Multi-scale simulations of black hole accretion in barred galaxies: Self-gravitating disk models

Due to the non-axisymmetric potential of the central bar, barred spiral galaxies form, in addition to their characteristic arms and bar, a variety of structures within the thin gas disk, like nuclear rings, inner spirals and dust-lanes. These structures in the inner kiloparsec are most important to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conduct multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black-hole. We vary in all simulations the initial gas disk mass. As additional parameter we choose either the gas temperature for isothermal simulations or the cooling timescale in case of non-isothermal simulations. Accretion is either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk ($r< 300~\mathrm{pc}$) on the gas flow at kiloparsec scales. The final black hole masses reach up to $\sim 10^9 M_\odot$ after $1.6~\mathrm{Gyr}$. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit

The Minispiral in the Galactic Center revisited

We present the results of a re-examination of a [Ne II] line emission data cube (\lambda 12.8 \mu m) and discuss the kinematic structure of the inner \sim 3 \times 4 pc of the Galaxy. The quality of [Ne II] as a tracer of ionized gas is examined by comparing it to radio data. A three dimensional representation of the data cube allows us to disentangle features which are projected onto the same location on the sky. A model of gas streams in different planes is fitted to the data. We find that most of the material is located in a main plane which itself is defined by the inner edge of the Circum-Nuclear Disk in the Galactic Center. Finally, we present a possible three dimensional model of the gas streams.Comment: 12 pages, 18 figures; submitted to New Astronomy; higher resolution version and two animations available via anonymous ftp ftp://ftp.ita.uni-heidelberg.de/pub/ITA/wjd/Minispira

Regional resilience and fat tails: A stochastic analysis of firm growth rate distributions of German regions

This paper breaks down the distributional analysis of firm growth rates to the domain of regions. Extreme growth events, i.e. fat tails, are conceptualized as an indicator of competitive regional environments which enable processes like structural adaptation or technological re-orientation. An understanding of the heterogeneous dynamics at the level of firms, the 'turbulence underneath the big calm' (Dosi et al. 2012), provides a micro-funded empirical perspective on the evolutionary dimension of regional resilience. Therefore, the flexible Asymmetric Exponential Power (AEP) density is fitted to firm data for each German region during the years of economic downturn (2008-2010). Peculiarities of employment growth are explicitly taken into account by applying a new maximum likelihood estimation procedure with order statistics (Bottazzi 2012). The estimated parameters, which measure the tails' fatness, are then related to various region-specific factors that are discussed in the literature on regional resilience. Results show that firm growth rate distributions remain asymmetric and fat tailed at the spatially disaggregated level, but their shape markedly differ across regions. Extreme growth events, i.e. firm-level turbulences, are primarily a phenomenon of economically better performing regions at the aggregate level and further intensified by the presence of a higher qualified workforce. Besides, the fatness of the tails depends on the regions' industrial structure

La valoración de argumentaciones y explicaciones : promover estrategias de retroalimentación

This paper suggest focusing curriculum instruction and assessment models on the epistemic goals coupled with concept and perforpance goals. It discusses the design of learning environments that support students «doing science», in particular the role of assessment and the promotion of students development and evaluation of scientific claims

A Gravitational Instability-Driven Viscosity in Self-Gravitating Accretion Disks

We derive a viscosity from gravitational instability in self-gravitating accretion disks, which has the required properties to account for the observed fast formation of the first super-massive black holes in highly redshifted quasars and for the cosmological evolution of the black hole-mass distribution.Comment: 14 pages, 1 figure, ApJ Letters (in press