Impact of radiation feedback on the assembly of star clusters in galactic context

Massive star clusters are observed in a broad range of galaxy luminosity and types, and are assumed to form in dense gas-rich environments. Using a parsec-resolution hydrodynamical simulation of an isolated gas-rich low mass galaxy, we discuss here the non-linear effects of stellar feedback on the properties of star clusters with a focus on the progenitors of nuclear clusters. Our simulation shows two categories of star clusters: those for which feedback expels gas leftovers associated with their formation sites, and those, in a denser environment around which feedback fails at totally clearing the gas. We confirm that radiation feedback (photo-ionization and radiative pressure) plays a more important role than type-II supernovae in destroying dense gas structures, and altering or quenching the subsequent cluster formation. It also disturbs the cluster mass growth, by increasing the internal energy of the gas component to the point when radiation pressure overcomes the cluster gravity. We discuss how these effects may depend on the local properties of the interstellar medium, and also on the details of the subgrid recipes, which can affect the available cluster gas reservoirs, the evolution of potential nuclear clusters progenitors, and the overall galaxy morphology.Comment: 10 pages, 7 Figures, MNRAS accepte

Understanding, defining and measuring the trait of superstition.

Superstitious beliefs influence a wide range of decisions and activities in the everyday life. Yet, superstition has received little attention in the consumer behaviour literature, which is surprising since superstitious behaviours are found in numerous related domains, such as sports (Schippers & Lange, 2006), gambling or travelling. In the psychological and sociological literature, there is no consensus regarding the definition and measure of superstition (Mowen & Carlson, 2003). For some authors, superstition includes all types of paranormal beliefs (i.e. religion, astrology…) which we think are not relevant for superstition construct. Other authors have a very narrow definition of superstition restricting it to popular beliefs such as (black cats bring bad luck; if you break a mirror, you will have bad luck; the number 13 is unlucky”). The aim of this research is threefold: (1) to better define the superstition construct (2) to develop a scale that measures superstition and (3) to discuss the interest of superstition for marketing. An exploratory qualitative study allowed us to define superstition as “beliefs and/or practices that have no religious nor scientific foundations and which lead people to think that certain facts (external events or one’s own actions), or objects can bring good or bad luck, or be signs announcing positive or negative consequences”. Three quantitative data collections helped us develop a scale that contains 27 items and 5 dimensions (good fortune popular beliefs a = 0,84 ; misfortune popular beliefs a = 0,85 ; belief in destiny a = 0,83 ; magical thinking a = 0,86 ; defensive pessimism a = 0,67). Finally, the article concludes on future research and how the superstition construct could help explain irrational decision making.Consumer behavior; Superstition; marketing; échelle de mesure;

Exploring ways to estimate endogenous productivity

This paper explores methods to assess the impact on firm productivity of the investment in innovation activities (endogenous productivity). It uses 23 years of firm-level data generated by the Spanish ESEE survey (1990-2012). We first apply traditional approaches to the measurement of productivity such as Solow Residual and Multilateral Index. We then replicate the estimation of the model in Doraszelski and Jaumandreu (2013) using more data now available. We briefly compare both approaches and discuss about the importance of treating inputs and productivity as endogenous. We then discuss ways to apply the model for endogenous productivity when there are no firm-level output price indices available, a limitation of many data bases. Including the demand of the firm in the estimation allows us to obtain a "composite" of productivity, demand elasticity, and demand heterogeneity. This unobservable, often called "revenue productivity", is the estimate of productivity used by most scholarly studies. We find that this composite does not behave as productivity and, in particular, neither is greater for firms that perform R&D nor its distribution shows stochastic dominance. Its persistence and returns also give misleading results. Our findings highlight the importance of producing more complete databases, especially if policy implications are to be drawn. They also suggest caution in interpreting the results based on revenue productivity

The Taylor principle and global determinacy in a non Ricardian world

The Taylor principle is quite usually considered as a central condition for price determinacy. Recently, however, this has been questioned on several grounds, notably because (i) this condition is a condition for local determinacy, not global determinacy (ii) it has been derived in "Ricardian" economies, and it appears that going to a non-Ricardian framework makes a very big difference for the determinacy conditions. In this paper we scrutinize the two issues together, and we find that for non-Ricardian equilibria the Taylor principle is replaced by another "financial dominance" criterion.Taylor principle ; Taylor rules ; global determinacy ; price determinacy ; non Ricardian economies ; non Ricardian equilibria

Are Cosmological Gas Accretion Streams Multiphase and Turbulent?

Simulations of cosmological filamentary accretion reveal flows ("streams") of warm gas, ~$10^4$ K, which are efficient in bringing gas into galaxies. We present a phenomenological scenario where gas in such flows -- if it is shocked as it enters the halo as we assume -- become biphasic and, as a result, turbulent. We consider a collimated stream of warm gas that flows into a halo from an over dense filament of the cosmic web. The post-shock streaming gas expands because it has a higher pressure than the ambient halo gas, and fragments as it cools. The fragmented stream forms a two phase medium: a warm cloudy phase embedded in hot post-shock gas. We argue that the hot phase sustains the accretion shock. A fraction of the initial kinetic energy of the infalling gas is converted into turbulence among and within the warm clouds. The thermodynamic evolution of the post-shock gas is largely determined by the relative timescales of several processes -- the cooling, the expansion of the post-shock gas, the amount of turbulence in the clouds, and the halo dynamics. We expect the gas to become multiphase when the cooling and dynamical times are of the same order-of-magnitude. In this framework, we show that this occurs in the important mass range of ~$10^{11}$ to $10^{13}$ M$_\odot$ , where the bulk of stars have formed in galaxies. Gas accreting along cosmic web filaments may eventually lose coherence and mix with the ambient halo gas. Through both the phase separation and "disruption" of the stream, the accretion efficiency onto a galaxy in a halo dynamical time is lowered. De-collimating flows make the direct interaction between galaxy feedback and accretion streams more likely, thereby further reducing the overall accretion efficiency. Moderating the gas accretion efficiency through these mechanisms may help to alleviate a number of significant challenges in theoretical galaxy formation.Comment: 13 pages, 8 figures, Submitted to A&A, New version includes new figure

On the behavior of upwind schemes in the low Mach number limit. IV : P0 Approximation on triangular and tetrahedral cells

Finite Volume upwind schemes for the Euler equations in the low Mach number regime face a problem of lack of convergence toward the solutions of the incompressible system. However, if applied to cell centered triangular grid, this problem disappears and convergence toward the incompressible solution is recovered. We give here a general proof of this fact for arbitrary unstructured meshes. In addition, we also show that this result is equally valid for unstructured three dimensional tetrahedral meshes

ANTARES sensitivity to steady cosmic gamma ray sources

International audienceAmongst the atmospheric muons recorded by neutrino telescopes are muons produced by the interaction of cosmic gamma rays with the Earth's atmosphere. Although they are not numerous, it has been suggested that such muons could be distinguished by neutrino telescopes from the isotropic background by correlating their direction with known sources of gamma rays. The ANTARES neutrino telescope is taking data at the bottom of the Mediterranean Sea in its full configuration since May 2008. Its expected sensitivity to steady gamma ray sources is discussed, as well as the gamma ray induced neutrino contamination of cosmic neutrino signals. It is shown that the expected signal from steady gamma ray sources is well below the ANTARES detection ability, and that gamma rays are a negligible source of atmospheric neutrinos background