53 research outputs found
Statistics of the fractional polarisation of compact radio sources in Planck maps
In this work we apply the stacking technique to estimate the average
fractional polarisation from 30 to 353 GHz of a primary sample of 1560 compact
sources - essentially all radio sources - detected in the 30 GHz Planck all-sky
map and listed in the second version of the Planck Catalogue of Compact Sources
(PCCS2). We divide our primary sample in two subsamples according to whether
the sources lay (679 sources) or not (881 sources) inside the sky region
defined by the Planck Galactic mask (fsky ~ 60 per cent) and the area around
the Magellanic Clouds. We find that the average fractional polarisation of
compact sources is approximately constant (with frequency) in both samples
(with a weighted mean over all the channels of 3.08 per cent outside and 3.54
per cent inside the Planck mask). In the sky region outside the adopted mask,
we also estimate the {\mu} and {\sigma} parameters for the log-normal
distribution of the fractional polarisation, finding a weighted mean value over
all the Planck frequency range of 1.0 for {\sigma} and 0.7 for {\mu} (that
would imply a weighted mean value for the median fractional polarisation of 1.9
per cent).Comment: 12 pages, 7 figures, 2 tables, MNRAS in pres
The Planck-ATCA Co-eval Observations (PACO) project: the bright sample
The Planck-ATCA Co-eval Observations (PACO) have provided flux density
measurements of well defined samples of AT20G radio sources at frequencies
below and overlapping with Planck frequency bands, almost simultaneously with
Planck observations. We have observed with the Australia Telescope Compact
Array (ATCA) a total of 482 sources in the frequency range between 4.5 and 40
GHz in the period between July 2009 and August 2010. Several sources were
observed more than once. In this paper we present the aims of the project, the
selection criteria, and the observation and data reduction procedures. We also
discuss the data in total intensity for a complete sample of 189 sources with
S(20 GHz)>500 mJy, Galactic latitude |b|>5deg, and declination <-30deg, and
some statistical analysis of the spectral behaviour and variability of this
sample, referred to as the "bright PACO sample". Finally we discuss how these
data could be used to transfer absolute calibrations to ground based telescopes
using the CMB dipole calibrated flux densities measured by the Planck
satellite, and we provide some test fluxes on bright calibrators.Comment: 15 pages, 11 figure. Accepted for publication on MNRAS. Catalogue
availabl
The Planck-ATCA Co-eval Observations (PACO) project: analysis of radio source properties between 5 and 217 GHz
The Planck-ATCA Co-eval Observations (PACO) project has yielded observations
of 464 sources with the Australia Telescope Compact Array (ATCA) between 4.5
and 40 GHz. The main purpose of the project was to investigate the spectral
properties of mm-selected radio sources at frequencies below and overlapping
with the ESA's Planck satellite frequency bands, minimizing the variability
effects by observing almost simultaneously with the first two Planck all-sky
surveys. In this paper we present the whole catalogue of observations in total
intensity. By comparing PACO with the various measures of Planck Catalog of
Compact Sources (PCCS) flux densities we found the best consistency with the
PCCS "detection pipeline" photometry (DETFLUX) that we used to investigate the
spectral properties of sources from 5 to 217 GHz. Of our sources, 91% have
remarkably smooth spectrum, well described by a double power law over the full
range. This suggests a single emitting region, at variance with the notion that
"flat" spectra result from the superposition of the emissions from different
compact regions, self absorbed up to different frequencies. Most of the objects
show a spectral steepening above 30 GHz, consistent with synchrotron emission
becoming optically thin. Thus, the classical dichotomy between
flat-spectrum/compact and steep-spectrum/extended radio sources, well
established at cm wavelengths, breaks down at mm wavelengths. The mm-wave
spectra do not show indications of the spectral break expected as the effect of
"electron ageing", suggesting young source ages.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Early evolution of galaxies and of large-scale structure from CMB experiments
Next generation CMB experiments with arcmin resolution will, for free, lay
the foundations for a real breakthrough on the study of the early evolution of
galaxies and galaxy clusters, thanks to the detection of large samples of
strongly gravitationally lensed galaxies and of proto-clusters of dusty
galaxies up to high redshifts. This has an enormous legacy value. High
resolution follow-up of strongly lensed galaxies will allow the direct
investigation of their structure and kinematics up to z~6, providing direct
information on physical processes driving their evolution. Follow-up of
proto-clusters will allow an observational validation of the formation history
of the most massive dark matter halos up to z~4, well beyond the redshift range
accessible via X-ray or SZ measurements. These experiments will also allow a
giant leap forward in the determination of polarization properties of
extragalactic sources, and will provide a complete census of cold dust
available for star formation in the local universe.Comment: Science white paper submitted to the Astro2020 US Decadal Surve
Radio sources in next-generation CMB surveys
CMB surveys provide, for free, blindly selected samples of extragalactic
radio sources at much higher frequencies than traditional radio surveys.
Next-generation, ground-based CMB experiments with arcmin resolution at mm
wavelengths will provide samples of thousands radio sources allowing the
investigation of the evolutionary properties of blazar populations, the study
of the earliest and latest stages of radio activity, the discovery of rare
phenomena and of new transient sources and events. Space-borne experiments will
extend to sub-mm wavelengths the determinations of the SEDs of many hundreds of
blazars, in temperature and in polarization, allowing us to investigate the
flow and the structure of relativistic jets close to their base, and the
electron acceleration mechanisms. A real breakthrough will be achieved in the
caracterization of the polarization properties. The first direct counts in
polarization will be obtained, enabling a solid assessment of the
extra-galactic source contamination of CMB maps and allowing us to understand
structure and intensity of magnetic fields, particle densities and structures
of emitting regions close to the base of the jet.Comment: Science white paper submitted to the Astro2020 US Decadal Surve
Methodological refinement of the submillimeter galaxy magnification bias. Paper iI: cosmological analysis with a single redshift bin
The main goal of this work, the second in a three-paper series, is to test
the impact of a methodological improvement in measuring the magnification bias
signal on a sample of submillimeter galaxies and its implications for
constraining cosmological parameters. The analysis considers the angular
cross-correlation function between a foreground sample of GAMA galaxies
() and a background sample of H-ATLAS submillimeter galaxies
(). A refined methodology, discussed extensively in Paper I, is
used. By interpreting the weak lensing signal within the halo model and
employing an MCMC algorithm, the posterior distribution of the halo occupation
distribution (HOD) and cosmological parameters is obtained for a flat
CDM model. The analysis incorporates the foreground angular
auto-correlation function to account for galaxy clustering. The results
demonstrate a remarkable improvement in uncertainties for both HOD and
cosmological parameters compared to previous studies. However, when using the
cross-correlation data alone, the estimation of depends on prior
knowledge of , the logarithmic slope of the background number counts.
Assuming a physically motivated prior distribution for , mean values of
and are obtained.
These results may however be subject to an inherent bias in the data due to
anomalous behavior observed in the G15 field. After excluding the G15 region,
the mean values shift to and
. This becomes more apparent when adding the
clustering of the foreground sample, but the dependence on information
disappears, mitigating the aforementioned issue. Excluding the G15 region, the
joint analysis yields mean values of ,
, and .Comment: This work is the second one of a three-paper series. Submitted to A&
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