84 research outputs found
A Multiwavelength Photometric Census of AGN and Star Formation Activity in the Brightest Cluster Galaxies of X-ray Selected Clusters
Despite their reputation as being âred and deadâ, the unique environment inhabited by brightest cluster galaxies (BCGs) can often lead to a self-regulated feedback cycle between radiatively cooling intracluster gas and star formation and active galactic nucleus (AGN) activity in the BCG. However the prevalence of âactiveâ BCGs, and details of the feedback involved, are still uncertain. We have performed an optical, UV and mid-IR photometric analysis of the BCGs in 981 clusters at 0.03 < z < 0.5, selected from the ROSAT All Sky Survey. Using Pan-STARRS PS1 3Ï, GALEX and WISE survey data we look for BCGs with photometric colours which deviate from that of the bulk population of passive BCGs â indicative of AGN and/or star formation activity within the BCG. We find that whilst the majority of BCGs are consistent with being passive, at least 14âperâcent of our BCGs show a significant colour offset from passivity in at least one colour index. And, where available, supplementary spectroscopy reveals the majority of these particular BCGs show strong optical emission lines. On comparing BCG âactivityâ with the X-ray luminosity of the host cluster, we find that BCGs showing a colour offset are preferentially found in the more X-ray luminous clusters, indicative of the connection between BCG âactivityâ and the intracluster medium
How Coupling Determines the Entrainment of Circadian Clocks
Autonomous circadian clocks drive daily rhythms in physiology and behaviour.
A network of coupled neurons, the suprachiasmatic nucleus (SCN), serves as a
robust self-sustained circadian pacemaker. Synchronization of this timer to the
environmental light-dark cycle is crucial for an organism's fitness. In a
recent theoretical and experimental study it was shown that coupling governs
the entrainment range of circadian clocks. We apply the theory of coupled
oscillators to analyse how diffusive and mean-field coupling affects the
entrainment range of interacting cells. Mean-field coupling leads to amplitude
expansion of weak oscillators and, as a result, reduces the entrainment range.
We also show that coupling determines the rigidity of the synchronized SCN
network, i.e. the relaxation rates upon perturbation. %(Floquet exponents). Our
simulations and analytical calculations using generic oscillator models help to
elucidate how coupling determines the entrainment of the SCN. Our theoretical
framework helps to interpret experimental data
Chandra X-ray observations of the 3C295 cluster core
We examine the properties of the X-ray gas in the central regions of the
distant (z=0.46), X-ray luminous cluster of galaxies surrounding the powerful
radio source 3C 295, using observations made with the Chandra Observatory.
Between radii of 50-500 kpc, the cluster gas is approximately isothermal with
an emission-weighted temperature, kT ~5 keV. Within the central 50 kpc radius
this value drops to kT ~3.7 keV. The spectral and imaging Chandra data indicate
the presence of a cooling flow within the central 50 kpc radius of the cluster,
with a mass deposition rate of approximately 280 solar masses per year. We
estimate an age for the cooling flow of 1-2 Gyr, which is approximately one
thousand times older than the central radio source. We find no evidence in the
X-ray spectra or images for significant heating of the X-ray gas by the radio
source. We report the detection of an edge-like absorption feature in the
spectrum for the central 50 kpc region, which may be due to oxygen-enriched
dust grains. The implied mass in metals seen in absorption could have been
accumulated by the cooling flow over its lifetime. Combining the results on the
X-ray gas density profile with radio measurements of the Faraday rotation
measure in 3C295, we estimate the magnetic field strength in the region of the
cluster core to be B ~12 \muG.Comment: 27 pages, 16 figs, 5 tables. Accepted for publication in MNRA
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
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Atributos fĂsicos e matĂ©ria orgĂąnica de organossolos hĂĄplicos em distintos ambientes no Brasil
Cosmology with clusters of galaxies
In this Chapter I review the role that galaxy clusters play as tools to
constrain cosmological parameters. I will concentrate mostly on the application
of the mass function of galaxy clusters, while other methods, such as that
based on the baryon fraction, are covered by other Chapters of the book. Since
most of the cosmological applications of galaxy clusters rely on precise
measurements of their masses, a substantial part of my Lectures concentrates on
the different methods that have been applied so far to weight galaxy clusters.
I provide in Section 2 a short introduction to the basics of cosmic structure
formation. In Section 3 I describe the Press--Schechter (PS) formalism to
derive the cosmological mass function, then discussing extensions of the PS
approach and the most recent calibrations from N--body simulations. In Section
4 I review the methods to build samples of galaxy clusters at different
wavelengths. Section 5 is devoted to the discussion of different methods to
derive cluster masses. In Section 6 I describe the cosmological constraints,
which have been obtained so far by tracing the cluster mass function with a
variety of methods. Finally, I describe in Section 7 the future perspectives
for cosmology with galaxy clusters and the challenges for clusters to keep
playing an important role in the era of precision cosmology.Comment: 49 pages, 19 figures, Lectures for 2005 Guillermo Haro Summer School
on Clusters, to appear in "Lecture notes in Physics" (Springer
Comparação de métodos para estimar a acidez potencial mediante determinação do pH SMP em Organossolos da Serra do Espinhaço Meridional
Leaf nutrients, not specific leaf area, are consistent indicators of elevated nutrient inputs
Leaf traits are frequently measured in ecology to provide a âcommon currencyâ for predicting how anthropogenic pressures impact ecosystem function. Here, we test whether leaf traits consistently respond to experimental treatments across 27 globally distributed grassland sites across 4 continents. We find that specific leaf area (leaf area per unit mass)âa commonly measured morphological trait inferring shifts between plant growth strategiesâdid not respond to up to four years of soil nutrient additions. Leaf nitrogen, phosphorus and potassium concentrations increased in response to the addition of each respective soil nutrient. We found few significant changes in leaf traits when vertebrate herbivores were excluded in the short-term. Leaf nitrogen and potassium concentrations were positively correlated with species turnover, suggesting that interspecific trait variation was a significant predictor of leaf nitrogen and potassium, but not of leaf phosphorus concentration. Climatic conditions and pretreatment soil nutrient levels also accounted for significant amounts of variation in the leaf traits measured. Overall, we find that leaf morphological traits, such as specific leaf area, are not appropriate indicators of plant response to anthropogenic perturbations in grasslands
Soil net nitrogen mineralisation across global grasslands
Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important
for productivity and nutrient cycling. The balance between mineralisation and immobilisation
(net Nmin) varies with soil properties and climate. However, because most global-scale
assessments of net Nmin are laboratory-based, its regulation under field-conditions and
implications for real-world soil functioning remain uncertain. Here, we explore the drivers of
realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We
find that realised Nmin is largely explained by temperature of the wettest quarter, microbial
biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised
Nmin, but contributes to explain realised net Nmin when combined with soil and climatic
variables. We provide novel insights of global realised soil net Nmin and show that potential
soil net Nmin data available in the literature could be parameterised with soil and climate data
to better predict realised NNational Science Foundation Research Coordination Network;
Long-Term Ecological Research;
Institute on the Environment at the University of Minnesota.http://www.nature.com/ncommspm2020Mammal Research InstituteZoology and Entomolog
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