194 research outputs found
High angular resolution observation of the Sunyaev-Zel'dovich effect in the massive z=0.83 cluster ClJ0152-1357
X-ray observations of galaxy clusters at high redshift (z>0.5) indicate that
they are more morphologically complex and less virialized than those at
low-redshift. We present the first subarcmin resolution at 18 GHz observations
of the Sunyaev-Zel'dovich (SZ) effect for ClJ0152-1357 using the Australia
Telescope Compact Array. ClJ0152-1357 is a massive cluster at redshift z=0.83
and has a complex structure including several merging subclumps which have been
studied at optical, X-ray, and radio wavelengths. Our high-resolution
observations indicate a clear displacement of the maximum SZ effect from the
peak of X-ray emission for the most massive sub-clump. This result shows that
the cluster gas within the cluster substructures is not virialised in
ClJ0152-1357 and we suggest that it is still recovering from a recent merger
event. A similar offset of the SZ effect has been recently seen in the `bullet
cluster' by Malu et al. This non-equilibrium situation implies that high
resolution observations are necessary to investigate galaxy cluster evolution,
and to extract cosmological constraints from a comparison of the SZ effect and
X-ray signals.Comment: 5 pages, 4 figures, submitted to ApJ
A polarization survey of bright extragalactic AT20G sources
We present polarization data for 180 extragalactic sources extracted from the Australia Telescope 20 GHz (AT20G) survey catalogue and observed with the Australia Telescope Compact Array during a dedicated, high sensitivity run (σP ∼ 1 mJy). For the sake of completeness, we extracted the polarization information for seven extended sources from the 9 yr Wilkinson Microwave Anisotropy Probe co-added maps at 23 GHz. The full sample of 187 sources constitutes a ≃99 per cent complete sample of extragalactic sources brighter than S20GHz = 500 mJy at the selection epoch with declination δ < −30°. The sample has a 91.4 per cent detection rate in polarization at ∼20 GHz (94 per cent if considering the subsample of point-like sources). We have measurements also at 4.8 and 8.6 GHz within ∼1 month of the 20 GHz observations for 172 sources to reconstruct the spectral properties of the sample in total intensity and in polarization: 143 of them have a polarization detection at all three frequencies.
We find that there is no statistically significant evidence of a relationship either between the fraction of polarization and frequency or between the fraction of polarization and the total intensity flux density. This indicates that Faraday depolarization is not very important above 4.8 GHz and that the magnetic field is not substantially more ordered in the regions dominating the emission at higher frequencies (up to 20 GHz). We estimate the distribution of the polarization fraction and the polarized flux density source counts at ∼20 GHz
Wide-Field Imaging and Polarimetry for the Biggest and Brightest in the 20GHz Southern Sky
We present wide-field imaging and polarimetry at 20GHz of seven of the most
extended, bright (Stot >= 0.50 Jy), high-frequency selected radio sources in
the southern sky with declinations < -30 deg. Accompanying the data are brief
reviews of the literature for each source, The results presented here aid in
the statistical completeness of the Australia Telescope 20GHz Survey's bright
source sample. The data are of crucial interest for future cosmic microwave
background missions as a collection of information about candidate calibrator
sources. We are able to obtain data for seven of the nine sources identified by
our selection criteria. We report that Pictor A is thus far the best
extragalactic calibrator candidate for the Low Frequency Instrument of the
Planck European Space Agency mission due to its high level of integrated
polarized flux density (0.50+/-0.06 Jy) on a scale of 10 arcmin. Six of the
seven sources have a clearly detected compact radio core, with either a null or
less than two percent detection of polarized emission from the nucleus. Most
sources with detected jets have magnetic field alignments running in a
longitudinal configuration, however PKS1333-33 exhibits transverse fields and
an orthogonal change in field geometry from nucleus to jets.Comment: 17 pages, 9 figures, 2 table
Constraining Primordial Non-Gaussianity with High-Redshift Probes
We present an analysis of the constraints on the amplitude of primordial
non-Gaussianity of local type described by the dimensionless parameter . These constraints are set by the auto-correlation functions (ACFs) of two
large scale structure probes, the radio sources from NRAO VLA Sky Survey (NVSS)
and the quasar catalogue of Sloan Digital Sky Survey Release Six (SDSS DR6
QSOs), as well as by their cross-correlation functions (CCFs) with the cosmic
microwave background (CMB) temperature map (Integrated Sachs-Wolfe effect).
Several systematic effects that may affect the observational estimates of the
ACFs and of the CCFs are investigated and conservatively accounted for. Our
approach exploits the large-scale scale-dependence of the non-Gaussian halo
bias. The derived constraints on {} coming from the NVSS CCF and
from the QSO ACF and CCF are weaker than those previously obtained from the
NVSS ACF, but still consistent with them. Finally, we obtain the constraints on
() and () from
NVSS data and SDSS DR6 QSO data, respectively.Comment: 16 pages, 8 figures, 1 table, Accepted for publication on JCA
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths
We present the Planck Sky Model (PSM), a parametric model for the generation
of all-sky, few arcminute resolution maps of sky emission at submillimetre to
centimetre wavelengths, in both intensity and polarisation. Several options are
implemented to model the cosmic microwave background, Galactic diffuse emission
(synchrotron, free-free, thermal and spinning dust, CO lines), Galactic H-II
regions, extragalactic radio sources, dusty galaxies, and thermal and kinetic
Sunyaev-Zeldovich signals from clusters of galaxies. Each component is
simulated by means of educated interpolations/extrapolations of data sets
available at the time of the launch of the Planck mission, complemented by
state-of-the-art models of the emission. Distinctive features of the
simulations are: spatially varying spectral properties of synchrotron and dust;
different spectral parameters for each point source; modeling of the clustering
properties of extragalactic sources and of the power spectrum of fluctuations
in the cosmic infrared background. The PSM enables the production of random
realizations of the sky emission, constrained to match observational data
within their uncertainties, and is implemented in a software package that is
regularly updated with incoming information from observations. The model is
expected to serve as a useful tool for optimizing planned microwave and
sub-millimetre surveys and to test data processing and analysis pipelines. It
is, in particular, used for the development and validation of data analysis
pipelines within the planck collaboration. A version of the software that can
be used for simulating the observations for a variety of experiments is made
available on a dedicated website.Comment: 35 pages, 31 figure
High-energy sources at low radio frequency : the Murchison Widefield Array view of Fermi blazars
This is the accepted version of the following article: Giroletti, M. et al., A&A, 588 (2016) A141, which has been published in final form at DOI: http://dx.doi.org/10.1051/0004-6361/201527817. This article may be used for non-commercial purposes in accordance with the EDP Sciences self-archiving policies.Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. We characterize the spectral properties of the blazar population at low radio frequency compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6,100 deg^2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detected by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by \fermilat. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120--180 MHz) blazar spectral index is : blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.Peer reviewedFinal Published versio
Simultaneous Planck, Swift, and Fermi observations of X-ray and gamma-ray selected blazars
We present simultaneous Planck, Swift, Fermi, and ground-based data for 105
blazars belonging to three samples with flux limits in the soft X-ray, hard
X-ray, and gamma-ray bands. Our unique data set has allowed us to demonstrate
that the selection method strongly influences the results, producing biases
that cannot be ignored. Almost all the BL Lac objects have been detected by
Fermi-LAT, whereas ~40% of the flat-spectrum radio quasars (FSRQs) in the
radio, soft X-ray, and hard X-ray selected samples are still below the
gamma-ray detection limit even after integrating 27 months of Fermi-LAT data.
The radio to sub-mm spectral slope of blazars is quite flat up to ~70GHz, above
which it steepens to ~-0.65. BL Lacs have significantly flatter spectra
than FSRQs at higher frequencies. The distribution of the rest-frame
synchrotron peak frequency (\nupS) in the SED of FSRQs is the same in all the
blazar samples with =10^13.1 Hz, while the mean inverse-Compton peak
frequency, , ranges from 10^21 to 10^22 Hz. The distributions of \nupS
and of \nupIC of BL Lacs are much broader and are shifted to higher energies
than those of FSRQs and strongly depend on the selection method. The Compton
dominance of blazars ranges from ~0.2 to ~100, with only FSRQs reaching values
>3. Its distribution is broad and depends strongly on the selection method,
with gamma-ray selected blazars peaking at ~7 or more, and radio-selected
blazars at values ~1, thus implying that the assumption that the blazar power
is dominated by high-energy emission is a selection effect. Simple SSC models
cannot explain the SEDs of most of the gamma-ray detected blazars in all
samples. The SED of the blazars that were not detected by Fermi-LAT may instead
be consistent with SSC emission. Our data challenge the correlation between
bolometric luminosity and \nupS predicted by the blazar sequence.Comment: Version accepted by A&A. Joint Planck, Swift, and Fermi
collaborations pape
Component separation methods for the Planck mission
The Planck satellite will map the full sky at nine frequencies from 30 to 857
GHz. The CMB intensity and polarization that are its prime targets are
contaminated by foreground emission. The goal of this paper is to compare
proposed methods for separating CMB from foregrounds based on their different
spectral and spatial characteristics, and to separate the foregrounds into
components of different physical origin. A component separation challenge has
been organized, based on a set of realistically complex simulations of sky
emission. Several methods including those based on internal template
subtraction, maximum entropy method, parametric method, spatial and harmonic
cross correlation methods, and independent component analysis have been tested.
Different methods proved to be effective in cleaning the CMB maps from
foreground contamination, in reconstructing maps of diffuse Galactic emissions,
and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power
spectrum of the residuals is, on the largest scales, four orders of magnitude
lower than that of the input Galaxy power spectrum at the foreground minimum.
The CMB power spectrum was accurately recovered up to the sixth acoustic peak.
The point source detection limit reaches 100 mJy, and about 2300 clusters are
detected via the thermal SZ effect on two thirds of the sky. We have found that
no single method performs best for all scientific objectives. We foresee that
the final component separation pipeline for Planck will involve a combination
of methods and iterations between processing steps targeted at different
objectives such as diffuse component separation, spectral estimation and
compact source extraction.Comment: Matches version accepted by A&A. A version with high resolution
figures is available at http://people.sissa.it/~leach/compsepcomp.pd
Follow-up observations at 16 and 33 GHz of extragalactic sources from WMAP 3-year data: I - Spectral properties
We present follow-up observations of 97 point sources from the Wilkinson
Microwave Anisotropy Probe (WMAP) 3-year data, contained within the New
Extragalactic WMAP Point Source (NEWPS) catalogue between declinations of -4
and +60 degrees; the sources form a flux-density-limited sample complete to 1.1
Jy (approximately 5 sigma) at 33 GHz. Our observations were made at 16 GHz
using the Arcminute Microkelvin Imager (AMI) and at 33 GHz with the Very Small
Array (VSA). 94 of the sources have reliable, simultaneous -- typically a few
minutes apart -- observations with both telescopes. The spectra between 13.9
and 33.75 GHz are very different from those of bright sources at low frequency:
44 per cent have rising spectra (alpha < 0.0), where flux density is
proportional to frequency^-alpha, and 93 per cent have spectra with alpha <
0.5; the median spectral index is 0.04. For the brighter sources, the agreement
between VSA and WMAP 33-GHz flux densities averaged over sources is very good.
However, for the fainter sources, the VSA tends to measure lower values for the
flux densities than WMAP. We suggest that the main cause of this effect is
Eddington bias arising from variability.Comment: 12 pages, 13 figures, submitted to MNRA
Herschel *-ATLAS: Deep HST/WFC3 imaging of strongly lensed submillimetre galaxies
M. Negrello et al.We report on deep near-infrared observations obtained with the Wide Field Camera-3 (WFC3) onboard the Hubble Space Telescope (HST) of the first five confirmed gravitational lensing events discovered by the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We succeed in disentangling the background galaxy from the lens to gain separate photometry of the two components. The HST data allow us to significantly improve on previous constraints of the mass in stars of the lensed galaxy and to perform accurate lens modelling of these systems, as described in the accompanying paper by Dye et al. We fit the spectral energy distributions of the background sources from near-IR to millimetre wavelengths and use the magnification factors estimated by Dye et al. to derive the intrinsic properties of the lensed galaxies. We find these galaxies to have star-formations rates (SFR) ~ 400-2000 M⊙ yr-1, with ~(6-25) × 1010 M⊙ of their baryonic mass already turned into stars. At these rates of star formation, all remaining molecular gas will be exhausted in less than ~100 Myr, reaching a final mass in stars of a few 1011 M⊙. These galaxies are thus proto-ellipticals caught during their major episode of star formation, and observed at the peak epoch (z ~ 1.5-3) of the cosmic star formation history of the Universe.This work was supported by STFC (grants PP/D002400/1 and ST/G002533/1), by ASI/INAF agreement I/072/09/0, by PRININAF 2012 project ‘Looking into the dust-obscured phase of galaxy formation through cosmic zoom lenses in the Herschel Astrophysical Large Area Survey’ and, in part, by the Spanish Ministerio de Ciencia e Innovacion (project AYA2010-21766-C03-01). JGN acknowledges financial support from the Spanish CSIC for a JAE-DOC fellowship, co-funded by the European Social Fund.Peer Reviewe
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