Constraining the Nature of X-ray Cavities in Clusters and Galaxies

We present results from an extensive survey of 64 cavities in the X-ray halos of clusters, groups and normal elliptical galaxies. We show that the evolution of the size of the cavities as they rise in the X-ray atmosphere is inconsistent with the standard model of adiabatic expansion of purely hydrodynamic models. We also note that the majority of the observed bubbles should have already been shredded apart by Rayleigh-Taylor and Richtmyer-Meshkov instabilities if they were of purely hydrodynamic nature. Instead we find that the data agrees much better with a model where the cavities are magnetically dominated and inflated by a current-dominated magneto-hydrodynamic jet model, recently developed by Li et al. (2006) and Nakamura et al. (2006). We conduct complex Monte-Carlo simulations of the cavity detection process including incompleteness effects to reproduce the cavity sample's characteristics. We find that the current-dominated model agrees within 1sigma, whereas the other models can be excluded at >5sigma confidence. To bring hydrodynamic models into better agreement, cavities would have to be continuously inflated. However, these assessments are dependent on our correct understanding of the detectability of cavities in X-ray atmospheres, and will await confirmation when automated cavity detection tools become available in the future. Our results have considerable impact on the energy budget associated with active galactic nucleus feedback.Comment: 21 pages, 12 figures, emulateapj, accepted for publication in ApJ, responded to referee's comments and added a new model, conclusions unchange

The Pyrite and Marcasite Electrodes

Pyrite and marcasite may be used as the indicating electrode in neutralization reactions. In acid solution the pyrite and marcasite electrodes behave almost identically with the platinum electrode with differences arising (1) in the presence of strong oxidizing agents where the attack on the pyrite and marcasite alters the potential, and (2) long standing where changes result from the dissolution of a little pyrite even under non-oxidizing conditions. Pyrite and marcasite can thus be used as indicator electrodes in oxidation-reduction titrations. A pyrite-platinum pair gives a differential titration curve. In alkaline solution pyrite, marcasite and platinum respond almost identically to changes in the concentration of sulfide, the single electrode potentials being shifted 120 mv. negative for each ten-fold increase in sulfide concentration

Interacting crumpled manifolds

In this article we study the effect of a delta-interaction on a polymerized membrane of arbitrary internal dimension D. Depending on the dimensionality of membrane and embedding space, different physical scenarios are observed. We emphasize on the difference of polymers from membranes. For the latter, non-trivial contributions appear at the 2-loop level. We also exploit a ``massive scheme'' inspired by calculations in fixed dimensions for scalar field theories. Despite the fact that these calculations are only amenable numerically, we found that in the limit of D to 2 each diagram can be evaluated analytically. This property extends in fact to any order in perturbation theory, allowing for a summation of all orders. This is a novel and quite surprising result. Finally, an attempt to go beyond D=2 is presented. Applications to the case of self-avoiding membranes are mentioned

Clues on black hole feedback from simulated and observed X-ray properties of elliptical galaxies

The centers of elliptical galaxies host supermassive black holes that significantly affect the surrounding interstellar medium through feedback resulting from the accretion process. The evolution of this gas and of the nuclear emission during the galaxies' lifetime has been studied recently with high-resolution hydrodynamical simulations. These included gas cooling and heating specific for an average AGN spectral energy distribution, a radiative efficiency declining at low mass accretion rates, and mechanical coupling between the hot gas and AGN winds. Here we present a short summary of the observational properties resulting from the simulations, focussing on 1) the nuclear luminosity; 2) the global luminosity and temperature of the hot gas; 3) its temperature profile and X-ray brightness profile. These properties are compared with those of galaxies of the local universe, pointing out the successes of the adopted feedback and the needs for new input in the simulations.Comment: 15 pages, 6 figures, accepted for publication in Advances in Space Researc

Spatial Distribution of Nucleosynthesis Products in Cassiopeia A: Comparison Between Observations and 3D Explosion Models

We examine observed heavy element abundances in the Cassiopeia A supernova remnant as a constraint on the nature of the Cas A supernova. We compare bulk abundances from 1D and 3D explosion models and spatial distribution of elements in 3D models with those derived from X-ray observations. We also examine the cospatial production of 26Al with other species. We find that the most reliable indicator of the presence of 26Al in unmixed ejecta is a very low S/Si ratio (~0.05). Production of N in O/S/Si-rich regions is also indicative. The biologically important element P is produced at its highest abundance in the same regions. Proxies should be detectable in supernova ejecta with high spatial resolution multiwavelength observations.Comment: To appear in the Conference Proceedings for the "10th Symposium on Nuclei in the Cosmos (NIC X)", July 27 - August 1 2008, Mackinack Island, Michigan, US

Systematic study of X-ray Cavities in the brightest galaxy of the Draco Constellation NGC 6338

We present results based on the systematic analysis of currently available Chandra archive data on the brightest galaxy in the Draco constellation NGC 6338, in order to investigate the properties of the X-ray cavities. In the central ~6 kpc, at least a two and possibly three, X-ray cavities are evident. All these cavities are roughly of ellipsoidal shapes and show a decrement in the surface brightness of several tens of percent. In addition to these cavities, a set of X-ray bright filaments are also noticed which are spatially coincident with the H{\alpha} filaments over an extent of 15 kpc. The H{\alpha} emission line filaments are perpendicular to the X- ray cavities. Spectroscopic analysis of the hot gas in the filaments and cavities reveal that the X-ray filaments are cooler than the gas contained in the cavities. The emission line ratios and the extended, asymmetric nature of the H{\alpha} emission line filaments seen in this system require a harder ionizing source than that produced by star formation and/or young, massive stars. Radio emission maps derived from the analysis of 1.4 GHz VLA FIRST survey data failed to show any association of these X-ray cavities with radio jets, however, the cavities are filled by radio emission. The total power of the cavities is 17\times 1042 erg s-1 and the ratio of the radio luminosity to cavity power is ~ 10-4, implying that most of the jet power is mechanical.Comment: The paper contains 12 figures and 3 tables, Accepted 2011 December 7 for publication in MNRA

From Resistance to Receptiveness: Farmer Willingness to Participate in Extension Discussions About Climate Variability and Climate Change

Identifying what Extension professionals believe are the critical elements of a communication strategy that is most likely to encourage agricultural producers to participate in discussions of climate variability and climate change is pivotal to providing timely solutions to issues facing farmers. The current study involved interviews with 50 Extension professionals from four southeastern states (Alabama, Florida, Georgia, and South Carolina) who were engaged in ongoing work related to climate and agriculture. Respondents were asked to assess how best to engage farmers in conversations related to climate variability and climate change. Qualitative analysis showed that Extension professionals recommended avoiding content related to politics, attribution of climate change to human causes, and telling farmers what to do. Respondents recommended emphasizing adaptation strategies, climate variability over climate change, evidence that climate change exists, and the financial benefits for farmers. In addition, Extension professionals proposed several delivery methods they thought would be most effective with farmers, including delivery tailored to the characteristics of the audience, a positive overall tone, and an understanding that engagement should be viewed as a long-term process based on building relationships with farmers. The findings suggest that farmers are a potentially receptive audience on climate issues when properly approached