Bubbles in Planetary Nebulae and Clusters of Galaxies: Instabilities at Bubble Fronts

I study the stability of off-center low-density more or less spherical (fat) bubbles in clusters of galaxies and in planetary nebulae (PNs) to Rayleigh-Taylor (RT) instability. As the bubble expands and decelerates, the interface between the low-density bubble's interior and the dense shell formed from the accreted ambient medium is RT-stable. If, however, in a specific direction the density decreases such that this segment is accelerated by the pressure inside the bubble, then this accelerated region is RT-unstable. The outermost region, relative to the center of the system, is the most likely to become unstable because there the density gradient is the steepest. Using simple analytical analysis, I find that off-center fat bubbles in PNs are much less stable than in clusters. In PNs bubbles become unstable when they are very small relative to their distance from the center; they can be stabilized somewhat if the mass loss rate from the stellar progenitor decreases for a time, such that the negative density gradient is much shallower. In clusters fat bubbles become unstable when their size is comparable to their distance from the center. I discuss some implications of this instability in clusters and in PNs.Comment: New Astronomy, in press; a third in a series of 3 paper

Evidence of unrelaxed IGM around IC1262

AIMS: A peculiar morphology of the hot gas was discovered at the center of IC1262 with the ROSAT HRI. Sensitive Chandra and XMM-Newton data were requested to investigate the characteristics of this structure to understand its nature. METHODS: We have exploited the high resolution and sensitivity of Chandra's ACIS-S to investigate the peculiar morphology and spectral characteristics of hot gas in the group around IC1262. XMM-Newton data are only partially usable due to very heavy high background contamination, but they are useful to confirm and strengthen the results from Chandra. RESULTS: The Chandra data show a quite dramatic view of the \object{IC1262} system: a sharp discontinuity east of the central galaxy, with steep drops and a relatively narrow feature over 100 kpc long, plus an arc/loop to the N, are all indicative of a turmoil in the high energy component. Their morphologies could suggest them to be tracers of shocked material caused either by peculiar motions in the system or by a recent merger process, but the spectral characteristics indicate that the structure is cooler than its surroundings. The lack of evidence of significant structures in the velocity distribution of the group members and the estimated scale of the phenomenon make the interpretation of its physical nature challenging. We review a few possible interpretations, in light of similar phenomena observed in clusters and groups. The ram pressure stripping of a bright spiral galaxy, now near the center of the group, is a promising interpretation for most of the features observed. The relation with the radio activity requires a better sampling of the radio parameters that can only be achieved with deeper and higher resolution observations.Comment: Accepted for pubblication in Astronomy & Astrophysics. Figs 1, 2, 3 and 9-12 are given as JPEG files due to the restrictions on space available on astro-p

Explaining the Energetic AGN Outburst of MS0735+7421 with Massive Slow Jets

By conducting axisymmetrical hydrodynamical numerical simulations (2.5 dimensional code) we show that slow, massive, wide jets can reproduce the morphology of the huge X-ray deficient bubble pair in the cluster of galaxies MS0735+7421. The total energy of the jets, composed of the energy in the bubble pair and in the shock wave, is constraint by observations conducted by McNamara et al. (2009) to be ~10^{62}erg. We show that two opposite jets that are active for ~100Myr, each with a launching half opening angle of ~70 degrees, an initial velocity of ~0.1c, and a total mass loss rate of the two jets of ~100 Mo/year, can account for the observed morphology. Rapidly precessing narrow jets can be used instead of wide jets. In our model the cluster suffered from a cooling catastrophe ~100Myr ago. Most of the mass that cooled, ~10^{10} Mo, was expelled back to the intracluster medium (ICM) by the AGN activity and is inside the bubbles now, ~10% formed stars, and ~10% of the cold gas was accreted by the central black hole and was the source of the outburst energy. This type of activity is similar to that expected to occur in galaxy formation.Comment: Accepted by MNRA

Binary Black Holes at the Core of Galaxy Clusters

In this paper we push forward and exploit an analogy between the morphologies of the X-ray cavities observed in some galaxy clusters, and the optically deficient point-symmetric bubbles occurring in some planetary nebulae (PNe). Point-symmetric PNe are thought to be shaped by stellar binary interactions; namely, the presence of a companion to the PN's progenitor star is required. We suggest that similar point-symmetric structures in the X-ray cavities of galaxy clusters might be associated with the presence of massive binary black holes. A systematic cataloguing of high-resolution images of the diffuse X-ray emission at the core of galaxy clusters might contribute to individuate massive binary black holes.Comment: Accepted for publication in "Advances in Space Research" (Proceedings of the 35th COSPAR Assembly 2004; Session "New Insights from XMM-Newton, Chandra and INTEGRAL"

Risks and benefits of optimised medical and revascularisation therapy in elderly patients with angina - on-treatment analysis of the TIME trial

Aim To assess treatment effects of optimised medical therapy and PCI or CABG surgery on one-year outcome in patients ⩾75 years old with chronic angina. Methods and Results On-treatment analysis of the TIME data: all re-vascularised patients (REVASC \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $n=174$ \end{document}: 112 randomised to revascularisation and 62 to drugs with late revascularisation) were compared to all patients on continued drug therapy (MED \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $n=127$ \end{document}: 86 randomised to drugs and 41 to revascularisation only). Baseline characteristics of both groups were similar (age 80±4 years). Risk of death at one year (adjusted hazard ratio (HR)=1.31; 95%-CI: 0.58-2.99; \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $P=0.52$ \end{document}) and of death/infarction (adjusted hazard ratio=1.77; 95%-CI 0.91-3.41; \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $P=0.09$ \end{document}) were comparable between REVASC and MED patients. Furthermore, the risk of death within 30 days was even slightly lower among REVASC patients (unadjusted hazard ratio=0.73; 95%-CI: 0.21-2.53; \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $P=0.98)$ \end{document}. Overall, REVASC patients had greater improvements in symptoms and well-being than MED patients \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $(P{<}0.01)$ \end{document}. Surgical patients had similar mortality rates as angioplasty patients, but they also had greater symptomatic improvements \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} $(P{<}0.01)$ \end{document}. Conclusion Treated medically, elderly patients with chronic angina have a similarly high 30-day and one-year mortality as patients of the same age being re-vascularised; however, they can expect lower improvements in symptoms and well bein

The local structure of molecular reaction intermediates at surfaces

A critical review is presented of the results of (experimental) quantitative structural studies of molecular reaction intermediates at surfaces; i.e. molecular species that do not exist naturally in the gas phase and, in most cases, are implicated in surface catalytic processes. A brief review of the main experimental methods that have contributed to this area is followed by a summary of the main results. Investigated species include: carboxylates, RCOO– (particularly formate, but also deprotonated amino acids); methoxy, CH3O–; carbonate, CO3; ethylidyne, CH3C–; NHx and SOx species; cyanide, CN. As far as possible in the limited range of systems studied, a few general trends are identified

Metal enrichment processes

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Interaction of Fanaroff-Riley class II radio jets with a randomly magnetised intra-cluster medium

A combination of three-dimensional (3D) magnetohydrodynamics (MHD) and synthetic numerical simulations are presented to follow the evolution of a randomly magnetised plasma that models the intra-cluster medium (ICM), under the isolated effects of powerful, light, hypersonic and bipolar Fanaroff-Riley class II (FR II) jets. We prescribe the cluster magnetic field (CMF) as a Gaussian random field with a Kolmogorov-like energy spectrum. Both the power of the jets and the viewing angle that is used for the synthetic Rotation Measure (RM) observations are investigated. We find the model radio sources introduce and amplify fluctuations on the RM statistical properties which we analyse as a function of time as well as the viewing angle. The average RM and the RM standard deviation are increased by the action of the jets. Energetics, RM statistics and magnetic power spectral analysis consistently show that the effects also correlate with the jets' power, and that the lightest, fastest jets produce the strongest changes in their environment. We see jets distort and amplify the CMFs especially near the edges of the lobes and the jets' heads. This process leads to a flattening of the RM structure functions at scales comparable to the source size. The edge features we find are similar to ones observed in Hydra A. The results show that jet-produced RM enhancements are more apparent in quasars than in radio galaxies. Globally, jets tend to enhance the RM standard deviation which may lead to overestimations of the CMFs' strength by about 70%. This study means to serve as a pathfinder for the SKA, EVLA and LOFAR to follow the evolution of cosmic magnetic fields.Comment: Accepted for publication in the MNRAS. 21 pages, 15 figure

Metallicity map of the galaxy cluster A3667

We use XMM-Newton data of the merging cluster Abell 3667 to analyze its metallicity distribution. A detailed abundance map of the central 1.1x1.1 Mpc region indicates that metals are inhomogeneously distributed in the cluster showing a non-uniform and very complex metal pattern. The highest peak in the map corresponds to a cold region, slightly offset South of the X-ray center. This could be interpreted as stripped gas due to a merger between a group moving from NW towards the SE and the main cluster. We note several clumps of high metallicity also in the opposite direction with respect to the X-ray peak. Furthermore we determined abundances for 5 elements (O, Si, S, Ar, Fe) in four different regions of the cluster. Comparisons between these observed abundances and theoretical supernovae yields allow to get constraints on the relative number of SN Ia and II contributing to the enrichment of the intra-cluster medium. To reproduce the observed abundances of the best determined elements (Fe, O and Si) in a region of 7 arcmin around the X-ray center, 65-80% of SN II are needed. The comparison between the metal map, a galaxy density map obtained using 550 spectroscopically confirmed cluster members and our simulations suggest a recent merger between the main cluster and the group in the SE.Comment: 10 pages, 10 figure