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Trayford J.W.,Durham University | Theuns T.,Durham University | Bower R.G.,Durham University | Schaye J.,Leiden University | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We calculate the colours and luminosities of redshift z=0.1 galaxies from the EAGLE simulation suite using the GALAXEV population synthesis models. We take into account obscuration by dust in birth clouds and diffuse interstellar medium using a two-component screen model, following the prescription of Charlot and Fall. We compare models in which the dust optical depth is constant to models where it depends on gas metallicity, gas fraction and orientation. The colours of EAGLE galaxies for the more sophisticated models are in broad agreement with those of observed galaxies. In particular, EAGLE produces a red sequence of passive galaxies and a blue cloud of star-forming galaxies, with approximately the correct fraction of galaxies in each population and with g-r colourswithin 0.1mag of those observed. Luminosity functions from ultraviolet to near-infrared wavelengths differ from observations at a level comparable to systematic shifts resulting from a choice between Petrosian and Kron photometric apertures. Despite the generally good agreement there are clear discrepancies with observations. The blue cloud of EAGLE galaxies extends to somewhat higher luminosities than in the data, consistent with the modest underestimate of the passive fraction in massive EAGLE galaxies. There is also a moderate excess of bright blue galaxies compared to observations. The overall level of agreement with the observed colour distribution suggests that EAGLE galaxies at z = 0.1 have ages, metallicities and levels of obscuration that are comparable to those of observed galaxies. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Mazeh T.,Tel Aviv University | Mazeh T.,Institute Astrofsica Of Canarias | Holczer T.,Tel Aviv University | Shporer A.,California Institute of Technology | Shporer A.,Jet Propulsion Laboratory
Astrophysical Journal | Year: 2015

Some transiting planets discovered by the Kepler mission display transit timing variations (TTVs) induced by stellar spots that rotate on the visible hemisphere of their parent stars. An induced TTV can be observed when a planet crosses a spot and modifies the shape of the transit light curve, even if the time resolution of the data does not allow the detection of the crossing event itself. We present an approach that can, in some cases, use the derived TTVs of a planet to distinguish between a prograde and a retrograde planetary motion with respect to the stellar rotation. Assuming a single spot darker than the stellar disk, spot crossing by the planet can induce measured positive (negative) TTV, if the crossing occurs in the first (second) half of the transit. On the other hand, the motion of the spot toward (away from) the center of the stellar visible disk causes the stellar brightness to decrease (increase). Therefore, for a planet with prograde motion, the induced TTV is positive when the local slope of the stellar flux at the time of transit is negative, and vice versa. Thus, we can expect to observe a negative (positive) correlation between the TTVs and the photometric slopes for prograde (retrograde) motion. Using a simplistic analytical approximation, and also the publicly available SOAP-T tool to produce light curves of transits with spot-crossing events, we show for some cases how the induced TTVs depend on the local stellar photometric slopes at the transit timings. Detecting this correlation in Kepler transiting systems with high enough signal-to-noise ratio can allow us to distinguish between prograde and retrograde planetary motions. In upcoming papers we present analyses of the KOIs and Kepler eclipsing binaries, following the formalism developed here. © 2015. The American Astronomical Society. All rights reserved.. Source

Laken B.A.,Institute Astrofsica Of Canarias | Laken B.A.,University of La Laguna | Calogovic J.,University of Zagreb
Journal of Space Weather and Space Climate | Year: 2013

The composite (superposed epoch) analysis technique has been frequently employed to examine a hypothesized link between solar activity and the Earth's atmosphere, often through an investigation of Forbush decrease (Fd) events (sudden high-magnitude decreases in the flux cosmic rays impinging on the upper-atmosphere lasting up to several days). This technique is useful for isolating low-amplitude signals within data where background variability would otherwise obscure detection. The application of composite analyses to investigate the possible impacts of Fd events involves a statistical examination of time-dependent atmospheric responses to Fds often from aerosol and/or cloud datasets. Despite the publication of numerous results within this field, clear conclusions have yet to be drawn and much ambiguity and disagreement still remain. In this paper, we argue that the conflicting findings of composite studies within this field relate to methodological differences in the manner in which the composites have been constructed and analyzed. Working from an example, we show how a composite may be objectively constructed to maximize signal detection, robustly identify statistical significance, and quantify the lower-limit uncertainty related to hypothesis testing. Additionally, we also demonstrate how a seemingly significant false positive may be obtained from non-significant data by minor alterations to methodological approaches. © B.A. Laken et al., Published by EDP Sciences 2013. © B.A. Laken et al., Published by EDP Sciences 2013. Source

Paardekooper J.-P.,University of Heidelberg | Paardekooper J.-P.,Max Planck Institute for Extraterrestrial Physics | Khochfar S.,University of Edinburgh | Vecchia C.D.,Institute Astrofsica Of Canarias | Vecchia C.D.,University of La Laguna
Monthly Notices of the Royal Astronomical Society | Year: 2015

Protogalaxies forming in low-mass dark matter haloes are thought to provide the majority of ionizing photons needed to reionize the Universe, due to their high escape fractions of ionizing photons. We study how the escape fraction in high-redshift galaxies relates to the physical properties of the halo in which the galaxies form, by computing escape fractions in more than 75 000 haloes between redshifts 27 and 6 that were extracted from the First Billion Years project, high-resolution cosmological hydrodynamical simulations of galaxy formation. We find that the main constraint on the escape fraction is the gas column density in a radius of 10 pc around the stellar populations, causing a strong mass dependence of the escape fraction. The lower potential well in haloes with M200 ≲ 108 M results in low column densities that can be penetrated by radiation from young stars (age <5 Myr). In haloes with M200 ≳ 108 M supernova feedback is important, but only ~30 per cent of the haloes in this mass range have an escape fraction higher than 1 per cent. We find a large range of escape fractions in haloes with similar properties, caused by different distributions of the dense gas in the halo. This makes it very hard to predict the escape fraction on the basis of halo properties and results in a highly anisotropic escape fraction. The strong mass dependence, the large spread and the large anisotropy of the escape fraction may strongly affect the topology of reionization and is something current models of cosmic reionization should strive to take into account. © 2015 The Authors. Source

Furlong M.,Durham University | Bower R.G.,Durham University | Theuns T.,Durham University | Theuns T.,University of Antwerp | And 11 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We investigate the evolution of galaxy masses and star formation rates in the Evolution and Assembly of Galaxies and their Environment (EAGLE) simulations. These comprise a suite of hydrodynamical simulations in a Λ cold dark matter cosmogony with subgrid models for radiative cooling, star formation, stellar mass-loss and feedback from stars and accreting black holes. The subgrid feedback was calibrated to reproduce the observed present-day galaxy stellar mass function and galaxy sizes. Here, we demonstrate that the simulations reproduce the observed growth of the stellar mass density to within 20 per cent. The simulations also track the observed evolution of the galaxy stellar mass function out to redshift z = 7, with differences comparable to the plausible uncertainties in the interpretation of the data. Just as with observed galaxies, the specific star formation rates of simulated galaxies are bimodal, with distinct star forming and passive sequences. The specific star formation rates of star-forming galaxies are typically 0.2 to 0.5 dex lower than observed, but the evolution of the rates track the observations closely. The unprecedented level of agreement between simulation and data across cosmic time makes EAGLE a powerful resource to understand the physical processes that govern galaxy formation. © 2015 The Authors. Source

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