168 research outputs found
Observations of Anomalous Microwave Emission from HII regions
In this brief review, I give a summary of the observations of Anomalous
Microwave Emission (AME) from HII regions. AME has been detected in, or in the
vicinity of, HII regions. Given the difficulties in measuring accurate SEDs
over a wide range of frequencies and in complex environments, many of these
detections require more data to confirm them as emitting significant AME. The
contribution from optically thick free-free emission from UCHII regions may be
also be significant in some cases. The AME emissivity, defined as the ratio of
the AME brightness to the 100 micron brightness, is comparable to the value
observed in high-latitude diffuse cirrus in some regions, but is significantly
lower in others. However, this value is dependent on the dust temperature. More
data, both at high frequencies (>5 GHz) and high resolution (~1 arcmin or
better) is required to disentangle the emission processes in such complex
regions.Comment: Published in Advances in Astronomy. Final manuscript can be
downloaded from http://www.hindawi.com/journals/aa/2013/162478
CMB foregrounds - A brief review
CMB foregrounds consist of all radiation between the surface of last
scattering and the detectors, which can interfere with the cosmological
interpretation of CMB data. Fortunately, in temperature (intensity), even
though the foregrounds are complex they can relatively easily be mitigated.
However, in polarization, diffuse Galactic radiation (synchrotron and thermal
dust) can be polarized at a level of >10 % making it more of a challenge. In
particular, CMB B-modes, which are a smoking-gun signature of inflation, will
be dominated by foregrounds. Component separation will therefore be critical
for future CMB polarization missions, requiring many channels covering a wide
range of frequencies, to ensure that foreground modelling errors are minimised.Comment: Draft proceedings for the conference Rencontres de Moriond 2016 on
cosmology. Invited review talk, 9 pages, 6 figure
CMB interferometry
Interferometry has been a very successful tool for measuring anisotropies in
the cosmic microwave background. Interferometers provided the first constraints
on CMB anisotropies on small angular scales (l~10000) in the 1980s and then in
the late 1990s and early 2000s made ground-breaking measurements of the CMB
power spectrum at intermediate and small angular scales covering the l-range
~100-4000. In 2002 the DASI made the first detection of CMB polarization which
remains a major goal for current and future CMB experiments. Interferometers
have also made major contributions to the detection and surveying of the
Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. In this short review I cover
the key aspects that made interferometry well-suited to CMB measurements and
summarise some of the central observations that have been made. I look to the
future and in particular to HI intensity mapping at high redshifts that could
make use of the advantages of interferometry.Comment: 8 pages, 2 tables. Accepted in Proceedings of Science (PoS) as part
of conference: Resolving the Sky - Radio Interferometry: Past, Present
andFuture - RTS2012, April 17-20, 2012, Manchester, U
Potential Impact of Global Navigation Satellite Services on Total Power HI Intensity Mapping Surveys
Future total-power single-dish HI intensity mapping (HI IM) surveys have the
potential to provide unprecedented insight into late time () cosmology
that are competitive with Stage IV dark energy surveys. However, redshifts
between lie within the transmission bands of global navigation
satellite services (GNSS), and even at higher redshifts out-of-band leakage
from GNSS satellites may be problematic. We estimate the impact of GNSS
satellites on future single-dish HI IM surveys using realistic estimates of
both the total power and spectral structure of GNSS signals convolved with a
model SKA beam. Using a simulated SKA HI IM survey covering 30000 sq. deg. of
sky and 200 dishes, we compare the integrated GNSS emission on the sky with the
expected HI signal. It is found that for frequencies MHz the emission
from GNSS satellites will exceed the expected HI signal for all angular scales
to which the SKA is sensitive when operating in single-dish mode.Comment: 13 pages, 11 figures, "matches published version
Modelling the spinning dust emission from LDN 1780
We study the anomalous microwave emission (AME) in the Lynds Dark Nebula
(LDN) 1780 on two angular scales. Using available ancillary data at an angular
resolution of 1 degree, we construct an SED between 0.408 GHz to 2997 GHz. We
show that there is a significant amount of AME at these angular scales and the
excess is compatible with a physical spinning dust model. We find that LDN 1780
is one of the clearest examples of AME on 1 degree scales. We detected AME with
a significance > 20. We also find at these angular scales that the
location of the peak of the emission at frequencies between 23-70 GHz differs
from the one on the 90-3000 GHz map. In order to investigate the origin of the
AME in this cloud, we use data obtained with the Combined Array for Research in
Millimeter-wave Astronomy (CARMA) that provides 2 arcmin resolution at 30 GHz.
We study the connection between the radio and IR emissions using morphological
correlations. The best correlation is found to be with MIPS 70m, which
traces warm dust (T50K). Finally, we study the difference in radio
emissivity between two locations within the cloud. We measured a factor
of difference in 30 GHz emissivity. We show that this variation can
be explained, using the spinning dust model, by a variation on the dust grain
size distribution across the cloud, particularly changing the carbon fraction
and hence the amount of PAHs.Comment: 14 pages, 11 figures, submitted to MNRA
Constraining the Anomalous Microwave Emission Mechanism in the S140 Star Forming Region with Spectroscopic Observations Between 4 and 8 GHz at the Green Bank Telescope
Anomalous microwave emission (AME) is a category of Galactic signals that
cannot be explained by synchrotron radiation, thermal dust emission, or
optically thin free-free radiation. Spinning dust is one variety of AME that
could be partially polarized and therefore relevant for ongoing and future
cosmic microwave background polarization studies. The Planck satellite mission
identified candidate AME regions in approximately patches that were
found to have spectra generally consistent with spinning dust grain models. The
spectra for one of these regions, G107.2+5.2, was also consistent with
optically thick free-free emission because of a lack of measurements between 2
and 20 GHz. Follow-up observations were needed. Therefore, we used the C-band
receiver (4 to 8 GHz) and the VEGAS spectrometer at the Green Bank Telescope to
constrain the AME mechanism. For the study described in this paper, we produced
three band averaged maps at 4.575, 5.625, and 6.125 GHz and used aperture
photometry to measure the spectral flux density in the region relative to the
background. We found if the spinning dust description is correct, then the
spinning dust signal peaks at GHz, and it explains the excess
emission. The morphology and spectrum together suggest the spinning dust grains
are concentrated near S140, which is a star forming region inside our chosen
photometry aperture. If the AME is sourced by optically thick free-free
radiation, then the region would have to contain HII with an emission measure
of and a physical extent of
. This result suggests the HII
would have to be ultra or hyper compact to remain an AME candidate.Comment: 21 pages, 14 figures. Submitted to Ap
Anomalous Microwave Emission: Theory, Modeling, and Observations
Anomalous Microwave Emission (AME) was first identified
in the late 1990s, through sensitive high frequency radio CMB
observations. The usual emission mechanisms (e.g., blackbody,
synchrotron, and free-free) did not appear to be able
to account for the excess emission in the frequency range 10–
60GHz. Since then, a large body of observational evidence
has emerged showing that AME appears to be emitted both
in the diffuse interstellar medium at large, and from specific
clouds within our galaxy. Detections from star-forming
regions in an external galaxy have also been made. Nevertheless,
detailed measurements have been difficult due to the frequency
range (difficult to observe from the ground) and confusion
with other emission mechanisms that emit in this frequent
range. The most promising candidate for the AME
is electric dipole radiation from small spinning dust grains
(spinning dust emission). This was first predicted in the
late 50s, with major developments in the theory over the
last 15 years. The theory predicts a peaked spectrum which
emits at frequencies from about 10GHz to over 100GHz,
but with a wide range of peak frequencies and emissivities,
which depend on the local environment and dust grain size
distribution. There is still significant debate about the true
nature of the AME, and both observations and theory are still
relatively unexplored. An exciting possibility is to use detailed
radio observations of spinning dust to study the interstellar
medium, in a complementary way to the optical, UV, and
infrared domains. This special issue is dedicated to the study
of AME
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