762 research outputs found
Sunyaev-Zel'dovich profiles and scaling relations: modelling effects and observational biases
We use high-resolution hydrodynamic re-simulations to investigate the
properties of the thermal Sunyaev-Zel'dovich (SZ) effect from galaxy clusters.
We compare results obtained using different physical models for the
intracluster medium (ICM), and show how they modify the SZ emission in terms of
cluster profiles and scaling relations. We also produce realistic mock
observations to verify whether the results from hydrodynamic simulations can be
confirmed. We find that SZ profiles depend marginally on the modelled physical
processes, while they exhibit a strong dependence on cluster mass. The central
and total SZ emission strongly correlate with the cluster X-ray luminosity and
temperature. The logarithmic slopes of these scaling relations differ from the
self-similar predictions by less than 0.2; the normalization of the relations
is lower for simulations including radiative cooling. The observational test
suggests that SZ cluster profiles are unlikely to be able to probe the ICM
physics. The total SZ decrement appears to be an observable much more robust
than the central intensity, and we suggest using the former to investigate
scaling relations.Comment: 13 pages, 12 figures, accepted by MNRA
Correlated Component Analysis for diffuse component separation with error estimation on simulated Planck polarization data
We present a data analysis pipeline for CMB polarization experiments, running
from multi-frequency maps to the power spectra. We focus mainly on component
separation and, for the first time, we work out the covariance matrix
accounting for errors associated to the separation itself. This allows us to
propagate such errors and evaluate their contributions to the uncertainties on
the final products.The pipeline is optimized for intermediate and small scales,
but could be easily extended to lower multipoles. We exploit realistic
simulations of the sky, tailored for the Planck mission. The component
separation is achieved by exploiting the Correlated Component Analysis in the
harmonic domain, that we demonstrate to be superior to the real-space
application (Bonaldi et al. 2006). We present two techniques to estimate the
uncertainties on the spectral parameters of the separated components. The
component separation errors are then propagated by means of Monte Carlo
simulations to obtain the corresponding contributions to uncertainties on the
component maps and on the CMB power spectra. For the Planck polarization case
they are found to be subdominant compared to noise.Comment: 17 pages, accepted in MNRA
Model Independent Foreground Power Spectrum Estimation using WMAP 5-year Data
In this paper, we propose & implement on WMAP 5-year data, a model
independent approach of foreground power spectrum estimation for multifrequency
observations of CMB experiments. Recently a model independent approach of CMB
power spectrum estimation was proposed by Saha et al. 2006. This methodology
demonstrates that CMB power spectrum can be reliably estimated solely from WMAP
data without assuming any template models for the foreground components. In the
current paper, we extend this work to estimate the galactic foreground power
spectrum using the WMAP 5 year maps following a self contained analysis. We
apply the model independent method in harmonic basis to estimate the foreground
power spectrum and frequency dependence of combined foregrounds. We also study
the behaviour of synchrotron spectral index variation over different regions of
the sky. We compare our results with those obtained from MEM foreground maps
which are formed in pixel space. We find that relative to our model independent
estimates MEM maps overestimates the foreground power close to galactic plane
and underestimates it at high latitudes.Comment: 12 pages, 4 figure
Anomalous Microwave Emission from the HII region RCW175
We present evidence for anomalous microwave emission in the RCW175 \hii
region. Motivated by 33 GHz 13\arcmin resolution data from the Very Small
Array (VSA), we observed RCW175 at 31 GHz with the Cosmic Background Imager
(CBI) at a resolution of 4\arcmin. The region consists of two distinct
components, G29.0-0.6 and G29.1-0.7, which are detected at high signal-to-noise
ratio. The integrated flux density is Jy at 31 GHz, in good
agreement with the VSA. The 31 GHz flux density is Jy
() above the expected value from optically thin free-free emission
based on lower frequency radio data and thermal dust constrained by IRAS and
WMAP data. Conventional emission mechanisms such as optically thick emission
from ultracompact \hii regions cannot easily account for this excess. We
interpret the excess as evidence for electric dipole emission from small
spinning dust grains, which does provide an adequate fit to the data.Comment: 5 pages, 2 figures, submmited to ApJ Letter
Bacterial RuBisCO Is Required for Efficient Bradyrhizobium/Aeschynomene Symbiosis
Rhizobia and legume plants establish symbiotic associations resulting in the formation of organs specialized in nitrogen fixation. In such organs, termed nodules, bacteria differentiate into bacteroids which convert atmospheric nitrogen and supply the plant with organic nitrogen. As a counterpart, bacteroids receive carbon substrates from the plant. This rather simple model of metabolite exchange underlies symbiosis but does not describe the complexity of bacteroids' central metabolism. A previous study using the tropical symbiotic model Aeschynomene indica/photosynthetic Bradyrhizobium sp. ORS278 suggested a role of the bacterial Calvin cycle during the symbiotic process. Herein we investigated the role of two RuBisCO gene clusters of Bradyrhizobium sp. ORS278 during symbiosis. Using gene reporter fusion strains, we showed that cbbL1 but not the paralogous cbbL2 is expressed during symbiosis. Congruently, CbbL1 was detected in bacteroids by proteome analysis. The importance of CbbL1 for symbiotic nitrogen fixation was proven by a reverse genetic approach. Interestingly, despite its symbiotic nitrogen fixation defect, the cbbL1 mutant was not affected in nitrogen fixation activity under free living state. This study demonstrates a critical role for bacterial RuBisCO during a rhizobia/legume symbiotic interaction
Gravitational-wave astronomy: the high-frequency window
This contribution is divided in two parts. The first part provides a
text-book level introduction to gravitational radiation. The key concepts
required for a discussion of gravitational-wave physics are introduced. In
particular, the quadrupole formula is applied to the anticipated
``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300:
inspiralling compact binaries. The second part provides a brief review of high
frequency gravitational waves. In the frequency range above (say) 100Hz,
gravitational collapse, rotational instabilities and oscillations of the
remnant compact objects are potentially important sources of gravitational
waves. Significant and unique information concerning the various stages of
collapse, the evolution of protoneutron stars and the details of the
supranuclear equation of state of such objects can be drawn from careful study
of the gravitational-wave signal. As the amount of exciting physics one may be
able to study via the detections of gravitational waves from these sources is
truly inspiring, there is strong motivation for the development of future
generations of ground based detectors sensitive in the range from hundreds of
Hz to several kHz.Comment: 21 pages, 5 figures, Lectures presented at the 2nd Aegean Summer
School on the Early Universe, Syros, Greece, September 200
Substructures in hydrodynamical cluster simulations
The abundance and structure of dark matter subhalos has been analyzed
extensively in recent studies of dark matter-only simulations, but
comparatively little is known about the impact of baryonic physics on halo
substructures. We here extend the SUBFIND algorithm for substructure
identification such that it can be reliably applied to dissipative
hydrodynamical simulations that include star formation. This allows, in
particular, the identification of galaxies as substructures in simulations of
clusters of galaxies, and a determination of their content of gravitationally
bound stars, dark matter, and hot and cold gas. Using a large set of
cosmological cluster simulations, we present a detailed analysis of halo
substructures in hydrodynamical simulations of galaxy clusters, focusing in
particular on the influence both of radiative and non-radiative gas physics,
and of non-standard physics such as thermal conduction and feedback by galactic
outflows. We also examine the impact of numerical nuisance parameters such as
artificial viscosity parameterizations. We find that diffuse hot gas is
efficiently stripped from subhalos when they enter the highly pressurized
cluster atmosphere. This has the effect of decreasing the subhalo mass function
relative to a corresponding dark matter-only simulation. These effects are
mitigated in radiative runs, where baryons condense in the central subhalo
regions and form compact stellar cores. However, in all cases, only a very
small fraction, of the order of one percent, of subhalos within the cluster
virial radii preserve a gravitationally bound hot gaseous atmosphere.
(abridged)Comment: improved manuscript, to appear in MNRA
Effect of Foregrounds on the CMBR Multipole Alignment
We analyze the effect of foregrounds on the observed alignment of CMBR
quadrupole and octopole. The alignment between these multipoles is studied by
using a symmetry based approach which assigns a principal eigenvector (PEV) or
an axis with each multipole. We determine the significance of alignment between
these multipoles by using the Internal Linear Combination (ILC) 5 and 7 year
map s and also the maps obtained by using the Internal Power Spectrum
Estimation (IPSE) procedure. The effect of foreground cleaning is studied in
detail within the framework of the IPSE method both analytically and
numerically. By using simulated CMBR data, we study how the PEVs of the pure
simulated CMB map differ from those of the final cleaned map. We find that, in
general, the shift in the PEVs is relatively small and in random directions.
Due to the random nature of the shift we conclude that it can only lead to
misalignment rather than alignment of multipoles. We also directly estimate the
significance of alignment by using simulated cleaned maps. We find that the
results in this case are identical to those obtained by simple analytic
estimate or by using simulated pure CMB maps.Comment: 27 pages, 8 figure
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The Cosmic Dawn and Epoch of Reionisation with SKA
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes. Whereas IR detections have been made of sources (Lyman-α emitters, quasars and drop-outs) in this redshift regime in relatively small fields of view, no direct detection of neutral hydrogen, via the redshifted 21-cm line, has yet been established. Such a direct detection is expected in the coming years, with ongoing surveys, and could open up the entire universe from z ∼6-200 for astrophysical and cosmological studies, opening not only the Epoch of Reionization, but also its preceding Cosmic Dawn (z ∼30-15) and possibly even the later phases of the Dark Ages (z ∼200-30). All currently ongoing experiments attempt statistical detections of the 21-cm signal during the Epoch of Reionization, with limited signal-to-noise. Direct imaging, except maybe on the largest (degree) scales at lower redshifts, as well as higher redshifts will remain out of reach. The Square Kilometre Array (SKA) will revolutionize the field, allowing direct imaging of neutral hydrogen from scales of arc-minutes to degrees over most of the redshift range z ∼6-28 with SKA1-LOW, and possibly even higher redshifts with the SKA2-LOW. In this SKA will be unique, and in parallel provide enormous potential of synergy with other upcoming facilities (e.g. JWST). In this chapter we summarize the physics of 21-cm emission, the different phases the universe is thought to go through, and the observables that the SKA can probe, referring where needed to detailed chapters in this volume. This is done within the framework of the current SKA1 baseline design and a nominal CD/EoR straw-man survey, consisting of a shallow, medium-deep and deep survey, the latter probing down to ∼1 mK brightness temperature on arc-minute scales at the end of reionization. Possible minor modifications to the design of SKA1 and the upgrade to SKA2 are discussed, in addition to science that could be done already during roll-out when SKA1 still has limited capabilities and/or core collecting area
Joint Bayesian separation and restoration of CMB from convolutional mixtures
We propose a Bayesian approach to joint source separation and restoration for
astrophysical diffuse sources. We constitute a prior statistical model for the
source images by using their gradient maps. We assume a t-distribution for the
gradient maps in different directions, because it is able to fit both smooth
and sparse data. A Monte Carlo technique, called Langevin sampler, is used to
estimate the source images and all the model parameters are estimated by using
deterministic techniques.Comment: 11 pages, 6 figures. Submitted to MNRA
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