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Kuntschner H.,European Southern Observatory | Emsellem E.,European Southern Observatory | Cappellari M.,University of Oxford | Davies R.L.,University of Oxford | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present a stellar population analysis of the absorption line strength maps for 48 early-type galaxies from the SAURON sample. Using the line strength index maps of Hβ, Fe5015 and Mg b, measured in the Lick/IDS system and spatially binned to a constant signal-to-noise ratio, together with predictions from up-to-date stellar population models, we estimate the simple stellar population-equivalent (SSP-equivalent) age, metallicity and abundance ratio [alpha;/Fe] over a two-dimensional field extending up to approximately one effective radius. A discussion of calibrations and differences between model predictions is given. Maps of SSP-equivalent age, metallicity and abundance ratio [alpha;/Fe] are presented for each galaxy. We find a large range of SSP-equivalent ages in our sample, of which ~40 per cent of the galaxies show signs of a contribution from a young stellar population. The most extreme cases of post-starburst galaxies, with SSP-equivalent ages of ≤3 Gyr observed over the full field-of-view, and sometimes even showing signs of residual star formation, are restricted to low-mass systems (σe≤ 100 km s-1 or ~2 × 1010 M.). Spatially restricted cases of young stellar populations in circumnuclear regions can almost exclusively be linked to the presence of star formation in a thin, dusty disc/ring, also seen in the near-UV or mid-IR on top of an older underlying stellar population.The flattened components with disc-like kinematics previously identified in all fast rotators are shown to be connected to regions of distinct stellar populations. These range from the young, still star-forming circumnuclear discs and rings with increased metallicity preferentially found in intermediate-mass fast rotators, to apparently old structures with extended disc-like kinematics, which are observed to have an increased metallicity and mildly depressed [alpha;/Fe] ratio compared to the main body of the galaxy. The slow rotators, often harbouring kinematically decoupled components (KDC) in their central regions, generally show no stellar population signatures over and above the well-known metallicity gradients in early-type galaxies and are largely consistent with old (≥10 Gyr) stellar populations.Using radially averaged stellar population gradients we find in agreement with Spolaor et al. a mass-metallicity gradient relation where low-mass fast rotators form a sequence of increasing metallicity gradient with increasing mass. For more massive systems (above ~3.5 × 1010 M.) there is an overall downturn such that metallicity gradients become shallower with increased scatter at a given mass leading to the most massive systems being slow rotators with relatively shallow metallicity gradients. The observed shallower metallicity gradients and increased scatter could be a consequence of the competition between different star formation and assembly scenarios following a general trend of diminishing gas fractions and more equal-mass mergers with increasing mass, leading to the most massive systems being devoid of ordered motion and signs of recent star formation. © 2010 The Authors. Journal compilation © 2010 RAS.

Milone A.P.,Institute Astrofsica Of Canarias | Milone A.P.,University of La Laguna | Marino A.F.,Max Planck Institute for Astrophysics | Piotto G.,University of Padua | And 7 more authors.
Astrophysical Journal | Year: 2012

High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC6397 splits into two components, containing 30% and 70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing 30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance (ΔY 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m F336W. Theoretical isochrones indicate that this could be due to NH depletion. © 2012. The American Astronomical Society. All rights reserved.

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.

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.

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.

Ramsay G.,Armagh Observatory | Doyle J.G.,Armagh Observatory | Hakala P.,University of Turku | Garcia-Alvarez D.,Institute Astrofsica Of Canarias | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Using data obtained during the RATS-Kepler project, we identified one short-duration flare in a 1 h sequence of ground-based photometry of the dwarf star KIC 5474065. Observations made using Gran Telescopio Canarias show that it is a star with an M4V spectral type. Kepler observations made using 1 min sampling show that KIC 5474065 exhibits large-amplitude (δF/F > 0.4) optical flares which have a duration as short as 10 min. We compare the energy distribution of flares from KIC 5474065 with that of KIC 9726699, which has also been observed using 1-min sampling, and ground-based observations of other M dwarf stars in the literature. We discuss the possible implications these short-duration, relatively low-energy flares would have on the atmosphere of exoplanets orbiting in the habitable zone of these flare stars. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Honig S.F.,University of California at Santa Barbara | Kishimoto M.,Max Planck Institute for Radio Astronomy | Antonucci R.,University of California at Santa Barbara | Marconi A.,University of Florence | And 3 more authors.
Astrophysical Journal | Year: 2012

Advancements in infrared (IR) interferometry open up the possibility to spatially resolve active galactic nuclei (AGNs) on the parsec-scale level and study the circumnuclear dust distribution, commonly referred to as the "dust torus," that is held responsible for the type 1/type 2 dichotomy of AGNs. We used the mid-IR beam combiner MIDI together with the 8m telescopes at the Very Large Telescope Interferometer to observe the nucleus of the Seyfert 2 galaxy NGC424, achieving an almost complete coverage of the uv-plane accessible by the available telescope configurations. We detect extended mid-IR emission with a relatively baseline- and model-independent mid-IR half-light radius of (2.0 ± 0.2) pc × (1.5 ± 0.3) pc (averaged over the 8-13 μm wavelength range). The extended mid-IR source shows an increasing size with wavelength. These properties are in agreement with the idea of dust heated in thermal equilibrium with the AGN. The orientation of the major axis in position angle - 27° is closely aligned with the system axis as set by optical polarization observations. Torus models typically favor extension along the mid-plane at mid-IR wavelengths instead. Therefore, we conclude that the majority of the parsec-scale mid-IR emission (≳60%) in this type 2 AGN originates from optically thin dust in the polar region of the AGN, a scenario consistent with the near- to far-IR spectral energy distribution. We suggest that a radiatively driven dusty wind, possibly launched in a puffed-up region of the inner hot part of the torus, is responsible for the polar dust. In this picture, the torus dominates the near-IR emission up to about 5 μm, while the polar dust is the main contributor to the mid-IR flux. Our results of NGC424 are consistent with recent observations of the AGN in the Circinus galaxy and resemble large-scale characteristics of other objects. If our results reflect a general property of the AGN population, the current paradigm for interpreting and modeling the IR emission of AGNs has to be revised. © 2012. The American Astronomical Society. All rights reserved.

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..

Elmegreen D.M.,Vassar College | Elmegreen B.G.,IBM | Sanchez Almeida J.,Institute Astrofsica Of Canarias | Munoz-Tunon C.,Institute Astrofsica Of Canarias | And 3 more authors.
Astrophysical Journal | Year: 2012

Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use Sloan Digital Sky Survey data to determine the ages, masses, and surface densities of the heads and tails in 14local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with rest-frame galaxy luminosity, ranging from ∼105 Ṁ at galaxy absolute magnitude U = -13mag to 109 Ṁ at U = -20mag. The corresponding head surface density increases from several M ̇pc-2 locally to 10-100 Ṁpc -2 at high redshift, and the star formation rate (SFR) per unit area in the head increases from ∼0.01 Ṁyr-1kpc -2 locally to ∼1 Ṁyr-1kpc-2 at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological SFRs, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far-outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size. © © 2012. The American Astronomical Society. All rights reserved..

Elmegreen B.G.,IBM | Elmegreen D.M.,Vassar College | Sanchez Almeida J.,Institute Astrofsica Of Canarias | Munoz-Tunon C.,Institute Astrofsica Of Canarias | And 6 more authors.
Astrophysical Journal | Year: 2013

Local UV-bright galaxies in the Kiso survey include clumpy systems with kiloparsec-size star complexes that resemble clumpy young galaxies in surveys at high redshift. We compare clump masses and underlying disks in several dozen galaxies from each of these surveys to the star complexes and disks of normal spirals. Photometry and spectroscopy for the Kiso and spiral sample come from the Sloan Digital Sky Survey. We find that the largest Kiso clumpy galaxies resemble Ultra Deep Field (UDF) clumpies in terms of the star formation rates, clump masses, and clump surface densities. Clump masses and surface densities in normal spirals are smaller. If the clump masses are proportional to the turbulent Jeans mass in the interstellar medium, then for the most luminous galaxies in the sequence of normal:Kiso:UDF, the turbulent speeds and surface densities increase in the proportions 1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe B-band absolute magnitude. For the least luminous galaxies in the overlapping magnitude range, the turbulent speed and surface density trends are 1.0:2.7:7.4 and 1.0:1.4:3.0, respectively. We also find that while all three types have radially decreasing disk intensities when measured with ellipse-fit azimuthal averages, the average profiles are more irregular for UDF clumpies (which are viewed in their restframe UV) than for Kiso galaxies (viewed at g-band), and major axis intensity scans are even more irregular for the UDF than Kiso galaxies. Local clumpy galaxies in the Kiso survey appear to be intermediate between UDF clumpies and normal spirals. © 2013. The American Astronomical Society. All rights reserved.

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