625 research outputs found
Anisotropy Studies of the Unresolved Far-infrared Background
Dusty, starforming galaxies and active galactic nuclei that contribute to the
integrated background intensity at far-infrared wavelengths trace the
large-scale structure. Below the point source detection limit, correlations in
the large-scale structure lead to clustered anisotropies in the unresolved
component of the far-infrared background (FIRB). The angular power spectrum of
the FIRB anisotropies could be measured in large-area surveys with the Spectral
and Photometric Imaging Receiver (SPIRE) on the upcoming Herschel observatory.
To study statistical properties of these anisotropies, the confusion from
foreground Galactic dust emission needs to be reduced even in the ``cleanest''
regions of the sky.The multi-frequency coverage of SPIRE allows the foreground
dust to be partly separated from the extragalactic background composed of dusty
starforming galaxies as well as faint normal galaxies. The separation improves
for fields with sizes greater than a few hundred square degrees and when
combined with Planck data. We show that an area of about 400 degrees
observed for about 1000 hours with Herschel-SPIRE and complemented by Planck
provides maximal information on the anisotropy power spectrum. We discuss the
scientific studies that can be done with measurements of the unresolved FIRB
anisotropies including a determination of the large scale bias and the
small-scale halo occupation distribution of FIRB sources with fluxes below the
point-source detection level.Comment: 10 pages, 8 figures, replaced to match the extended version, accepted
by Ap
Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours
We present colourâcolour diagrams of detected sources in the Herschel-ATLAS science demonstration field from 100 to 500 ÎŒm using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3Ï, we find an average dust temperature of (28±8) K. For sources with no known redshift, we populate the colourâcolour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 ÎŒm and detected at 250 and 500 ÎŒm with a significance greater than 3Ï, we find an average redshift of 2.2 ± 0.6
The social fabric of Jeans': Assessing the social: Coupling social simulation and assessment methods
International audienceThe culture and manufacturing of the cotton fabric used to make your Jeansâ may have implied the use of fertilizers or pesticides polluting a water basin, have led to relocating people and even of children labour at different stages of its fabrication. As a consumer you probably didnât take all these consequences into account (for your sake most of the information is not available, or value-wise you feel unconcerned) and you surely preferred to buy the cheapest one or to follow the fashion trend. Basically, every economic or public activity has repercussions directly, or through a chain of consequences on the environment and the society. In order to try and measure those impacts, or to valuate one choice (Jeansâ L) compared to another (Jeansâ P&J), several assessment methods have been developed and are frequently used. As a self-evident truth, assessment methods are instruments used to evaluate something. These could include measuring a performance on a specific case. In terms of evaluating policies and strategies, their possible outcomes are intended to evaluate their potential impacts. This refers to impact assessment in which past (already implemented actions) or future (ex-ante analysis) performances are studied
CMB Constraints on Primordial non-Gaussianity from the Bispectrum (f_{NL}) and Trispectrum (g_{NL} and \tau_{NL}) and a New Consistency Test of Single-Field Inflation
We outline the expected constraints on non-Gaussianity from the cosmic
microwave background (CMB) with current and future experiments, focusing on
both the third (f_{NL}) and fourth-order (g_{NL} and \tau_{NL}) amplitudes of
the local configuration or non-Gaussianity. The experimental focus is the
skewness (two-to-one) and kurtosis (two-to-two and three-to-one) power spectra
from weighted maps. In adition to a measurement of \tau_{NL} and g_{NL} with
WMAP 5-year data, our study provides the first forecasts for future constraints
on g_{NL}. We describe how these statistics can be corrected for the mask and
cut-sky through a window function, bypassing the need to compute linear terms
that were introduced for the previous-generation non-Gaussianity statistics,
such as the skewness estimator. We discus the ratio A_{NL} =
\tau_{NL}/(6f_{NL}/5)^2 as an additional test of single-field inflationary
models and discuss the physical significance of each statistic. Using these
estimators with WMAP 5-Year V+W-band data out to l_{max}=600 we constrain the
cubic order non-Gaussianity parameters \tau_{NL}, and g_{NL} and find -7.4 <
g_{NL}/10^5 < 8.2 and -0.6 < \tau_{NL}/10^4 < 3.3 improving the previous
COBE-based limit on \tau_{NL} < 10^8 nearly four orders of magnitude with WMAP.Comment: 15 pages. 14 figure
Submillimetre galaxies reside in dark matter haloes with masses greater than 3âĂâ10^(11) solar masses
The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum
of brightness fluctuations at 250, 350 and 500 ”m. From this excess, we find that submillimetre galaxies are located in darkmatter haloes with a minimum mass, M_(min), such that log_(10)[M_(min)/M_â] = 11.5^(+0.7)_(-0.2) at 350 ”m, where M_â is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation
Structure of microbial communities in Sphagnum peatlands and effect of atmospheric carbon dioxide enrichment
Little is known about the structure of microbial communities in Sphagnum peatlands, and the potential effects of the increasing atmospheric C02 concentration on these communities are not known. We analyzed the structure of microbial communities in five Sphagnum-dominated peatlands across Europe and their response to C02 enrichment using miniFACE systems. After three growing seasons, Sphagnum samples were analyzed for heterotrophic bacteria, cyanobacteria, microalgae, heterotrophic flagellates, ciliates, testate amoebae, fungi, nematodes, and rotifers. Heterotrophic organisms dominated the microbial communities and together represented 78% to 97% of the total microbial biomass. Testate amoebae dominated the protozoan biomass. A canonical correspondence analysis revealed a significant correlation between the microbial community data and four environmental variables (Na+, DOC, water table depth, and DIN), reflecting continentality, hydrology, and nitrogen deposition gradients. Carbon dioxide enrichment modified the structure of microbial communities, but total microbial biomass was unaffected. The biomass of heterotrophic bacteria increased by 48%, and the biomass of testate amoebae decreased by 13%. These results contrast with the absence of overall effect on methane production or on the vegetation, but are in line with an increased below-ground vascular plant biomass at the same sites. We interpret the increase in bacterial biomass as a response to a C02-induced enhancement of Sphagnum exudation. The causes for the decrease of testate amoebae are unclear but could indicate a top-down rather than a bottom-up control on their densit
Impact of Point Source Clustering on Cosmological Parameters with CMB Anisotropies
The faint radio point sources that are unresolved in cosmic microwave
background (CMB) anisotropy maps are likely to be a biased tracer of the
large-scale structure dark matter distribution. While the shot-noise
contribution to the angular power spectrum of unresolved radio point sources is
included either when optimally constructing the CMB angular power spectrum, as
with WMAP data, or when extracting cosmological parameters, we suggest that
clustering part of the point source power spectrum should also be included.
This is especially necessary at high frequencies above 150 GHz, where the
clustering of far-IR sources is expected to dominate the shot-noise level of
the angular power spectrum at tens of arcminute angular scales of both radio
and sub-mm sources. We make an estimate of source clustering of unresolved
radio sources in both WMAP and ACBAR, and marginalize over the amplitude of
source clustering in each CMB data set when model fitting for cosmological
parameters. For the combination of WMAP 5-year data and ACBAR, we find that the
spectral index changes from the value of to
(at 68% c.l.) when the clustering power spectrum of point sources is included
in model fits. While we find that the differences are marginal with and without
source clustering in current data, it may be necessary to account for source
clustering with future datasets such as Planck, especially to properly model
fit anisotropies at arcminute angular scales. If clustering is not accounted
and point sources are modeled with a shot-noise only out to , the
spectral index will be biased by about 1.5.Comment: 10 pages, 7 figure
Structure of microbial communities in Sphagnum peatlands and effect of atmospheric carbon dioxide enrichment
Mobility and Social Network Effects on Extremist Opinions
Understanding the emergence of extreme opinions and in what kind of
environment they might become less extreme is a central theme in our modern
globalized society. A model combining continuous opinions and observed discrete
actions (CODA) capable of addressing the important issue of measuring how
extreme opinions might be has been recently proposed. In this paper I show
extreme opinions to arise in a ubiquitous manner in the CODA model for a
multitude of social network structures. Depending on network details reducing
extremism seems to be possible. However, a large number agents with extreme
opinions is always observed. A significant decrease in the number of extremists
can be observed by allowing agents to change their positions in the network.Comment: 7 pages, 8 figures, discussion expanded, new references, new figure
Needlet Detection of Features in WMAP CMB Sky and the Impact on Anisotropies and Hemispherical Asymmetries
We apply spherical needlets to the Wilkinson Microwave Anisotropy Probe
5-year cosmic microwave background (CMB) dataset, to search for imprints of
non-isotropic features in the CMB sky. We use the needlets localization
properties to resolve peculiar features in the CMB sky and to study how these
features contribute to the anisotropy power spectrum of the CMB. In addition to
the now well-known "cold spot" of the CMB map in the southern hemisphere, we
also find two hot spots at greater than 99% confidence level, again in the
southern hemisphere and closer to the Galactic plane. While the cold spot
contributes to the anisotropy power spectrum in the multipoles between l=6 to
l=33, the hot spots are found to be dominating the anisotropy power in the
range between l=6 and l=18. Masking both the cold and the two hot spots results
in a reduction by about 15% in the amplitude of the angular power spectrum of
CMB around l=10. The resulting changes to the cosmological parameters when the
power spectrum is estimated masking these features (in addition to the WMAP
team's KQ85 mask) are within the 1 errors published with the WMAP mask
only. We also study the asymmetry between the angular power spectra evaluated
on the northern and southern hemispheres. When the features detected by
needlets are masked, we find that the difference in the power, measured in
terms of the anisotropy variance between l=4 and l=18, is reduced by a factor
2. We make available a mask related to needlet features for more detailed
studies on asymmetries in the CMB anisotropy sky.Comment: 12 pages, 12 figures; masks available at
http://www.fisica.uniroma2.it/~cosmo/mask
- âŠ