181 research outputs found
MRC B0319-454: Probing the large-scale structure with a giant radio galaxy
We present an investigation of the relationships between the radio properties
of a giant radio galaxy MRC B0319-454 and the surrounding galaxy distribution
with the aim of examining the influence of intergalactic gas and gravity
associated with the large-scale structure on the evolution in the radio
morphology. Our new radio continuum observations of the radio source, with high
surface brightness sensitivity, images the asymmetries in the megaparsec-scale
radio structure in total intensity and polarization. We compare these with the
3-D galaxy distribution derived from galaxy redshift surveys. Galaxy density
gradients are observed along and perpendicular to the radio axis: the
large-scale structure is consistent with a model wherein the galaxies trace the
ambient intergalactic gas and the evolution of the radio structures are
ram-pressure limited by this associated gas. Additionally, we have modeled the
off-axis evolution of the south-west radio lobe as deflection of a buoyant jet
backflow by a transverse gravitational field: the model is plausible if
entrainment is small. The case study presented here is a demonstration that
giant radio galaxies may be useful probes of the warm-hot intergalactic medium
believed to be associated with moderately over dense galaxy distributions.Comment: 27 pages, 15 figures, accepted for publication in MNRA
The temperature of the WNM in the Milky Way
We report high spectral resolution Australia Telescope Compact Array HI 21 cm
observations resulting in the detection of the warm neutral medium (WNM) of the
Galaxy in absorption against two extragalactic radio sources, PKS 1814-637 and
PKS 0407-658. The two lines of sight were selected on the basis of the
simplicity of their absorption profiles and the strength of the background
sources; the high velocity resolution of the spectra then enabled us to
estimate the kinetic temperatures of the absorbing gas by fitting multiple
Gaussians to the absorption profiles. Four separate WNM components were
detected toward the two sources, with peak optical depths , , and and kinetic temperatures
K, K, K and K respectively. All four components were thus found to have temperatures
in the thermally unstable range K; this suggests that
thermal equilibrium has not been reached throughout the WNM.Comment: 5 pages, 6 figures. Accepted for publication in MNRAS (Letters).
Minor typos removed to match version in pres
A study of the environments of large radio galaxies using SDSS
The distributions of galaxies in the environments of 16 large radio sources
have been examined using the Sloan Digital Sky Survey. In the giant radio
galaxy J1552+2005 (3C326) which has the highest arm-length ratio, the shorter
arm is found to interact with a group of galaxies which forms part of a
filamentary structure. Although most large sources occur in regions of low
galaxy density, the shorter arm is brighter in most cases suggesting
asymmetries in the intergalactic medium which may not be apparent in the
distribution of galaxies. In two cases with strong and variable cores,
J0313+4120 and J1147+3501, the large flux density asymmetries are possibly also
caused by the effects of relativistic motion.Comment: Accepted for publication in MNRA
PKS B1545-321: Bow shocks of a relativistic jet?
Sensitive, high resolution images of the double-double radio galaxy PKS
B1545-321 reveal detailed structure, which we interpret in the light of
previous work on the interaction of restarted jets with pre-existing relict
cocoons. We have also examined the spectral and polarization properties of the
source, the color distribution in the optical host and the environment of this
galaxy in order to understand its physical evolution. We propose that the
restarted jets generate narrow bow shocks and that the inner lobes are a
mixture of cocoon plasma reaccelerated at the bow shock and new jet material
reaccelerated at the termination shock. The dynamics of the restarted jets
implies that their hot spots advance at mildly relativistic speeds with
external Mach numbers of at least 5. The existence of supersonic hot spot Mach
numbers and bright inner lobes is the result of entrainment causing a reduction
in the sound speed of the pre-existing cocoon. The interruption to jet activity
in PKS B1545-321 has been brief - lasting less than a few percent of the
lifetime of the giant radio source. The host
galaxy is located at the boundary of a large scale filamentary structure, and
shows blue patches in color distribution indicative of a recent merger, which
may have triggered the Mpc-scale radio galaxy.Comment: 26 pages including 1 table and 16 figures. To appear in MNRA
Double-double radio galaxies: further insights into the formation of the radio structures
Double-double radio galaxies (DDRGs) offer a unique opportunity for us to
study multiple episodes of jet activity in large-scale radio sources. We use
radio data from the Very Large Array and the literature to model two DDRGs,
B1450+333 and B1834+620, in terms of their dynamical evolution. We find that
the standard Fanaroff-Riley II model is able to explain the properties of the
two outer lobes of each source, whereby the lobes are formed by ram-pressure
balance of a shock at the end of the jet with the surrounding medium. The inner
pairs of lobes, however, are not well-described by the standard model. Instead
we interpret the inner lobes as arising from the emission of relativistic
electrons within the outer lobes, which are compressed and re-accelerated by
the bow-shock in front of the restarted jets and within the outer lobes. The
predicted rapid progression of the inner lobes through the outer lobes requires
the eventual development of a hotspot at the edge of the outer lobe, causing
the DDRG ultimately to resemble a standard Fanaroff-Riley II radio galaxy. This
may suggest that DDRGs are a brief, yet normal, phase of the evolution of
large-scale radio galaxies.Comment: Accepted for publication in MNRAS. 17 pages; 15 figures, 2 of which
are in colou
A dynamical model for FR II type radio sources with terminated jet activity
The extension of the KDA analytical model of FR II-type source evolution
originally assuming a continuum injection process in the jet-IGM (intergalactic
medium) interaction towards a case of the jet's termination is presented and
briefly discussed. The dynamical evolution of FR II-type sources predicted with
this extended model, hereafter referred to as KDA EXT, and its application to
the chosen radio sources. Following the classical approach based on the
source's continuous injection and self-similarity, I propose the effective
formulae describing the length and luminosity evolution of the lobes during an
absence of the jet flow, and present the resulting diagrams for the
characteristics mentioned. Using an algorithm based on the numerical
integration of a modified formula for jet power, the KDA EXT model is fitted to
three radio galaxies. Their predicted spectra are then compared to the observed
spectra, proving that these fits are better than the best spectral fit provided
by the original KDA model of the FR II-type sources dynamical evolution
Rejuvenated radio galaxies J0041+3224 and J1835+6204 : how long can the quiescent phase of nuclear activity last?
We present radio observations of two well-known doubledouble radio galaxies, J0041+3224 and J1835+6204, at frequencies ranging from 150 to 8460 MHz, using both the Giant Metrewave Radio Telescope and the Very Large Array. These observations, over a large radio frequency range, enable us to determine the spectra of the inner and outer lobes. Our detailed spectral ageing analysis of their inner and outer lobes demonstrates that the outer doubles of doubledouble radio galaxies are created by the previous cycle of activity, while the inner doubles are due to the present cycle of activity. The (core subtracted) spectra of the inner doubles of both sources are power laws over a large frequency range. We found that the duration of the quiescent phase of J0041+3224 is between 4 and 28 per cent of the active phase of the previous activity. The outer north-western lobe of J1835+6204 has a compact hotspot and the regions of both the outer hotspots have close to power-law (rather than curved) spectra, which indicates that the outer lobes are still fed by jet material ejected in the previous episode just before the central engine stopped powering the jet. We estimate that the duration of the quiescent phase of J1835+6204 is ?5 per cent of the duration of the active phase of the previous activity. Therefore, we conclude that the duration of the quiescent phase can be as short as a few per cent of the active phase in radio galaxies of this type.Peer reviewe
Endovascular Treatment for Acute Basilar Artery Occlusion: A Fragility Index Meta-Analysis
Introduction: High-quality evidence regarding the use of endovascular treatment (EVT) in patients with acute basilar artery occlusion (BAO) has been provided by recently completed randomized controlled clinical trials (RCTs). Methods: We conducted a systematic review and meta-analysis including all available RCTs that investigated efficacy and safety of EVT in addition to best medical treatment (BMT) versus BMT alone for BAO. The random-effects model was used, while the fragility index (FI) was calculated for dichotomous outcomes of interest. Results: Four RCTs were included comprising a total of 988 patients with acute BAO (mean age: 65.6 years, 70% men, median NIHSS: 24, 39% pretreatment with intravenous thrombolysis). EVT was related to higher likelihood of good functional outcome (RR: 1.54; 95% CI: 1.16–2.05; I2 = 60%), functional independence (RR: 1.83; 95% CI: 1.08–3.08; I2 = 79%) and reduced disability at 3 months (adjusted common OR: 1.96; 95% CI: 1.26–3.05; I2 = 59%) compared to BMT alone. Despite that EVT was associated with a higher risk for symptomatic intracranial hemorrhage (RR: 7.78; 95% CI: 2.36–25.61; I2 = 0%) and any intracranial hemorrhage (RR: 2.85; 95% CI: 1.50–5.44; I2 = 16%), mortality at 3 months was lower among patients that received EVT plus BMT versus BMT alone (RR: 0.76; 95% CI: 0.65–0.89; I2 = 0%). However, sufficient robustness was not evident in any of the reported associations (FI < 10) including the overall effect regarding the primary outcome. The former associations were predominantly driven by RCTs with recruitment limited in China. Conclusions: EVT combined with BMT is associated with a higher likelihood of achieving good functional outcomes and a lower risk of death at 3 months compared to BMT alone, despite the higher risk of sICH. An individual-patient data meta-analysis is warranted to uncover and adjust for potential sources of heterogeneity and to provide further insight
The extraordinary radio galaxy MRC B1221-423: probing deeper at radio and optical wavelengths
We present optical spectra and high-resolution multi-wavelength radio
observations of the compact steep-spectrum radio source MRC B1221-423
(z=0.1706). MRC B1221-423 is a very young (~10^5 yr), powerful radio source
which is undergoing a tidal interaction with a companion galaxy. We find strong
evidence of interaction between the AGN and its environment. The radio
morphology is highly distorted, showing a dramatic interaction between the
radio jet and the host galaxy, with the jet being turned almost back on itself.
H I observations show strong absorption against the nucleus at an infall
velocity of ~250 km/s compared to the stellar velocity, as well as a second,
broader component which may represent gas falling into the nucleus. Optical
spectra show that star formation is taking place across the whole system. Broad
optical emission lines in the nucleus show evidence of outflow. Our
observations confirm that MRC B1221-423 is a young radio source in a gas-rich
nuclear environment, and that there was a time delay of a few x 100 Myr between
the onset of star formation and the triggering of the AGN.Comment: 15 pages, 13 figures, to appear in MNRA
Intravenous thrombolysis for acute ischemic stroke in Greece: the Safe Implementation of Thrombolysis in Stroke registry 15-year experience
Background: Intravenous thrombolysis (IVT) remains the only approved systemic reperfusion treatment for acute ischemic stroke (AIS), however there are scarce data regarding outcomes and complications of IVT in Greece. We evaluated safety and efficacy outcomes of IVT for AIS in Greece using the Safe Implementation of Thrombolysis in Stroke: International Stroke Thrombolysis Register (SITS-ISTR) dataset.
Methods: All AIS patients treated with IVT in Greece between December 2002 and July 2017 and recorded in the SITS-ISTR were evaluated. Demographics, risk factors, baseline stroke severity [defined using National Institutes of Health Stroke Scale (NIHSS)], and onset-to-treatment time (OTT) were recorded. Safety outcomes included symptomatic intracranial hemorrhage (sICH) and 3-month mortality rates. The efficacy outcomes evaluated a reduction in baseline NIHSS score at 2 and 24 h following IVT onset, 3-month favorable functional outcome [FFO; modified Rankin scale (mRS) scores of 0-1] and 3-month functional independence (FI; mRS-scores of 0-2). The safety and efficacy outcomes were assessed comparatively with previously published data from SITS national and international registries.
Results: A total of 523 AIS patients were treated with IVT in 12 Greek centers participating in the SITS-ISTR during the study period (mean age 62.4 ± 12.7; 34.6% women; median baseline NIHSS score: 11 points; median OTT: 150 min). The rates of sICH were 1.4%, 2.3%, and 3.8% according to the SIST-MOST, ECASS II, and NINDS criteria respectively. The median reduction in NIHSS score at 2 and 24 h was 3 [interquartile range (IQR): 1-5] and 5 (IQR: 2-8) points respectively. The 3-month FI, FFO and mortality were 66.5%, 55.6% and 7.9%. All safety and efficacy outcomes were comparable with available data from SITS-ISTR in other European countries.
Conclusions: Our study underscores the safety and efficacy of IVT for AIS in Greece. Additional action is necessary in order to increase the availability of IVT in the Greek population and to include more centers in the SITS-ISTR
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