1,478 research outputs found
A 3D model for carbon monoxide molecular line emission as a potential cosmic microwave background polarization contaminant
We present a model for simulating Carbon Monoxide (CO) rotational line emission in molecular clouds, taking account of their 3D spatial distribution in galaxies with different geometrical properties. The model implemented is based on recent results in the literature and has been designed for performing Monte-Carlo simulations of this emission. We compare the simulations produced with this model and calibrate them, both on the map level and on the power spectrum level, using the second release of data from the Planck satellite for the Galactic plane, where the signal-to-noise ratio is highest. We use the calibrated model to extrapolate the CO power spectrum at low Galactic latitudes where no high sensitivity observations are available yet. We then forecast the level of unresolved polarized emission from CO molecular clouds which could contaminate the power spectrum of Cosmic Microwave Background (CMB) polarization B-modes away from the Galactic plane. Assuming realistic levels of the polarization fraction, we show that the level of contamination is equivalent to a cosmological signal with r 720.02. The Monte-Carlo MOlecular Line Emission (MCMole3D) Python package, which implements this model, is being made publicly available
Bubble size statistics during reionization from 21-cm tomography
The upcoming SKA1-Low radio interferometer will be sensitive enough to produce tomographic imaging data of the redshifted 21-cm signal from the Epoch of Reionization. Due to the non-Gaussian distribution of the signal, a power spectrum analysis alone will not provide a complete description of its properties. Here, we consider an additional metric which could be derived from tomographic imaging data, namely the bubble size distribution of ionized regions. We study three methods that have previously been used to characterize bubble size distributions in simulation data for the hydrogen ionization fraction â the spherical-average (SPA), mean-free-path (MFP) and friends-of-friends (FOF) methods â and apply them to simulated 21-cm data cubes. Our simulated data cubes have the (sensitivity-dictated) resolution expected for the SKA1-Low reionization experiment and we study the impact of both the light-cone (LC) and redshift space distortion (RSD) effects. To identify ionized regions in the 21-cm data we introduce a new, self-adjusting thresholding approach based on the K-Means algorithm. We find that the fraction of ionized cells identified in this way consistently falls below the mean volume-averaged ionized fraction. From a comparison of the three bubble size methods, we conclude that all three methods are useful, but that the MFP method performs best in terms of tracking the progress of reionization and separating different reionization scenarios. The LC effect is found to affect data spanning more than about 10 MHz in frequency (Îz ⌠0.5). We find that RSDs only marginally affect the bubble size distributions
Low-resolution spectroscopy of the Sunyaev-Zel'dovich effect and estimates of cluster parameters
The Sunyaev-Zel'dovich (SZ) effect is a powerful tool for studying clusters
of galaxies and cosmology. Large mm-wave telescopes are now routinely detecting
and mapping the SZ effect in a number of clusters, measure their comptonisation
parameter and use them as probes of the large-scale structure and evolution of
the universe. We show that estimates of the physical parameters of clusters
(optical depth, plasma temperature, peculiar velocity, non-thermal components
etc.) obtained from ground-based multi-band SZ photometry can be significantly
biased, owing to the reduced frequency coverage, to the degeneracy between the
parameters and to the presence of a number of independent components larger
than the number of frequencies measured. We demonstrate that low-resolution
spectroscopic measurements of the SZ effect that also cover frequencies
GHz are effective in removing the degeneracy. We used accurate simulations of
observations with lines-of-sight through clusters of galaxies with different
experimental configurations (4-band photometers, 6-band photometer, multi-range
differential spectrometer, full coverage spectrometers) and different
intracluster plasma stratifications. We find that measurements carried out with
ground-based few-band photometers are biased towards high electron temperatures
and low optical depths, and require coverage of high frequency and/or
independent complementary observations to produce unbiased information; a
differential spectrometer that covers 4 bands with a resolution of $\sim 6 \
GHz$ eliminates most if not all bias; full-range differential spectrometers are
the ultimate resource that allows a full recovery of all parameters.Comment: in pres
Cosmological CPT Violation and CMB Polarization Measurements
In this paper we study the possibility of testing Charge-Parity-Time Reversal
(CPT) symmetry with cosmic microwave background (CMB) experiments. We consider
two kinds of Chern-Simons (CS) term, electromagnetic CS term and gravitational
CS term, and study their effects on the CMB polarization power spectra in
detail. By combining current CMB polarization measurements, the seven-year
WMAP, BOOMERanG 2003 and BICEP observations, we obtain a tight constraint on
the rotation angle deg (), indicating a
detection of the CPT violation. Here, we particularly take the
systematic errors of CMB measurements into account. After adding the QUaD
polarization data, the constraint becomes deg at 95%
confidence level. When comparing with the effect of electromagnetic CS term,
the gravitational CS term could only generate TB and EB power spectra with much
smaller amplitude. Therefore, the induced parameter can not be
constrained from the current polarization data. Furthermore, we study the
capabilities of future CMB measurements, Planck and CMBPol, on the constraints
of and . We find that the constraint of
can be significantly improved by a factor of 15. Therefore, if this rotation
angle effect can not be taken into account properly, the constraints of
cosmological parameters will be biased obviously. For the gravitational CS
term, the future Planck data still can not constrain very well, if
the primordial tensor perturbations are small, . We need the more
accurate CMBPol experiment to give better constraint on .Comment: 11 pages, 5 figures, 4 tables, Accepted for publication in JCA
Constraining the time variation of the coupling constants from cosmic microwave background: effect of \Lambda_{QCD}
We investigate constraints on the time variation of the fine structure
constant between the recombination epoch and the present epoch,
\Delta\alpha/\alpha \equiv (\alpha_{rec} - \alpha_{now})/\alpha_{now}, from
cosmic microwave background (CMB) taking into account simultaneous variation of
other physical constants, namely the electron mass m_{e} and the proton mass
m_{p}. In other words, we consider the variation of Yukawa coupling and the QCD
scale \Lambda_{QCD} in addition to the electromagnetic coupling. We clarify
which parameters can be determined from CMB temperature anisotropy in terms of
singular value decomposition. Assuming a relation among variations of coupling
constants governed by a single scalar field (the dilaton), the 95% confidence
level (C.L.) constraint on \Delta\alpha/\alpha is found to be -8.28 \times
10^{-3} < \Delta\alpha/\alpha < 1.81 \times 10^{-3}, which is tighter than the
one obtained by considering only the change of \alpha and m_{e}. We also obtain
the constraint on the time variation of the proton-to-electron mass ratio \mu
\equiv m_{p}/m_{e} to be -0.52 < \Delta\mu/\mu < 0.17 (95% C.L.) under the same
assumption. Finally, we also implement a forecast for constraints from the
PLANCK survey.Comment: 25 pages, 4 figures; references adde
On the statistics of proto-cluster candidates detected in the Planck all-sky survey
Observational investigations of the abundance of massive precursors of local
galaxy clusters ("proto-clusters") allow us to test the growth of density
perturbations, to constrain cosmological parameters that control it, to test
the theory of non-linear collapse and how the galaxy formation takes place in
dense environments. The Planck collaboration has recently published a catalogue
of >~ 2000 cold extra-galactic sub-millimeter sources, i.e. with colours
indicative of z >~ 2, almost all of which appear to be over-densities of
star-forming galaxies. They are thus considered as proto-cluster candidates.
Their number densities (or their flux densities) are far in excess of
expectations from the standard scenario for the evolution of large-scale
structure. Simulations based on a physically motivated galaxy evolution model
show that essentially all cold peaks brighter than S_545GHz = 500 mJy found
in Planck maps after having removed the Galactic dust emission can be
interpreted as positive Poisson fluctuations of the number of high-z dusty
proto-clusters within the same Planck beam, rather then being individual clumps
of physically bound galaxies. This conclusion does not change if an empirical
fit to the luminosity function of dusty galaxies is used instead of the
physical model. The simulations accurately reproduce the statistic of the
Planck detections and yield distributions of sizes and ellipticities in
qualitative agreement with observations. The redshift distribution of the
brightest proto-clusters contributing to the cold peaks has a broad maximum at
1.5 <~ z <~ 3. Therefore follow-up of Planck proto-cluster candidates will
provide key information on the high-z evolution of large scale structure
Galactic interstellar filaments as probed by LOFAR and Planck
Recent Low Frequency Array (LOFAR) observations at 115-175 MHz of a field at
medium Galactic latitudes (centered at the bright quasar 3C196) have shown
striking filamentary structures in polarization that extend over more than 4
degrees across the sky. In addition, the Planck satellite has released full sky
maps of the dust emission in polarization at 353GHz. The LOFAR data resolve
Faraday structures along the line of sight, whereas the Planck dust
polarization maps probe the orientation of the sky projected magnetic field
component. Hence, no apparent correlation between the two is expected. Here we
report a surprising, yet clear, correlation between the filamentary structures,
detected with LOFAR, and the magnetic field orientation, probed by the Planck
satellite. This finding points to a common, yet unclear, physical origin of the
two measurements in this specific area in the sky. A number of follow-up multi-
frequency studies are proposed to shed light on this unexpected finding.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
Radio to infrared spectra of late-type galaxies with Planck and WMAP data
We use the Planck Early Release Compact Source Catalogue combined with WMAP
and other archival measurements to construct continuum spectra of three nearby
dusty star-forming galaxies: Messier 82, NGC 253 and NGC 4945. We carry out a
least-squares fit to the spectra using a combination of simple synchrotron,
free-free and thermal dust models, and look for evidence of anomalous microwave
emission (AME). We find that the radio spectra of all three galaxies are
consistent with steep spectrum synchrotron emission, with a significant amount
of free-free emission required to explain the Planck and WMAP data points in
the frequency range 30-150 GHz. This brings the star-formation rate based on
free-free emission into better agreement with that from the non-thermal
emission. We place limits on the presence of AME in these galaxies, finding
that it is lower than expectations based on the ratio of far infrared to AME
from the Galaxy. Nevertheless, the shape of the spectrum of NGC 4945 hints at
the presence of AME with a peak around 30 GHz. Future Planck data will let us
look more closely at these galaxies, as well as to extend the analysis to many
more galaxies.Comment: 5 pages, 1 figure (6 panels), 1 table. Submitted to MNRAS letter
Isocurvature forecast in the anthropic axion window
We explore the cosmological sensitivity to the amplitude of isocurvature
fluctuations that would be caused by axions in the "anthropic window" where the
axion decay constant f_a >> 10^12 GeV and the initial misalignment angle
Theta_i << 1. In a minimal Lambda-CDM cosmology extended with subdominant
scale-invariant isocurvature fluctuations, existing data constrain the
isocurvature fraction to alpha < 0.09 at 95% C.L. If no signal shows up, Planck
can improve this constraint to 0.042 while an ultimate CMB probe limited only
by cosmic variance in both temperature and E-polarisation can reach 0.017,
about a factor of five better than the current limit. In the parameter space of
f_a and H_I (Hubble parameter during inflation) we identify a small region
where axion detection remains within the reach of realistic cosmological
probes.Comment: 14 pages, 4 figures; v2: matches published versio
Optimising Boltzmann codes for the Planck era
High precision measurements of the Cosmic Microwave Background (CMB)
anisotropies, as can be expected from the Planck satellite, will require
high-accuracy theoretical predictions as well. One possible source of
theoretical uncertainty is the numerical error in the output of the Boltzmann
codes used to calculate angular power spectra. In this work, we carry out an
extensive study of the numerical accuracy of the public Boltzmann code CAMB,
and identify a set of parameters which determine the error of its output. We
show that at the current default settings, the cosmological parameters
extracted from data of future experiments like Planck can be biased by several
tenths of a standard deviation for the six parameters of the standard
Lambda-CDM model, and potentially more seriously for extended models. We
perform an optimisation procedure that leads the code to achieve sufficient
precision while at the same time keeping the computation time within reasonable
limits. Our conclusion is that the contribution of numerical errors to the
theoretical uncertainty of model predictions is well under control -- the main
challenges for more accurate calculations of CMB spectra will be of an
astrophysical nature instead.Comment: 13 pages, 4 figure
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