1,355 research outputs found
The Effect of Hot Gas in WMAP's First Year Data
By cross-correlating templates constructed from the 2 Micron All Sky Survey
(2MASS) Extended Source (XSC) catalogue with WMAP's first year data, we search
for the thermal Sunyaev-Zel'dovich signature induced by hot gas in the local
Universe. Assuming that galaxies trace the distribution of hot gas, we select
regions on the sky with the largest projected density of galaxies. Under
conservative assumptions on the amplitude of foreground residuals, we find a
temperature decrement of -35 7 K ( detection level,
the highest reported so far) in the 26 square degrees of the sky
containing the largest number of galaxies per solid angle. We show that most of
the reported signal is caused by known galaxy clusters which, when convolved
with the average beam of the WMAP W band channel, subtend a typical angular
size of 20--30 arcmins. Finally, after removing from our analyses all pixels
associated with known optical and X-ray galaxy clusters, we still find a tSZ
decrement of -96 37 K in pixels subtending about 0.8 square
degrees on the sky. Most of this signal is coming from five different cluster
candidates in the Zone of Avoidance (ZoA), present in the Clusters In the ZoA
(CIZA) catalogue. We found no evidence that structures less bound than clusters
contribute to the tSZ signal present in the WMAP data.Comment: 10 pages, 4 figures, matches accepted version in ApJ Letter
On the Number Density of Sunyaev-Zel'dovich Clusters of Galaxies
If the mean properties of clusters of galaxies are well described by the
entropy-driven model, the distortion induced by the cluster population on the
blackbody spectrum of the Cosmic Microwave Background radiation is proportional
to the total amount of intracluster gas while temperature anisotropies are
dominated by the contribution of clusters of about 10^{14} solar masses. This
result depends marginally on cluster parameters and it can be used to estimate
the number density of clusters with enough hot gas to produce a detectable
Sunyaev-Zel'dovich effect. Comparing different cosmological models, the
relation depends mainly on the density parameter Omega_m. If the number density
of clusters could be estimated by a different method, then this dependence
could be used to constrain Omega_m.Comment: 8 pages, 3 figures, submitted to ApJ Letter
A sweet deal? Sugarcane, water and agricultural transformation in Sub-Saharan Africa
Globally, the area of sugarcane is rising rapidly in response to growing demands for bioethanol and increased sugar demand for human consumption. Despite considerable diversity in production systems and contexts, sugarcane is a particularly “high impact” crop with significant positive and negative environmental and socio-economic impacts. Our analysis is focused on Sub-Saharan Africa (SSA), which is a critical region for continued expansion, due to its high production potential, low cost of production and proximity, and access, to European markets. Drawing on a systematic review of scientific evidence, combined with information from key informants, stakeholders and a research-industry workshop, we critically assess the impacts of sugarcane development on water, soil and air quality, employment, food security and human health. Our analysis shows that sugarcane production is, in general, neither explicitly good nor bad, sustainable nor unsustainable. The impacts of expansion of sugarcane production on the environment and society depend on the global political economy of sugar, local context, quality of scheme, nature of the production system and farm management. Despite threats from climate change and forthcoming changes in the trade relationship with the European Union, agricultural development policies are driving national and international interest and investment in sugarcane in SSA, with expansion likely to play an important role in sustainable development in the region. Our findings will help guide researchers and policy makers with new insights in understanding the situated environmental and social impacts associated with alternative sugar economy models, production technologies and qualities of management
The galaxy cluster Ysz-Lx and Ysz-M relations from the WMAP 5-yr data
We use multifrequency matched filters to estimate, in the WMAP 5-year data,
the Sunyaev-Zel'dovich (SZ) fluxes of 893 ROSAT NORAS/REFLEX clusters spanning
the luminosity range Lx,[0.1-2.4]keV = 2 10^{41} - 3.5 10^{45} erg s^{-1}. The
filters are spatially optimised by using the universal pressure profile
recently obtained from combining XMM-Newton observations of the REXCESS sample
and numerical simulations. Although the clusters are individually only
marginally detected, we are able to firmly measure the SZ signal (>10 sigma)
when averaging the data in luminosity/mass bins. The comparison between the
bin-averaged SZ signal versus luminosity and X-ray model predictions shows
excellent agreement, implying that there is no deficit in SZ signal strength
relative to expectations from the X-ray properties of clusters. Using the
individual cluster SZ flux measurements, we directly constrain the Y500-Lx and
Y500-M500 relations, where Y500 is the Compton y-parameter integrated over a
sphere of radius r500. The Y500-M500 relation, derived for the first time in
such a wide mass range, has a normalisation Y*500=[1.60 pm 0.19] 10^{-3}
arcmin^2 at M500=3 10^{14} h^{1} Msun, in excellent agreement with the X-ray
prediction of 1.54 10^{-3} arcmin^2, and a mass exponent of alpha=1.79 pm 0.17,
consistent with the self-similar expectation of 5/3. Constraints on the
redshift exponent are weak due to the limited redshift range of the sample,
although they are compatible with self-similar evolution.Comment: Version accepted for publication in Astronomy and Astrophysic
Sonocrystallisation of ZIF-8 in water with high excess of ligand: Effects of frequency, power and sonication time
A systematic study on the sonocrystallisation of ZIF-8 (zeolitic imidazolate framework-8) in a water-based system was investigated under different mixing speeds, ultrasound frequencies, calorimetric powers and sonication time. Regardless of the synthesis technique, pure crystals of ZIF-8 with high BET (Brunauer, Emmett and Teller) specific surface area (SSA) can be obtained in water after only 5 s. Furthermore, 5 s sonication produced even smaller crystals (~0.08 µm). The type of technique applied for producing the ZIF-8 crystals did not have any significant impact on crystallinity, purity and yield. Crystal morphology and size were affected by the use of ultrasound and mixing, obtaining nanoparticles with a more spherical shape than in silent condition (no ultrasound and mixing). However, no specific trends were observed with varying frequency, calorimetric power and mixing speed. Ultrasound and mixing may have an effect on the nucleation step, causing the fast production of nucleation centres. Furthermore, the BET SSA increased with increasing mixing speed. With ultrasound, the BET SSA is between the values obtained under silent condition and with mixing. A competition between micromixing and shockwaves has been proposed when sonication is used for ZIF-8 production. The former increases the BET SSA, while the latter could be responsible for porosity damage, causing a decrease of the surface area. © 2021 The Author(s
The Sunyaev-Zeldovich effect in superclusters of galaxies using gasdynamical simulations: the case of Corona Borealis
[Abridged] We study the thermal and kinetic Sunyaev-Zel'dovich (SZ) effect
associated with superclusters of galaxies using the MareNostrum Universe SPH
simulation. We consider superclusters similar to the Corona Borealis
Supercluster (CrB-SC). This paper is motivated by the detection at 33GHz of a
strong temperature decrement in the CMB towards the core of this supercluster.
Multifrequency observations with VSA and MITO suggest the existence of a
thermal SZ effect component in the spectrum of this cold spot, which would
account for roughly 25% of the total observed decrement. We identify nine
regions containing superclusters similar to CrB-SC, obtain the associated SZ
maps and calculate the probability of finding such SZ signals arising from hot
gas within the supercluster. Our results show that WHIM produces a thermal SZ
effect much smaller than the observed value. Neither can summing the
contribution of small clusters and galaxy groups in the region explain the
amplitude of the SZ signal. When we take into account the actual posterior
distribution from the observations, the probability that WHIM can cause a
thermal SZ signal like the one observed is <1%, rising up to a 3.2% when the
contribution of small clusters and galaxy groups is included. If the
simulations provide a suitable description of the gas physics, then we conclude
that the thermal SZ component of the CrB spot most probably arises from an
unknown galaxy cluster along the line of sight. The simulations also show that
the kinetic SZ signal associated with the supercluster cannot provide an
explanation for the remaining 75% of the observed cold spot in CrB.Comment: Accepted for publication in MNRAS. 14 pages, 9 figure
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