Spanish National Research Council

About: Spanish National Research Council is a government organization based out in Madrid, Spain. It is known for research contribution in the topics: Population & Galaxy. The organization has 79563 authors who have published 220470 publications receiving 7698991 citations. The organization is also known as: CSIC & Consejo Superior de Investigaciones Científicas.

The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations

Abstract: We present results from thirteen cosmological simulations that explore the parameter space of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) simulation project. Four of the simulations follow the evolution of a periodic cube L = 50 cMpc on a side, and each employs a different subgrid model of the energetic feedback associated with star formation. The relevant parameters were adjusted so that the simulations each reproduce the observed galaxy stellar mass function at z = 0.1. Three of the simulations fail to form disc galaxies as extended as observed, and we show analytically that this is a consequence of numerical radiative losses that reduce the efficiency of stellar feedback in high-density gas. Such losses are greatly reduced in the fourth simulation - the EAGLE reference model - by injecting more energy in higher density gas. This model produces galaxies with the observed size distribution, and also reproduces many galaxy scaling relations. In the remaining nine simulations, a single parameter or process of the reference model was varied at a time. We find that the properties of galaxies with stellar mass <~ M* (the "knee" of the galaxy stellar mass function) are largely governed by feedback associated with star formation, while those of more massive galaxies are also controlled by feedback from accretion onto their central black holes. Both processes must be efficient in order to reproduce the observed galaxy population. In general, simulations that have been calibrated to reproduce the low-redshift galaxy stellar mass function will still not form realistic galaxies, but the additional requirement that galaxy sizes be acceptable leads to agreement with a large range of observables.

Community assembly, coexistence and the environmental filtering metaphor

Abstract: Summary One of the most pervasive concepts in the study of community assembly is the metaphor of the environmental filter, which refers to abiotic factors that prevent the establishment or persistence of species in a particular location. The metaphor has its origins in the study of community change during succession and in plant community dynamics, although it has gained considerable attention recently as part of a surge of interest in functional trait and phylogenetic-based approaches to the study of communities. While the filtering metaphor has clear utility in some circumstances, it has been challenging to reconcile the environmental filtering concept with recent developments in ecological theory related to species coexistence. These advances suggest that the evidence used in many studies to assess environmental filtering is insufficient to distinguish filtering from the outcome of biotic interactions. We re-examine the environmental filtering metaphor from the perspective of coexistence theory. In an effort to move the discussion forward, we present a simple framework for considering the role of the environment in shaping community membership, review the literature to document the evidence typically used in environmental filtering studies and highlight research challenges to address in coming years. The current usage of the environmental filtering term in empirical studies likely overstates the role abiotic tolerances play in shaping community structure. We recommend that the term ‘environmental filtering’ only be used to refer to cases where the abiotic environment prevents establishment or persistence in the absence of biotic interactions, although only 15% of the studies in our review presented such evidence. Finally, we urge community ecologists to consider additional mechanisms aside from environmental filtering by which the abiotic environment can shape community pattern.

Asymmetric coevolutionary networks facilitate biodiversity maintenance

Abstract: The mutualistic interactions between plants and their pollinators or seed dispersers have played a major role in the maintenance of Earth's biodiversity. To investigate how coevolutionary interactions are shaped within species-rich communities, we characterized the architecture of an array of quantitative, mutualistic networks spanning a broad geographic range. These coevolutionary networks are highly asymmetric, so that if a plant species depends strongly on an animal species, the animal depends weakly on the plant. By using a simple dynamical model, we showed that asymmetries inherent in coevolutionary networks may enhance long-term coexistence and facilitate biodiversity maintenance.

Late-time cosmology in (phantom) scalar-tensor theory: dark energy and the cosmic speed-up

Abstract: We consider late-time cosmology in a (phantom) scalar-tensor theory with an exponential potential, as a dark energy model with equation of state parameter close to -1 (a bit above or below this value). Scalar (and also other kinds of) matter can be easily taken into account. An exact spatially-flat FRW cosmology is constructed for such theory, which admits (eternal or transient) acceleration phases for the current universe, in correspondence with observational results. Some remarks on the possible origin of the phantom, starting from a more fundamental theory, are also made. It is shown that quantum gravity effects may prevent (or, at least, delay or soften) the cosmic doomsday catastrophe associated with the phantom, i.e. the otherwise unavoidable finite-time future singularity (Big Rip). A novel dark energy model (higher-derivative scalar-tensor theory) is introduced and it is shown to admit an effective phantom/quintessence description with a transient acceleration phase. In this case, gravity favors that an initially insignificant portion of dark energy becomes dominant over the standard matter/radiation components in the evolution process.