37 research outputs found
Probing Cosmic Strings with Satellite CMB measurements
We study the problem of searching for cosmic string signal patterns in the
present high resolution and high sensitivity observations of the Cosmic
Microwave Background (CMB). This article discusses a technique capable of
recognizing Kaiser-Stebbins effect signatures in total intensity anisotropy
maps, and shows that the biggest factor that produces confusion is represented
by the acoustic oscillation features of the scale comparable to the size of
horizon at recombination. Simulations show that the distribution of null
signals for pure Gaussian maps converges to a distribution, with
detectability threshold corresponding to a string induced step signal with an
amplitude of about 100 \muK which corresponds to a limit of roughly . We study the statistics of spurious detections caused by
extra-Galactic and Galactic foregrounds. For diffuse Galactic foregrounds,
which represents the dominant source of contamination, we derive sky masks
outlining the available region of the sky where the Galactic confusion is
sub-dominant, specializing our analysis to the case represented by the
frequency coverage and nominal sensitivity and resolution of the Planck
experiment.Comment: 14 pages, 3 figures, to be published in JCA
Cosmological origin of anomalous radio background
The ARCADE 2 collaboration has reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum through synchrotron emission. However, constraints from the cosmic microwave background (CMB) anisotropy, on injection of charged particles and on the primordial magnetic field, present a challenge. The simplest scenario is with a gtrsim9 GeV particle decaying into e+e− at a redshift of z ~ 5, in a magnetic field of ~ 5μG, which exceeds the CMB B-field constraints, unless the field was generated after decoupling. Decays into exotic millicharged particles can alleviate this tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field
Systematic effects in the extraction of the 'WMAP haze'
The extraction of a 'haze' from the WMAP microwave skymaps is based on
subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust
and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey
is used for the synchrotron template, the WMAP bands are at tens of GHz where
the spatial distribution of the radiating cosmic ray electrons ought to be
quite different because of the energy-dependence of their diffusion in the
Galaxy. The systematic uncertainty this introduces in the residual skymap is
comparable to the claimed haze and can, for certain source distributions, have
a very similar spectrum and latitudinal profile and even a somewhat similar
morphology. Hence caution must be exercised in interpreting the 'haze' as a
physical signature of, e.g., dark matter annihilation in the Galactic centre.Comment: 17 pages, 12 figures; improved diffusion model; extended discussion
of spectral index maps; clarifying comments, figures and references added; to
appear in JCA
Foreground removal from CMB temperature maps using an MLP neural network
One of the main obstacles in extracting the Cosmic Microwave Background (CMB)
signal from observations in the mm-submm range is the foreground contamination
by emission from galactic components: mainly synchrotron, free-free and thermal
dust emission. Due to the statistical nature of the intrinsic CMB signal it is
essential to minimize the systematic errors in the CMB temperature
determinations. Following the available knowledge of the spectral behavior of
the galactic foregrounds simple, power law-like spectra have been assumed. The
feasibility of using a simple neural network for extracting the CMB temperature
signal from the combined CMB and foreground signals has been investigated. As a
specific example, we have analysed simulated data, like that expected from the
ESA Planck Surveyor mission. A simple multilayer perceptron neural network with
2 hidden layers can provide temperature estimates, over more than 80 percent of
the sky, that are to a high degree uncorrelated with the foreground signals. A
single network will be able to cover the dynamic range of the Planck noise
level over the entire sky.Comment: Accepted for publication in Astrophysics and Space Scienc
Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument
We give a description of the design, construction and testing of the 30 and
44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the
Planck mission to be launched in 2009. The scientific requirements of the
mission determine the performance parameters to be met by the FEMs, including
their linear polarization characteristics.
The FEM design is that of a differential pseudo-correlation radiometer in
which the signal from the sky is compared with a 4-K blackbody load. The Low
Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High
Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel
phase-switch design which gives excellent amplitude and phase match across the
band.
The noise temperature requirements are met within the measurement errors at
the two frequencies. For the most sensitive LNAs, the noise temperature at the
band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively.
For some of the FEMs, the noise temperature is still falling as the ambient
temperature is reduced to 20 K. Stability tests of the FEMs, including a
measurement of the 1/f knee frequency, also meet mission requirements.
The 30 and 44 GHz FEMs have met or bettered the mission requirements in all
critical aspects. The most sensitive LNAs have reached new limits of noise
temperature for HEMTs at their band centres. The FEMs have well-defined linear
polarization characteristcs.Comment: 39 pages, 33 figures (33 EPS files), 12 tables. Planck LFI technical
papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
The GEM Project: an International Collaboration to Survey Galactic Radiation Emission
The GEM (Galactic Emission Mapping) project is an international collaboration
established with the aim of surveying the full sky at long wavelengths with a
multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz
were completed from an Equatorial site in Colombia. The observations cover the
celestial band , and . Preliminary results of this partial survey will be
discussed. A review of the instrumental setup and a
resolution sky map at 408 MHz is presented.Comment: 6 pages, Plain Latex + 1 (uuencoded) PostScript figure Fig. 1 and
Fig. 2 not included, available from [email protected]
Complementarity of Galactic radio and collider data in constraining WIMP dark matter models
In this work we confront dark matter models to constraints that may be
derived from radio synchrotron radiation from the Galaxy, taking into account
the astrophysical uncertainties and we compare these to bounds set by
accelerator and complementary indirect dark matter searches. Specifically we
apply our analysis to three popular particle physics models. First, a generic
effective operator approach, in which case we set bounds on the corresponding
mass scale, and then, two specific UV completions, the Z' and Higgs portals. We
show that for many candidates, the radio synchrotron limits are competitive
with the other searches, and could even give the strongest constraints (as of
today) with some reasonable assumptions regarding the astrophysical
uncertainties.Comment: 22 pages, 12 figure
An analysis of the FIR/RADIO Continuum Correlation in the Small Magellanic Cloud
The local correlation between far-infrared (FIR) emission and radio-continuum
(RC) emission for the Small Magellanic Cloud (SMC) is investigated over scales
from 3 kpc to 0.01 kpc. Here, we report good FIR/RC correlation down to ~15 pc.
The reciprocal slope of the FIR/RC emission correlation (RC/FIR) in the SMC is
shown to be greatest in the most active star forming regions with a power law
slope of ~1.14 indicating that the RC emission increases faster than the FIR
emission. The slope of the other regions and the SMC are much flatter and in
the range of 0.63-0.85. The slopes tend to follow the thermal fractions of the
regions which range from 0.5 to 0.95. The thermal fraction of the RC emission
alone can provide the expected FIR/RC correlation. The results are consistent
with a common source for ultraviolet (UV) photons heating dust and Cosmic Ray
electrons (CRe-s) diffusing away from the star forming regions. Since the CRe-s
appear to escape the SMC so readily, the results here may not provide support
for coupling between the local gas density and the magnetic field intensity.Comment: 19 pages, 7 Figure
First attempt at measuring the CMB cross-polarization
We compute upper limits on CMB cross-polarization by cross-correlating the
PIQUE and Saskatoon experiments. We also discuss theoretical and practical
issues relevant to measuring cross-polarization and illustrate them with
simulations of the upcoming BOOMERanG 2002 experiment. We present a method that
separates all six polarization power spectra (TT, EE, BB, TE, TB, EB) without
any other "leakage" than the familiar EE-BB mixing caused by incomplete sky
coverage. Since E and B get mixed, one might expect leakage between TE and TB,
between EE and EB and between BB and EB - our method eliminates this by
preserving the parity symmetry under which TB and EB are odd and the other four
power spectra are even.Comment: Polarization movies can be found at
http://www.hep.upenn.edu/~angelica/polarization.htm
Diffuse source separation in CMB observations
We review issues and methods for diffuse component separation in the context of Cosmic Microwave Background observation