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 $\tau_{max} = (1.0 \pm 0.08) \times 10^{-2}$, $(1.4 \pm 0.2) \times 10^{-3}$, $(2.2 \pm 0.5) \times 10^{-3}$ and $(3.4 \pm 0.5) \times 10^{-3}$ and kinetic temperatures $T_{k} = 3127 \pm 300$ K, $3694 \pm 1595$ K, $3500 \pm 1354$ K and $2165 \pm 608$ K respectively. All four components were thus found to have temperatures in the thermally unstable range $500 < T_{k} < 5000$ 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 $\sim (0.3-2)\times 10^{8} yr$ 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