120 research outputs found
The C-Band All-Sky Survey (C-BASS): Constraining diffuse Galactic radio emission in the North Celestial Pole region
The C-Band All-Sky Survey C-BASS is a high-sensitivity all-sky radio survey
at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a
total intensity 4.7 GHz map of the North Celestial Pole (NCP) region of sky,
above declination +80 deg, which is limited by source confusion at a level of
~0.6 mK rms. We apply the template-fitting (cross-correlation) technique to
WMAP and Planck data, using the C-BASS map as the synchrotron template, to
investigate the contribution of diffuse foreground emission at frequencies
~20-40 GHz. We quantify the anomalous microwave emission (AME) that is
correlated with far-infrared dust emission. The AME amplitude does not change
significantly (<10%) when using the higher frequency C-BASS 4.7 GHz template
instead of the traditional Haslam 408 MHz map as a tracer of synchrotron
radiation. We measure template coefficients of and
K per unit when using the Haslam and C-BASS synchrotron templates,
respectively. The AME contributes K rms at 22.8 GHz and accounts
for ~60% of the total foreground emission. Our results suggest that a harder
(flatter spectrum) component of synchrotron emission is not dominant at
frequencies >5 GHz; the best-fitting synchrotron temperature spectral index is
from 4.7 to 22.8 GHz and from 22.8 to
44.1 GHz. Free-free emission is weak, contributing ~K rms (~7%) at 22.8
GHz. The best explanation for the AME is still electric dipole emission from
small spinning dust grains.Comment: 18 pages, 6 figures, version matches version accepted by MNRA
Detection of Spectral Variations of Anomalous Microwave Emission with QUIJOTE and C-BASS
Anomalous Microwave Emission (AME) is a significant component of Galactic
diffuse emission in the frequency range -GHz and a new window into
the properties of sub-nanometre-sized grains in the interstellar medium. We
investigate the morphology of AME in the diameter
Orionis ring by combining intensity data from the QUIJOTE experiment at ,
, and GHz and the C-Band All Sky Survey (C-BASS) at GHz,
together with 19 ancillary datasets between and GHz. Maps of
physical parameters at resolution are produced through Markov Chain
Monte Carlo (MCMC) fits of spectral energy distributions (SEDs), approximating
the AME component with a log-normal distribution. AME is detected in excess of
at degree-scales around the entirety of the ring along
photodissociation regions (PDRs), with three primary bright regions containing
dark clouds. A radial decrease is observed in the AME peak frequency from
GHz near the free-free region to GHz in the outer
regions of the ring, which is the first detection of AME spectral variations
across a single region. A strong correlation between AME peak frequency,
emission measure and dust temperature is an indication for the dependence of
the AME peak frequency on the local radiation field. The AME amplitude
normalised by the optical depth is also strongly correlated with the radiation
field, giving an overall picture consistent with spinning dust where the local
radiation field plays a key role.Comment: 19 pages, 7 figures, accepted for publication by MNRA
C-Band All-Sky Survey (C-BASS): Simulated parametric fitting in single pixels in total intensity and polarization
The cosmic microwave background (CMB) B-mode signal is potentially weaker than the diffuse Galactic foregrounds over most of the sky at any frequency. A common method of separating the CMB from these foregrounds is via pixel-based parametric-model fitting. There are not currently enough all-sky maps to fit anything more than the most simple models of the sky. By simulating the emission in seven representative pixels, we demonstrate that the inclusion of a 5 GHz data point allows for more complex models of low-frequency foregrounds to be fitted than at present. It is shown that the inclusion of the C-BASS data will significantly reduce the uncertainties in a number of key parameters in the modelling of both the galactic foregrounds and the CMB. The extra data allow estimates of the synchrotron spectral index to be constrained much more strongly than is presently possible, with corresponding improvements in the accuracy of the recovery of the CMB amplitude. However, we show that to place good limits on models of the synchrotron spectral curvature will require additional low-frequency data
The C-Band All-Sky Survey (C-BASS): Simulated parametric fitting in single pixels in total intensity and polarization
The cosmic microwave background (CMB) B-mode signal is potentially weaker than the diffuse Galactic foregrounds over most of the sky at any frequency. A common method of separating the CMB from these foregrounds is via pixel-based parametric-model fitting. There are not currently enough all-sky maps to fit anything more than the most simple models of the sky. By simulating the emission in seven representative pixels, we demonstrate that the inclusion of a 5 GHz data point allows for more complex models of low-frequency foregrounds to be fitted than at present. It is shown that the inclusion of the C-BASS data will significantly reduce the uncertainties in a number of key parameters in the modelling of both the galactic foregrounds and the CMB. The extra data allow estimates of the synchrotron spectral index to be constrained much more strongly than is presently possible, with corresponding improvements in the accuracy of the recovery of the CMB amplitude. However, we show that to place good limits on models of the synchrotron spectral curvature will require additional low-frequency data
The State-of-Play of Anomalous Microwave Emission (AME) Research
Anomalous Microwave Emission (AME) is a component of diffuse Galactic
radiation observed at frequencies in the range -60 GHz. AME was
first detected in 1996 and recognised as an additional component of emission in
1997. Since then, AME has been observed by a range of experiments and in a
variety of environments. AME is spatially correlated with far-IR thermal dust
emission but cannot be explained by synchrotron or free-free emission
mechanisms, and is far in excess of the emission contributed by thermal dust
emission with the power-law opacity consistent with the observed emission at
sub-mm wavelengths. Polarization observations have shown that AME is very
weakly polarized (%). The most natural explanation for AME is
rotational emission from ultra-small dust grains ("spinning dust"), first
postulated in 1957. Magnetic dipole radiation from thermal fluctuations in the
magnetization of magnetic grain materials may also be contributing to the AME,
particularly at higher frequencies ( GHz). AME is also an important
foreground for Cosmic Microwave Background analyses. This paper presents a
review and the current state-of-play in AME research, which was discussed in an
AME workshop held at ESTEC, The Netherlands, June 2016.Comment: Accepted for publication in New Astronomy Reviews. Summary of AME
workshop held at ESTEC, The Netherlands, June 2016, 40 pages, 18 figures.
Updated to approximately match published versio
The C-Band All-Sky Survey (C-BASS): constraining diffuse Galactic radio emission in the North Celestial Pole region
The C-Band All-Sky Survey (C-BASS) is a high sensitivity all-sky radio survey at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a total intensity map of the North Celestial Pole (NCP) region of sky, above declination >+80°, which is limited by source confusion at a level of ≈0.6 mK rms. We apply the template-fitting (cross-correlation) technique to WMAP and Planck data, using the C-BASS map as the synchrotron template, to investigate the contribution of diffuse foreground emission at frequencies ∼20–40 GHz. We quantify the anomalous microwave emission (AME) that is correlated with far-infrared dust emission. The AME amplitude does not change significantly (<10 per cent) when using the higher frequency C-BASS 4.7 GHz template instead of the traditional Haslam 408 MHz map as a tracer of synchrotron radiation. We measure template coefficients of 9.93 ± 0.35 and 9.52 ± 0.34 K per unit τ_(353) when using the Haslam and C-BASS synchrotron templates, respectively. The AME contributes 55 ± 2μK rms at 22.8 GHz and accounts for ≈60 per cent of the total foreground emission. Our results show that a harder (flatter spectrum) component of synchrotron emission is not dominant at frequencies ≳5 GHz; the best-fitting synchrotron temperature spectral index is β = −2.91 ± 0.04 from 4.7 to 22.8 GHz and β = −2.85 ± 0.14 from 22.8 to 44.1 GHz. Free–free emission is weak, contributing ≈7μK rms (≈7 per cent) at 22.8 GHz. The best explanation for the AME is still electric dipole emission from small spinning dust grains
The C-Band All-Sky Survey: total intensity point-source detection over the northern sky
We present a point-source detection algorithm that employs the second-order Spherical Mexican Hat wavelet filter (SMHW2), and use it on C-Band All-Sky Survey (C-BASS) northern intensity data to produce a catalogue of point sources. This catalogue allows us to cross-check the C-BASS flux-density scale against existing source surveys, and provides the basis for a source mask that will be used in subsequent C-BASS and cosmic microwave background (CMB) analyses. The SMHW2 allows us to filter the entire sky at once, avoiding complications from edge effects arising when filtering small sky patches. The algorithm is validated against a set of Monte Carlo simulations, consisting of diffuse emission, instrumental noise, and various point-source populations. The simulated source populations are successfully recovered. The SMHW2 detection algorithm is used to produce a 4.76GHz northern sky source catalogue in total intensity, containing 1784 sources and covering declinations δ ≥ −10°. The C-BASS catalogue is matched with the Green Bank 6 cm (GB6) and Parkes-MIT-NRAO (PMN) catalogues over their areas of common sky coverage. From this we estimate the 90 per cent completeness level to be approximately 610mJy, with a corresponding reliability of 98 per cent, when masking the brightest 30 per cent of the diffuse emission in the C-BASS northern sky map. We find the C-BASS and GB6 flux-density scales to be consistent with one another to within approximately 4 per cent
Biofunctional activity of tortillas and bars enhanced with nopal. Preliminary assessment of functional effect after intake on the oxidative status in healthy volunteers
- …