radio core is located at a minimum of the
optical emission, probably associated with a central dust lane. Both sources
also exhibit radio jets which lie along the directions of the bright strings of
optical knots seen in high resolution Hubble Space Telescope images. The
northern arm of 3C368 shows a close correlation between the radio and optical
emission, whilst along the jet direction of 3C324 the bright radio and optical
knots are co-linear but not co-spatial. These indicate that interactions
between the radio jet and its environment play a key role in producing the
excess ultraviolet emission of these sources, but that the detailed mechanisms
vary from source to source. 3C368 is strongly depolarised and has an average
rest-frame rotation measure of a few hundred rad/m^2, reaching about 1000
rad/m^2 close to the most depolarised regions. 3C324 has weaker depolarisation,
and an average rest-frame rotation measure of between 100 and 200 rad/m^2. Both
sources show large gradients in their rotation measure structures, with
variations of up to 1000 rad/m^2 over distances of about 10 kpc.Comment: 15 pages including 4 figures. LaTeX. Accepted for publication in
MNRA
Defying jet-gas alignment in two radio galaxies at z~2 with extended light profiles: Similarities to brightest cluster galaxies
We report the detection of extended warm ionized gas in two powerful
high-redshift radio galaxies, NVSS J210626-314003 at z=2.10 and TXS 2353-003 at
z=1.49, that does not appear to be associated with the radio jets. This is
contrary to what would be expected from the alignment effect, a characteristic
feature of distant, powerful radio galaxies at z> 0.6. The gas also has smaller
velocity gradients and line widths than most other high-z radio galaxies with
similar data. Both galaxies are part of a systematic study of 50 high-redshift
radio galaxies with SINFONI, and are the only two that are characterized by the
presence of high surface-brightness gas not associated with the jet axis and by
the absence of such gas aligned with the jet. Both galaxies are spatially
resolved with ISAAC broadband imaging covering the rest-frame R band, and have
extended wings that cannot be attributed to line contamination. We argue that
the gas and stellar properties of these galaxies are more akin to gas-rich
brightest cluster galaxies in cool-core clusters than the general population of
high-redshift radio galaxies at z>2. In support of this interpretation, one of
our sources, TXS 2353-003, for which we have H\alpha\ narrowband imaging, is
associated with an overdensity of candidate H\alpha\ emitters by a factor of 8
relative to the field at z=1.5. We discuss possible scenarios of the
evolutionary state of these galaxies and the nature of their emission line gas
within the context of cyclical AGN feedback.Comment: A&A in pres
Relativistic Kinetic Equations for Electromagnetic, Scalar and Pseudoscalar Interactions
We derive the kinetic equations for both the covariant and equal-time Wigner
functions of Dirac particles with electromagnetic, scalar and pseudoscalar
interactions. We emphasize the constraint equations for the spinor components
in the equal-time formulation.Comment: 12 pages, no figures, revte
VLT spectropolarimetry of two powerful radio galaxies at z~1.4: UV continuum, emission-line properties and the nature of high-redshift dust
(Abridged) Deep VLT spectropolarimetric observations are presented for two
powerful radio galaxies, 0850-206 and 1303+091. These observations cover the
rest-frame wavelength range ~ 1450 - 3750 A. New radio observations and
continuum images of the same sources are also presented. These galaxies are the
first two observed from a complete sample of nine radio sources with redshifts
in the range 1.3 < z < 1.5 (selected from the equatorial sample of powerful
radio sources of Best, Rottgering & Lehnert), as part of a project aimed to
investigate the multi-component nature of the UV continuum in radio galaxies
and any variations of the continuum properties with the radio source age.
The larger radio source of the two, 0850-206, presents a high continuum
fractional polarization, averaging 17% across the observed wavelength range and
reaching 24% at rest-frame wavelengths of <2000 A. The smaller radio source,
1303+091, shows a lower continuum polarization, averaging 8% and rising to 11%
for rest-frame wavelengths >3000 A. For both galaxies, the position angle of
the electric vector is generally constant with wavelength and within ~15
degrees of perpendicular to the radio axis. Both their total flux spectra and
polarized flux spectra reveal the 2200 A dust feature, and comparison with dust
scattering models suggests that the composition of the dust in these galaxies
is similar to that of Galactic dust. In 0850-206, scattered quasar radiation
dominates the UV continuum emission, with the nebular continuum accounting for
no more than ~22% and no requirement for any additional emission component such
as emission from young stars. By contrast, in 1303+091, unpolarized radiation
could be a major constituent of the UV continuum emission, with starlight
accounting for up to ~50% and the nebular continuum accounting for ~11%.Comment: 20 pages, including 14 figures. MNRAS accepte
The Prolongation of Insulin Action
Author Institution: Department of Physiology, University of Toront
Homeostatic mechanisms in dopamine synthesis and release: a mathematical model
<p>Abstract</p> <p>Background</p> <p>Dopamine is a catecholamine that is used as a neurotransmitter both in the periphery and in the central nervous system. Dysfunction in various dopaminergic systems is known to be associated with various disorders, including schizophrenia, Parkinson's disease, and Tourette's syndrome. Furthermore, microdialysis studies have shown that addictive drugs increase extracellular dopamine and brain imaging has shown a correlation between euphoria and psycho-stimulant-induced increases in extracellular dopamine <abbrgrp><abbr bid="B1">1</abbr></abbrgrp>. These consequences of dopamine dysfunction indicate the importance of maintaining dopamine functionality through homeostatic mechanisms that have been attributed to the delicate balance between synthesis, storage, release, metabolism, and reuptake.</p> <p>Methods</p> <p>We construct a mathematical model of dopamine synthesis, release, and reuptake and use it to study homeostasis in single dopaminergic neuron terminals. We investigate the substrate inhibition of tyrosine hydroxylase by tyrosine, the consequences of the rapid uptake of extracellular dopamine by the dopamine transporters, and the effects of the autoreceoptors on dopaminergic function. The main focus is to understand the regulation and control of synthesis and release and to explicate and interpret experimental findings.</p> <p>Results</p> <p>We show that the substrate inhibition of tyrosine hydroxylase by tyrosine stabilizes cytosolic and vesicular dopamine against changes in tyrosine availability due to meals. We find that the autoreceptors dampen the fluctuations in extracellular dopamine caused by changes in tyrosine hydroxylase expression and changes in the rate of firing. We show that short bursts of action potentials create significant dopamine signals against the background of tonic firing. We explain the observed time courses of extracellular dopamine responses to stimulation in wild type mice and mice that have genetically altered dopamine transporter densities and the observed half-lives of extracellular dopamine under various treatment protocols.</p> <p>Conclusion</p> <p>Dopaminergic systems must respond robustly to important biological signals such as bursts, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of tyrosine hydroxylase, the dopamine transporters, and the dopamine autoreceptors.</p
Measurement of 25Mg(p; gamma)26Al resonance strengths via gamma spectrometry
The COMPTEL instrument performed the first mapping of the 1.809 MeV photons
in the Galaxy, triggering considerable interest in determing the sources of
interstellar 26Al. The predicted 26Al is too low compared to the observation,
for a better understanding more accurate rates for the 25Mg(p; gamma)26Al
reaction are required. The 25Mg(p;gamma)26Al reaction has been investigated at
the resonances at Er= 745; 418; 374; 304 keV at Ruhr-Universitat-Bochum using a
Tandem accelerator and a 4piNaI detector. In addition the resonance at Er = 189
keV has been measured deep underground laboratory at Laboratori Nazionali del
Gran Sasso, exploiting the strong suppression of cosmic background. This low
resonance has been studied with the 400 kV LUNA accelerator and a HPGe
detector. The preliminary results of the resonance strengths will be reported.Comment: Accepted for publication in Journal of Physics
Double Lobed Radio Quasars from the Sloan Digital Sky Survey
We have combined a sample of 44984 quasars, selected from the Sloan Digital
Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel
technique where the optical quasar position is matched to the complete radio
environment within 450", we are able to characterize the radio morphological
make-up of what is essentially an optically selected quasar sample, regardless
of whether the quasar (nucleus) itself has been detected in the radio. About
10% of the quasar population have radio cores brighter than 0.75 mJy at 1.4
GHz, and 1.7% have double lobed FR2-like radio morphologies. About 75% of the
FR2 sources have a radio core (> 0.75 mJy). A significant fraction (~40%) of
the FR2 quasars are bent by more than 10 degrees, indicating either
interactions of the radio plasma with the ICM or IGM. We found no evidence for
correlations with redshift among our FR2 quasars: radio lobe flux densities and
radio source diameters of the quasars have similar distributions at low (mean
0.77) and high (mean 2.09) redshifts. Using a smaller high reliability FR2
sample of 422 quasars and two comparison samples of radio-quiet and non-FR2
radio-loud quasars, matched in their redshift distributions, we constructed
composite optical spectra from the SDSS spectroscopic data. Based on these
spectra we can conclude that the FR2 quasars have stronger high-ionization
emission lines compared to both the radio quiet and non-FR2 radio loud sources.
This is consistent with the notion that the emission lines are brightened by
ongoing shock ionization of ambient gas in the quasar host as the radio source
expands.Comment: 20 pages, 10 figures - some of which have been reduced in quality /
size. Accepted for publication in the Astronomical Journa
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