401 research outputs found
A first estimate of radio halo statistics from large-scale cosmological simulation
We present a first estimate based on a cosmological gasdynamics simulation of
galaxy cluster radio halo counts to be expected in forthcoming low-frequency
radio surveys. Our estimate is based on a FLASH simulation of the LCDM model
for which we have assigned radio power to clusters via a model that relates
radio emissivity to cluster magnetic field strength, intracluster turbulence,
and density. We vary several free parameters of this model and find that radio
halo number counts vary by up to a factor of two for average magnetic fields
ranging from 0.2 to 3.1 uG. However, we predict significantly fewer
low-frequency radio halos than expected from previous semi-analytic estimates,
although this discrepancy could be explained by frequency-dependent radio halo
probabilities as predicted in reacceleration models. We find that upcoming
surveys will have difficulty in distinguishing models because of large
uncertainties and low number counts. Additionally, according to our modeling we
find that expected number counts can be degenerate with both reacceleration and
hadronic secondary models of cosmic ray generation. We find that relations
between radio power and mass and X-ray luminosity may be used to distinguish
models, and by building mock radio sky maps we demonstrate that surveys such as
LOFAR may have sufficient resolution and sensitivity to break this model
degeneracy by imaging many individual clusters.Comment: 18 pages, 14 figures, revised from referee comments, ApJ accepted,
public catalog available at
http://sipapu.astro.illinois.edu/http://sipapu.astro.illinois.edu/foswiki/bin/view/Main/RadioHaloMap
Fenotipagem de plantas de cupuaçuzeiro obtidas da população contrastante para resistência a Moniliophtora perniciosa.
Comparative analysis of the diffuse radio emission in the galaxy clusters A1835, A2029, and Ophiuchus
We recently performed a study of a sample of relaxed, cooling core galaxy
clusters with deep Very Large Array observations at 1.4 GHz. We find that in
the central regions of A1835, A2029, and Ophiuchus the dominant radio galaxy is
surrounded by a diffuse low-brightness radio emission that takes the form of a
mini-halo. Here we present the results of the analysis of the extended diffuse
radio emission in these mini-halos. In order to investigate the morphological
properties of the diffuse radio emission in clusters of galaxies we propose to
fit their azimuthally averaged brightness profile with an exponential,
obtaining the central brightness and the e-folding radius from which the radio
emissivity can be calculated. We investigate the radio properties of the
mini-halos in A1835, A2029, and Ophiuchus in comparison with the radio
properties of a representative sample of mini-halos and halos already known in
the literature. We find that radio halos can have quite different length-scales
but their emissivity is remarkably similar from one halo to the other. In
contrast, mini-halos span a wide range of radio emissivity. Some of them, like
the Perseus mini-halos, are characterized by a radio emissivity which is more
than 100 times greater than that of radio halos. On the other hand, the new
mini-halos in cooling core clusters analyzed in this work, namely A2029,
Ophiuchus, and A1835, have a radio emissivity which is much more typical of
halos in merging clusters rather than similar to that of the other mini-halos
previously known.Comment: 17 pages, 11 figures, A&A in press. For a version with high quality
figures, see http://erg.ca.astro.it/preprints/mini_halo_2
Prospects of detecting gamma-ray emission from galaxy clusters: cosmic rays and dark matter annihilations
We study the possibility for detecting gamma-ray emission from galaxy
clusters. We consider 1) leptophilic models of dark matter (DM) annihilation
that include a Sommerfeld enhancement (SFE), 2) different representative
benchmark models of supersymmetric DM, and 3) cosmic ray (CR) induced pion
decay. Among all clusters/groups of a flux-limited X-ray sample, we predict
Virgo, Fornax and M49 to be the brightest DM sources and find a particularly
low CR-induced background for Fornax. For a minimum substructure mass given by
the DM free-streaming scale, cluster halos maximize the substructure boost for
which we find a factor above 1000. Since regions around the virial radius
dominate the annihilation flux of substructures, the resulting surface
brightness profiles are almost flat. This makes it very challenging to detect
this flux with imaging atmospheric Cherenkov telescopes. Assuming cold dark
matter with a substructure mass distribution down to an Earth mass and using
extended Fermi upper limits, we rule out the leptophilic models in their
present form in 28 clusters, and limit the boost from SFE in M49 and Fornax to
be < 5. This corresponds to a limit on SFE in the Milky Way of < 3, which is
too small to account for the increasing positron fraction with energy as seen
by PAMELA and challenges the DM interpretation. Alternatively, if SFE is
realized in Nature, this would imply a limiting substructure mass of M_lim >
10^4 M_sol - a problem for structure formation. Using individual cluster
observations, it will be challenging for Fermi to constrain our selection of DM
benchmark models without SFE. The Fermi upper limits are, however, closing in
on our predictions for the CR flux using an analytic model based on
cosmological hydrodynamical cluster simulations. We limit the CR-to-thermal
pressure in nearby bright galaxy clusters of the Fermi sample to < 10% and in
Norma and Coma to < 3%.Comment: 43 pages, 23 figures, 10 tables. Accepted for publication in Phys.
Rev. D: streamlined paper, added a paragraph about detectability to
introduction, few references added, and few typos correcte
Avaliação de clones de cupuaçuzeiro em ambiente de pesquisa participativa.
A elevada variabilidade fenotĂpica observada nos plantios comerciais do Estado do Pará, proporciona uma excelente oportunidade para seleção de materiais superiores. Há necessidade de identificar as matrizes potencialmente promissoras nos pomares comerciais, multiplica-las e avalia-las em delineamento experimental, para definir as que verdadeiramente apresentam caracterĂsticas genotĂpicas para serem aproveitadas nos programas de melhoramento do cupuaçuzeiro. O objetivo desta pesquisa foi avaliar matrizes de cupuaçuzeiro, multiplicadas vegetativamente, em um ambiente de pesquisa participativa, visando identificar materiais promissores e adaptados Ă s condições do Estado do Pará. Foram testados 25 clones originários de matrizes identificadas em pomares comerciais do municĂpio de TomĂ© Açu. O experimento foi instalado no delineamento experimental de blocos casualizados, com 25 tratamentos e cinco repetições com trĂŞs plantas na parcela. Foram coletados dados de desenvolvimento vegetativo inicial, nĂşmero de frutos produzidos por planta em quatro safras, bem como, plantas afetadas pela vassoura de bruxa. Os resultados revelaram grande variabilidade entre os clones, tanto para desenvolvimento vegetativo quanto para a produção de frutos. Alguns materiais tiveram comportamento destacado como o clone 7, seguido pelos clones 4, 3, 6, 15, 24, 25, 9, 14 e 17. Ficaram tambĂ©m evidenciadas as vantagens da parceria com o setor produtivo, em pesquisas dessa natureza.PIBIC-2011
Chandra Observations of Abell 85: Merger of the South Subcluster
We present an analysis of a highly asymmetric cluster merger from a Chandra
observation of Abell 85. The merger shows significant disruption of the less
massive subcluster from ram pressure effects. Nevertheless, a cold core,
coincident with the cD galaxy, is observed to persist in the subcluster. We
derive dynamical information from the motion of the cold core through the main
cluster's ICM. Multiple derivations of the velocity of the core suggest a Mach
number of M ~ 1.4 or v ~ 2150 km/s, though with substantial uncertainty. We
construct a consistent kinematic model for the merger based on this dynamical
analysis. As has been found for other such "cold fronts," conduction appears to
be suppressed across the front. Thermal conduction may be suppressed by a
magnetic field with a significant component perpendicular to the subcluster's
direction of motion. The effect of the merger interaction in creating and
shaping the observed radio sources is also discussed. It appears most likely
that the radio source is due to distorted and detached lobes from the
subcluster cD galaxy, rather than being a radio halo.Comment: Accepted for publication in ApJ. 10 pages, 9 figures (3 color), uses
emulateapj5. For version with high resolution figures, see
http://www.astro.virginia.edu/~jck7k/research/papers/A85_south.ps.g
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