Three-dimensional simulations of a starburst wind

In order to better understand the formation of a starburst-driven wind, we have performed a series of three-dimensional hydrodynamical simulations in an inhomogeneous interstellar medium. We present the results of these simulations, which provide new insights into the formation of the optical filaments and the origin of the soft X-ray emission

Three-Dimensional Simulations of a Starburst-Driven Galactic Wind

We have performed a series of three-dimensional simulations of a starburst-driven wind in an inhomogeneous interstellar medium. The introduction of an inhomogeneous disk leads to differences in the formation of a wind, most noticeably the absence of the ``blow-out'' effect seen in homogeneous models. A wind forms from a series of small bubbles that propagate into the tenuous gas between dense clouds in the disk. These bubbles merge and follow the path of least resistance out of the disk, before flowing freely into the halo. Filaments are formed from disk gas that is broken up and accelerated into the outflow. These filaments are distributed throughout a biconical structure within a more spherically distributed hot wind. The distribution of the inhomogeneous interstellar medium in the disk is important in determining the morphology of this wind, as well as the distribution of the filaments. While higher resolution simulations are required in order to ascertain the importance of mixing processes, we find that soft X-ray emission arises from gas that has been mass-loaded from clouds in the disk, as well as from bow shocks upstream of clouds, driven into the flow by the ram pressure of the wind, and the interaction between these shocks.Comment: 37 pages, 16 figures, mpg movie can be obtained at http://www.mso.anu.edu.au/~jcooper/movie/video16.mpg, accepted for publication in Ap

HOW TO ASK FOR GOOD GOVERNMENT

Summary Good government matters, and should be asked for. But it is mistaken to suppose that it necessarily consists pursuing a particular policy to realize a particular outcome in conditions of competitive democracy. Good government is not best thought of in terms of the outcomes of policy or as satisfying one kind of constitutional or institutional condition rather than another. It is that government which is best suited in the circumstances to maximizing the benefits of social cooperation. States, it is argued here, have a contract to provide it, and this is the contract to which donors should hold them. The article defends this view and sketches some if its implications. Résumé Le bon gouvernement est une chose de la plus grande importance; aussi faut?il savoir le réclamer. Or l'on aurait tort de supposer que le bon gouvernement ait pour seul objet de poursuivre telle ou telle politique dans l'optique d'arriver à tel ou tel résultat dans le cadre d'une démocratie compétitive. Le bon gouvernement ne s'exprime ni en termes des résultats de telle ou telle politique, ni en termes de la satisfaction d'une condition constitutionnelle ou institutionnelle à la place d'une autre. La bon gouvernement consiste à obtenir la meilleure adaptation possible aux circonstances en vigueur, dans le contexte de la maximalisation des avantages de la coopération sociale. Selon l'article, les états s'engagent contractuellement à fournir le bon gouvernement; et c'est à ce contrat que les donateurs devraient les tenir. L'article défend ce point de vue et esquisse certaines des implications qui en découlent. Resumen El buen gobierno importa, y debe ser exigido. Pero es un error suponer que éste consiste necesariamente en seguir una política determinada para alcanzar un resultado determinado en condiciones de democracia competitiva. No se debe pensar en el buen gobierno en función de las consecuencias de los programas políticos o de satisfacer una u otra condición constitucional o institucional. Este tipo de gobierno es el más apropiado en las presentes circunstancias para potenciar los beneficios de la cooperación social. Se argumenta que los países tienen un contrato para proveerla, y que los donantes deben exigir que se atengan a él. El artículo defiende esta posición y bosqueja algunas de sus implicaciones

Starburst-Driven Galactic Winds: Filament Formation and Emission Processes

We have performed a series of three-dimensional simulations of the interaction of a supersonic wind with a non-spherical radiative cloud. These simulations are motivated by our recent three-dimensional model of a starburst-driven galactic wind interacting with an inhomogeneous disk, which show that an optically emitting filament can be formed by the break-up and acceleration of a cloud into a supersonic wind. In this study we consider the evolution of a cloud with two different geometries (fractal and spherical) and investigate the importance of radiative cooling on the cloud's survival. We have also undertaken a comprehensive resolution study in order to ascertain the effect of the assumed numerical resolution on the results. We find that the ability of the cloud to radiate heat is crucial for its survival. While an adiabatic cloud is destroyed over a short period of time, a radiative cloud is broken up via the Kelvin-Helmholtz instability into numerous small, dense cloudlets, which are drawn into the flow to form a filamentary structure. The degree of fragmentation is highly dependent on the resolution of the simulation, with the number of cloudlets formed increasing as the Kelvin-Helmholtz instability is better resolved. Nevertheless, there is a clear qualitative trend, with the filamentary structure still persistent at high resolution. We confirm the mechanism behind the formation of the H-alpha emitting filaments found in our global simulations of a starburst-driven wind. Based on our resolution study, we conclude that bow shocks around accelerated gas clouds, and their interaction, are the main source of the soft X-ray emission observed in these galactic-scale winds. [ABRIDGED]Comment: Accepted to ApJ, 39 pages, 21 figures, movie file can obtained at http://www.mso.anu.edu.au/~jcooper/movie/halpha.mo

Interview with Geoffrey Hawthorn on Malthus and population

A training film for undergraduates using very early equipment. The interview was conducted by Sofka ZinovieffAn interview with the sociologist Geoffrey Hawthorn in relation to Malthus and population, made in 1985 as part of the materials for the film 'The Mountebank Parson' made by Sofka Zinovieff, Rachel Riley and John Bell in that yea

Interview with Geoffrey Hawthorn on Malthus and population

A training film for undergraduates using very early equipment. the interview was conducted by Sofka ZinovieffAn interview with Geoffrey Hawthorn in relation to Malthus and population, made in 1985 as part of the materials for the film 'The Mountebank Parson' by Sofka Zinovieff, Rachel Riley and John Bell in that yea

Population and development : High and low fertility in poorer countries

210 p; 23 c

An interview of Geoffrey Hawthorn

Filmed by Alan Macfarlane on 23rd April 2009 and edited by Sarah HarrisonAn interview of Professor Geoffrey Hawthorn about his life and work