1,661 research outputs found
CMBPol Mission Concept Study: Prospects for polarized foreground removal
In this report we discuss the impact of polarized foregrounds on a future
CMBPol satellite mission. We review our current knowledge of Galactic polarized
emission at microwave frequencies, including synchrotron and thermal dust
emission. We use existing data and our understanding of the physical behavior
of the sources of foreground emission to generate sky templates, and start to
assess how well primordial gravitational wave signals can be separated from
foreground contaminants for a CMBPol mission. At the estimated foreground
minimum of ~100 GHz, the polarized foregrounds are expected to be lower than a
primordial polarization signal with tensor-to-scalar ratio r=0.01, in a small
patch (~1%) of the sky known to have low Galactic emission. Over 75% of the sky
we expect the foreground amplitude to exceed the primordial signal by about a
factor of eight at the foreground minimum and on scales of two degrees. Only on
the largest scales does the polarized foreground amplitude exceed the
primordial signal by a larger factor of about 20. The prospects for detecting
an r=0.01 signal including degree-scale measurements appear promising, with 5
sigma_r ~0.003 forecast from multiple methods. A mission that observes a range
of scales offers better prospects from the foregrounds perspective than one
targeting only the lowest few multipoles. We begin to explore how optimizing
the composition of frequency channels in the focal plane can maximize our
ability to perform component separation, with a range of typically 40 < nu <
300 GHz preferred for ten channels. Foreground cleaning methods are already in
place to tackle a CMBPol mission data set, and further investigation of the
optimization and detectability of the primordial signal will be useful for
mission design.Comment: 42 pages, 14 figures, Foreground Removal Working Group contribution
to the CMBPol Mission Concept Study, v2, matches AIP versio
Magna Carta: History, context and influence: Papers delivered at Peking University on the 800th anniversary of Magna Carta
This book examines the history and influence of Magna Carta in British and American history. In a series of essays written by notable British specialists, it considers the origins of the document in the political and religious contexts of the thirteenth century, the relevance of its principles to the seventeenth century disputes that led to the Civil War, the uses made of Magna Carta to justify the American Revolution, and its inspiration of the radical-democratic movement in Britain in the early nineteenth century. The introductory essay considers the celebration of Magna Carta's 800th anniversary in 2015 in relation to ceremonials and remembrance in Britain in general. Given as papers to a joint conference of British and Chinese historians in Beijing in 2015, these essays provide a clear and insightful overview of the origins and impact of a medieval document that has shaped the history of the world
A new measurement of the evolving near-infrared galaxy luminosity function out to z~4: a continuing challenge to theoretical models of galaxy formation
We present the most accurate measurement to date of cosmological evolution of
the near-infrared galaxy luminosity function, from the local Universe out to
z~4. The analysis is based on a large and highly complete sample of galaxies
selected from the first data release of the UKIDSS Ultra Deep Survey.
Exploiting a master catalogue of K- and z-band selected galaxies over an area
of 0.7 square degrees, we analyse a sample of ~50,000 galaxies, all with
reliable photometry in 16-bands from the far-ultraviolet to the mid-infrared.
The unique combination of large area and depth provided by the Ultra Deep
Survey allows us to trace the evolution of the K-band luminosity function with
unprecedented accuracy. In particular, via a maximum likelihood analysis we
obtain a simple parameterization for the luminosity function and its
cosmological evolution, including both luminosity and density evolution, which
provides an excellent description of the data from z =0 up to z~4. We find
differential evolution for galaxies dependent on galaxy luminosity, revealing
once again the ``down-sizing behaviour'' of galaxy formation. Finally, we
compare our results with the predictions of the latest theoretical models of
galaxy formation, based both on semi-analytical prescriptions, and on full
hydrodynamical simulations.Comment: 11 pages, 6 figures, submitted to MNRA
Inhibition of microbial biofuel production in drought-stressed switchgrass hydrolysate
Additional file 2. Maps of significant gene ontology terms for chemical genomics data. Untreated biomass composition. Detailed hydrolysate composition
First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475
The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and
95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to
measure the anisotropy in the polarization of the CMB. QUIET primarily targets
the B modes from primordial gravitational waves. The combination of these
frequencies gives sensitivity to foreground contributions from diffuse Galactic
synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of
data were collected, first with the 19-element 43GHz array (3458hours) and then
with the 90-element 95GHz array. Each array observes the same four fields,
selected for low foregrounds, together covering ~1000deg^2. This paper reports
initial results from the 43GHz receiver which has an array sensitivity to CMB
fluctuations of 69uK sqrt(s). The data were extensively studied with a large
suite of null tests before the power spectra, determined with two independent
pipelines, were examined. Analysis choices, including data selection, were
modified until the null tests passed. Cross correlating maps with different
telescope pointings is used to eliminate a bias. This paper reports the EE, BB
and EB power spectra in the multipole range ell=25-475. With the exception of
the lowest multipole bin for one of the fields, where a polarized foreground,
consistent with Galactic synchrotron radiation, is detected with 3sigma
significance, the E-mode spectrum is consistent with the LCDM model, confirming
the only previous detection of the first acoustic peak. The B-mode spectrum is
consistent with zero, leading to a measurement of the tensor-to-scalar ratio of
r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation
technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent
boresight rotation leads to the lowest level of systematic contamination in the
B-mode power so far reported, below the level of r=0.1Comment: 19 pages, 14 figures, higher quality figures are available at
http://quiet.uchicago.edu/results/index.html; Fixed a typo and corrected
statistical error values used as a reference in Figure 14, showing our
systematic uncertainties (unchanged) vs. multipole; Revision to ApJ accepted
version, this paper should be cited as "QUIET Collaboration et al. (2011)
High sensitivity measurements of the CMB power spectrum with the extended Very Small Array
We present deep Ka-band ( GHz) observations of the CMB made
with the extended Very Small Array (VSA). This configuration produces a
naturally weighted synthesized FWHM beamwidth of arcmin which covers
an -range of 300 to 1500. On these scales, foreground extragalactic
sources can be a major source of contamination to the CMB anisotropy. This
problem has been alleviated by identifying sources at 15 GHz with the Ryle
Telescope and then monitoring these sources at 33 GHz using a single baseline
interferometer co-located with the VSA. Sources with flux densities \gtsim 20
mJy at 33 GHz are subtracted from the data. In addition, we calculate a
statistical correction for the small residual contribution from weaker sources
that are below the detection limit of the survey.
The CMB power spectrum corrected for Galactic foregrounds and extragalactic
point sources is presented. A total -range of 150-1500 is achieved by
combining the complete extended array data with earlier VSA data in a compact
configuration. Our resolution of allows the first 3
acoustic peaks to be clearly delineated. The is achieved by using mosaiced
observations in 7 regions covering a total area of 82 sq. degrees. There is
good agreement with WMAP data up to where WMAP data run out of
resolution. For higher -values out to , the agreement in
power spectrum amplitudes with other experiments is also very good despite
differences in frequency and observing technique.Comment: 16 pages. Accepted in MNRAS (minor revisions
The QUIET Instrument
The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the
Cosmic Microwave Background, targeting the imprint of inflationary
gravitational waves at large angular scales (~ 1 degree). Between 2008 October
and 2010 December, two independent receiver arrays were deployed sequentially
on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal
planes use a highly compact design based on High Electron Mobility Transistors
(HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U,
and I in a single module. The 17-element Q-band polarimeter array, with a
central frequency of 43.1 GHz, has the best sensitivity (69 uK sqrt(s)) and the
lowest instrumental systematic errors ever achieved in this band, contributing
to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter
array has a sensitivity of 87 uK sqrt(s) at a central frequency of 94.5 GHz. It
has the lowest systematic errors to date, contributing at r < 0.01. The two
arrays together cover multipoles in the range l= 25-975. These are the largest
HEMT-based arrays deployed to date. This article describes the design,
calibration, performance of, and sources of systematic error for the
instrument
Recommended from our members
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Planck Intermediate Results. IX. Detection of the Galactic haze with Planck
Using precise full-sky observations from Planck, and applying several methods
of component separation, we identify and characterize the emission from the
Galactic "haze" at microwave wavelengths. The haze is a distinct component of
diffuse Galactic emission, roughly centered on the Galactic centre, and extends
to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining
the Planck data with observations from the WMAP we are able to determine the
spectrum of this emission to high accuracy, unhindered by the large systematic
biases present in previous analyses. The derived spectrum is consistent with
power-law emission with a spectral index of -2.55 +/- 0.05, thus excluding
free-free emission as the source and instead favouring hard-spectrum
synchrotron radiation from an electron population with a spectrum (number
density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the
microwave haze morphology is consistent with that of the Fermi gamma-ray "haze"
or "bubbles," indicating that we have a multi-wavelength view of a distinct
component of our Galaxy. Given both the very hard spectrum and the extended
nature of the emission, it is highly unlikely that the haze electrons result
from supernova shocks in the Galactic disk. Instead, a new mechanism for
cosmic-ray acceleration in the centre of our Galaxy is implied.Comment: 15 pages, 9 figures, submitted to Astronomy and Astrophysic
Extragalactic Background Light Inferred from AEGIS Galaxy SED-type Fractions
The extragalactic background light (EBL) is of fundamental importance both
for understanding the entire process of galaxy evolution and for gamma-ray
astronomy, but the overall spectrum of the EBL between 0.1-1000 microns has
never been determined directly from galaxy spectral energy distribution (SED)
observations over a wide redshift range. The evolving, overall spectrum of the
EBL is derived here utilizing a novel method based on observations only. This
is achieved from the observed evolution of the rest-frame K-band galaxy
luminosity function up to redshift 4 (Cirasuolo et al. 2010), combined with a
determination of galaxy SED-type fractions. These are based on fitting SWIRE
templates to a multiwavelength sample of about 6000 galaxies in the redshift
range from 0.2 to 1 from the All-wavelength Extended Groth Strip International
Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming
galaxies, starburst galaxies and AGN galaxies in that redshift range are
estimated, and two alternative extrapolations of SED-types to higher redshifts
are considered. This allows calculation of the evolution of the luminosity
densities from the UV to the IR, the evolving star formation rate density of
the universe, the evolving contribution to the bolometric EBL from the
different galaxy populations including AGN galaxies and the buildup of the EBL.
Our EBL calculations are compared with those from a semi-analytic model, from
another observationally-based model and observational data. The EBL
uncertainties in our modeling based directly on the data are quantified, and
their consequences for attenuation of very high energy gamma-rays due to pair
production on the EBL are discussed. It is concluded that the EBL is well
constrained from the UV to the mid-IR, but independent efforts from infrared
and gamma-ray astronomy are needed in order to reduce the uncertainties in the
far-IR.Comment: 25 pages, 18 figures, 4 tables; accepted for publication in MNRAS on
September 3, 2010. Online material available at http://side.iaa.es/EB
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