562 research outputs found
On the signature of superclusters and voids in the Integrated Sachs-Wolfe effect
Through a large ensemble of Gaussian realisations and a suite of large-volume
N-body simulations, we show that in a standard LCDM scenario, supervoids and
superclusters in the redshift range should leave a {\em small}
signature on the ISW effect of the order K. We perform aperture
photometry on WMAP data, centred on such superstructures identified from SDSS
LRGs, and find amplitudes at the level of 8 -- 11K -- thus confirming the
earlier work of Granett et al 2008. If we focus on apertures of the size
\sim3.6\degr, then our realisations indicate that LCDM is discrepant at the
level of . If we combine all aperture scales considered, ranging
from 1\degr--20\degr, then the discrepancy becomes , and it
further lowers to if only 30 superstructures are considered
in the analysis (being compatible with no ISW signatures at in this
case). Full-sky ISW maps generated from our N-body simulations show that this
discrepancy cannot be alleviated by appealing to Rees-Sciama mechanisms, since
their impact on the scales probed by our filters is negligible. We perform a
series of tests on the WMAP data for systematics. We check for foreground
contaminants and show that the signal does not display the correct dependence
on the aperture size expected for a residual foreground tracing the density
field. The signal also proves robust against rotation tests of the CMB maps,
and seems to be spatially associated to the angular positions of the supervoids
and superclusters. We explore whether the signal can be explained by the
presence of primordial non-Gaussianities of the local type. We show that for
models with \FNL=\pm100, whilst there is a change in the pattern of
temperature anisotropies, all amplitude shifts are well below K.Comment: 14 pages, 9 figures, matches accepted version in MNRA
The clustering of merging star-forming haloes: dust emission as high frequency arcminute CMB foreground
Future observations of CMB anisotropies will be able to probe high multipole
regions of the angular power spectrum, corresponding to a resolution of a few
arcminutes. Dust emission from merging haloes is one of the foregrounds that
will affect such very small scales. We estimate the contribution to CMB angular
fluctuations from objects that are bright in the sub-millimeter band due to
intense star formation bursts following merging episodes. We base our approach
on the Lacey-Cole merger model and on the Kennicutt relation which connects the
star formation rate in galaxies with their infrared luminosity. We set the free
parameters of the model in order to not exceed the SCUBA source counts, the
Madau plot of star formation rate in the universe and COBE/FIRAS data on the
intensity of the sub-millimeter cosmic background radiation. We show that the
angular power spectrum arising from the distribution of such star-forming
haloes will be one of the most significant foregrounds in the high frequency
channels of future CMB experiments, such as PLANCK, ACT and SPT. The
correlation term, due to the clustering of multiple haloes at redshift z~2-6,
is dominant in the broad range of angular scales 200<l<3000. Poisson
fluctuations due to bright sub-millimeter sources are more important at higher
l, but since they are generated from the bright sources, such contribution
could be strongly reduced if bright sources are excised from the sky maps. The
contribution of the correlation term to the angular power spectrum depends
strongly on the redshift evolution of the escape fraction of UV photons and the
resulting temperature of the dust. The measurement of this signal will
therefore give important information about galaxies in the early stage of their
evolution.Comment: 18 pages, 16 figures. Accepted by Astronomy & Astrophysic
Sentido y significación de las TecnologÃas de la Información y la Comunicación para profesores de Educación Primaria. Resultados de investigación en Toluca, Estado de México
La relación entre la Educación y las TecnologÃas de la Información y la Comunicación como fenómeno pedagógico tiene una historia amplia y ricamente documentada, en la cual han concurrido diversos campos de conocimiento y cuyas miradas abordan diversas perspectivas que han dado cuenta de los aspectos que conciernen a los procesos de enseñanza y aprendizaje tecnológicamente mediados, a los aspectos polÃticos y administrativos que se implican con las necesidades, costos y evaluación de los beneficios de esta relación, a la proyección del alcance educativo, y también social y cultural del uso (o desuso) de los recursos tecnológicos disponibles por parte de docentes, alumnos, directivos y hasta padres de familia en las escuelas y fuera de ellas, entre otras problemáticas
Galaxy Clusters as mirrors of the distant Universe. Implications for the kSZ and ISW effects
It is well known that Thomson scattering of CMB photons in galaxy clusters
introduces new anisotropies in the CMB radiation field, but however little
attention is payed to the fraction of CMB photons that are scattered off the
line of sight, causing a slight blurring of the CMB anisotropies present at the
moment of scattering. In this work we study this {\it blurring} effect, and
find that it has a non-negligible impact on estimations of the kinetic
Sunyaev-Zel'dovich (kSZ) effect: it induces a 10% correction in 20-40% of the
clusters/groups, and a 100% correction in % of the clusters in an ideal
(noiseless) experiment. We explore the possibility of using this blurring term
to probe the CMB anisotropy field at different epochs in our Universe. In
particular, we study the required precision in the removal of the kSZ that
enables detecting the blurring term in galaxy cluster
populations placed at different redshift shells. By mapping this term in those
shells, we would provide a tomographic probe for the growth of the Integrated
Sachs Wolfe effect (ISW) during the late evolutionary stages of the Universe.
We find that the required precision of the cluster peculiar velocity removal is
of the order of 100 -- 200 km s in the redshift range 0.2 -- 0.8, after
assuming that all clusters more massive than 10 h M are
observable. These errors are comparable to the total expected linear line of
sight velocity dispersion for clusters in WMAPV cosmogony, and correspond to a
residual level of roughly 900 -- 1800 K per cluster, including all
types of contaminants and systematics. Were this precision requirement
achieved, then independent constraints on the intrinsic cosmological dipole
would be simultaneously provided.Comment: Notation clarified and typos and errors corrected in eqs.(2-4
Information and Communication Technologies in the Daily Life of Elementary School Teachers: An Attitudinal Framework
Within the framework of the inclusion of Information and Communication Technologies (ICTs) in primary education classrooms in the City of Toluca, State of Mexico, this research proposes an analysis on the social construction of meaning that teachers make about technology. The focus is mainly on the universe of meaning in which teachers relate to technology, for which it is sought to obtain from teachers a story about how ICT is meant by them.
This communication deals in particular with the element that precedes the possible action and thought around any entity in the universe of meaning: attitude. For the formation of our attitude towards an entity, favorable or not, positive or negative, a previous representation of it is required. The analysis is developed under the structure of three general indicators: What do you think about the technologies? Do you like to use technologies in your daily life? and Do you like to work with technologies
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