Ram pressure stripping in a viscous intracluster medium

In the recent literature there is circumstantial evidence that the viscosity of the intracluster medium may not be too far from the Spitzer value. In this letter, we present two-dimensional hydrodynamical simulations of ram pressure stripping of disc galaxies in a viscous intracluster medium. The values of viscosity explored range between 0.1 and 1.0 times the Spitzer value. We find that viscosity affects the appearance and the dimensions of the galactic wakes but has very little effect on the evolution of the gas mass of the galaxy.Comment: 5 pages, 2 figures, accepted by MNRAS letter

The Stringency of Environmental Regulation and the 'Porter Hypothesis'

Most empirical evidence indicates that the costs of environmental regulation represent a minor fraction of total production costs. This finding is at odds with the assumption of stringent environmental regulation of both propo-nents and opponents of the ''Porter Hypothesis''. A possible explanation may be provided by examining the nego-tiation of environmental regulation in a ''political market''. In this market, stakeholder attempt to ensure their pre-ferred level of stringency through influencing political decision makers. In most cases, the equilibrium stringency will require pollution abatement levels that can be met with best available technology (BAT) or predictable ad-vances over BAT. Accordingly, net benefits from environmental regulation as claimed by a ''strong version'' of the ''Porter Hypothesis'' are unlikely to emerge. On the other hand, competitiveness is equally unlikely to suffer. How-ever, compliance may impose disproportionate costs on technological laggards. The argument is illustrated with evidence from a study on the techno-economic consequences of Austrian VOC emission standards.economics of technology ;

Some micro-evidence on the "Porter Hypothesis" from Austrian VOC emission standards

In the context of the discussion on the 'Porter Hypothesis', a sizeable amount of research has been devoted to empirical tests of the impact of environmental regulation on both competitiveness and innovation. The standard practice is to regress some measure of regulatory stringency on some measure of competitiveness and innovation across several industries and/or countries. However, possibly due to measurement problems, the results of these studies tend to be inconclusive and if any effects are found, these are usually rather small. Addressing the measurement problem, this paper uses highly disaggregated foreign trade data and data from a full survey of the Austrian paint, coatings, printing inks and adhesive industry to examine the impact of Austrian VOC emission standards on Austrian manufacturers of the regulated products. These standards are particularly interesting in that they are the most restrictive of their kind in the world and therefore an excellent case to study some of the issues raised by the 'Porter Hypothesis'. Based on various measures of RCA, I find no impact (i.e. neither negative nor positive) on competitiveness, which is also supported by the industry's own evaluation in the survey. I do find, however, that the regulations restricted imports. An important corollary of this finding is that the industry's current attempt to have the more restrictive Austrian regulation relaxed to the more lenient provisions of the European VOC directive may be counterproductive, since contrary to popular belief this may increase import competition rather than facilitate exports. Second, I consider various indicators of innovation based on evidence from the survey. I find that the regulation induced sizeable changes of firms' product range which vary by technological sub-segment. These changes are also reflected in a more dynamic technological environment. R&D spending to develop compliant products is found to be very unevenly distributed. While some firms spent virtually nothing, other firms devoted almost their complete R&D budget to compliance innovations. This result is mainly a function of technology and to a lesser extent of organisational factors. Moreover, there is evidence that the introduction of compliant products displaced or postponed existing R&D projects, again with substantial variations by technology. Finally, the survey produces evidence that compliance efforts yielded new ideas and allowed some firms to acquire new competencies and technologies, which they would not have acquired in the absence of the regulation. However, the latter finding is most probably due to technologically backward (small) firms catching up. To summarise, the survey evidence reveals considerable heterogeneity in how firms were affected and responded to the regulation. Partly, this is an expected result of a uniform command-and-control regulation, partly it indicates a differential ability of firms to adapt to an external shock. Although based on a very small sample, the paper points to interesting lines of enquiry that should be explored in future research.

Cold fronts: probes of plasma astrophysics in galaxy clusters

The most massive baryonic component of galaxy clusters is the “intracluster medium” (ICM), a diffuse, hot, weakly magnetized plasma that is most easily observed in the X-ray band. Despite being observed for decades, the macroscopic transport properties of the ICM are still not well-constrained. A path to determine macroscopic ICM properties opened up with the discovery of “cold fronts”. These were observed as sharp discontinuities in surface brightness and temperature in the ICM, with the property that the denser side of the discontinuity is the colder one. The high spatial resolution of the Chandra X-ray Observatory revealed two puzzles about cold fronts. First, they should be subject to Kelvin-Helmholtz instabilities, yet in many cases they appear relatively smooth and undisturbed. Second, the width of the interface between the two gas phases is typically narrower than the mean free path of the particles in the plasma, indicating negligible thermal conduction. It was thus realized that these special characteristics of cold fronts may be used to probe the properties of the cluster plasma. In this review, we will discuss the recent simulations of cold fronts in galaxy clusters, focusing on those which have attempted to use these features to constrain ICM physics. In particular, we will examine the effects of magnetic fields, viscosity, and thermal conductivity on the stability properties and long-term evolution of cold fronts. We conclude with a discussion on what important questions remain unanswered, and the future role of simulations and the next generation of X-ray observatories

On the Uncertainties of Stellar Mass Estimates via Colour Measurements

Mass-to-light versus colour relations (MLCRs), derived from stellar population synthesis models, are widely used to estimate galaxy stellar masses (M$_*$) yet a detailed investigation of their inherent biases and limitations is still lacking. We quantify several potential sources of uncertainty, using optical and near-infrared (NIR) photometry for a representative sample of nearby galaxies from the Virgo cluster. Our method for combining multi-band photometry with MLCRs yields robust stellar masses, while errors in M$_*$ decrease as more bands are simultaneously considered. The prior assumptions in one's stellar population modelling dominate the error budget, creating a colour-dependent bias of up to 0.6 dex if NIR fluxes are used (0.3 dex otherwise). This matches the systematic errors associated with the method of spectral energy distribution (SED) fitting, indicating that MLCRs do not suffer from much additional bias. Moreover, MLCRs and SED fitting yield similar degrees of random error ($\sim$0.1-0.14 dex) when applied to mock galaxies and, on average, equivalent masses for real galaxies with M$_* \sim$ 10$^{8-11}$ M$_{\odot}$. The use of integrated photometry introduces additional uncertainty in M$_*$ measurements, at the level of 0.05-0.07 dex. We argue that using MLCRs, instead of time-consuming SED fits, is justified in cases with complex model parameter spaces (involving, for instance, multi-parameter star formation histories) and/or for large datasets. Spatially-resolved methods for measuring M$_*$ should be applied for small sample sizes and/or when accuracies less than 0.1 dex are required. An Appendix provides our MLCR transformations for ten colour permutations of the $grizH$ filter set.Comment: Accepted to MNRAS. 43 pages, 12 figures, 3 table

Fast simulations of gas sloshing and cold front formation

We present a simplified and fast method for simulating minor mergers between galaxy clusters. Instead of following the evolution of the dark matter halos directly by the N-body method, we employ a rigid potential approximation for both clusters. The simulations are run in the rest frame of the more massive cluster and account for the resulting inertial accelerations in an optimised way. We test the reliability of this method for studies of minor merger induced gas sloshing by performing a one-to-one comparison between our simulations and hydro+N-body ones. We find that the rigid potential approximation reproduces the sloshing-related features well except for two artefacts: the temperature just outside the cold fronts is slightly over-predicted, and the outward motion of the cold fronts is delayed by typically 200 Myr. We discuss reasons for both artefacts.Comment: 14 pages, 15 figures. Accepted by MNRA

Ram pressure stripping of disc galaxies orbiting in clusters. I. Mass and radius of the remaining gas disc

We present the first 3D hydrodynamical simulations of ram pressure stripping of a disc galaxy orbiting in a galaxy cluster. Along the orbit, the ram pressure that this galaxy experiences varies with time. In this paper, we focus on the evolution of the radius and mass of the remaining gas disc and compare it with the classical analytical estimate proposed by Gunn & Gott 1972. We find that this simple estimate works well in predicting the evolution of the radius of the remaining gas disc. Only if the ram pressure increases faster than the stripping timescale, the disc radius remains larger than predicted. However, orbits with such short ram pressure peaks are unlikely to occur in other than compact clusters. Unlike the radius evolution, the mass loss history for the galaxy is not accurately described by the analytical estimate. Generally, in the simulations the galaxy loses its gas more slowly than predicted.Comment: 11 pages, 11 figures, accepted by MNRAS, high resolution pdf version available at http://www.faculty.iu-bremen.de/eroediger/PAPERS/eroediger_crossing.pd

Does technology affect network structure? - A quantitative analysis of collaborative research projects in two specific EU programmes

The promotion of collaborative R&D through Framework Programmes is a top priority of European RTD policy. However, despite the considerable sums involved, surprisingly little is known about the structure of the resulting research networks. Arguing that the underlying technological regime critically affects the structure of collaborative R&D, this article examines the structure and topology of collaborative research networks in the telecommunications and the agro-industrial industry in two specific programmes of the 4th EU Framework Programme. We find systematic differences which we attribute to differences in the underlying knowledge base, the research trajectories pursued in EU-funded R&D and the organisation of knowledge production in the two industries. As expected on the basis of prior research, we show that collaborative research projects involve a larger number of partners and require greater funding in the telecommunications industry, and that actors from science are positioned more prominently in the agro-industrial collaborative R&D network. Contrary to expectations, we find fewer and less intense interactions between science and industry in the agro-industrial industry. We provide a tentative explanation for this result and discuss policy implications.framework programmes, research collaborations, technological regime, sectoral innovation system, social network analysis, science-industry interactions