480 research outputs found
Biparametric Adaptive Filter: detection of compact sources in complex microwave backgrounds
In this article we consider the detection of compact sources in maps of the
Cosmic Microwave Background radiation (CMB) following the philosophy behind the
Mexican Hat Wavelet Family (MHWn) of linear filters. We present a new
analytical filter, the Biparametric Adaptive Filter (BAF), that is able to
adapt itself to the statistical properties of the background as well as to the
profile of the compact sources, maximizing the amplification and improving the
detection process. We have tested the performance of this filter using
realistic simulations of the microwave sky between 30 and 857 GHz as observed
by the Planck satellite, where complex backgrounds can be found. We demonstrate
that doing a local analysis on flat patches allows one to find a combination of
the optimal scale of the filter R and the index of the filter g that will
produce a global maximum in the amplification, enhancing the signal-to-noise
ratio (SNR) of the detected sources in the filtered map and improving the total
number of detections above a threshold. We conclude that the new filter is able
to improve the overall performance of the MHW2, increasing the SNR of the
detections and, therefore, the number of detections above a 5 sigma threshold.
The improvement of the new filter in terms of SNR is particularly important in
the vicinity of the galactic plane and in the presence of strong galactic
emission. Finally, we compare the sources detected by each method and find that
the new filter is able to detect more new sources than the MHW2 at all
frequencies and in clean regions of the sky. The BAF is also less affected by
spurious detections, associated to compact structures in the vicinity of the
galactic plane.Comment: 17 pages, 15 figures and 3 tables. Accepted for publication in MNRA
Detection/estimation of the modulus of a vector. Application to point source detection in polarization data
Given a set of images, whose pixel values can be considered as the components
of a vector, it is interesting to estimate the modulus of such a vector in some
localised areas corresponding to a compact signal. For instance, the
detection/estimation of a polarized signal in compact sources immersed in a
background is relevant in some fields like astrophysics. We develop two
different techniques, one based on the Neyman-Pearson lemma, the Neyman-Pearson
filter (NPF), and another based on prefiltering-before-fusion, the filtered
fusion (FF), to deal with the problem of detection of the source and estimation
of the polarization given two or three images corresponding to the different
components of polarization (two for linear polarization, three including
circular polarization). For the case of linear polarization, we have performed
numerical simulations on two-dimensional patches to test these filters
following two different approaches (a blind and a non-blind detection),
considering extragalactic point sources immersed in cosmic microwave background
(CMB) and non-stationary noise with the conditions of the 70 GHz \emph{Planck}
channel. The FF outperforms the NPF, especially for low fluxes. We can detect
with the FF extragalactic sources in a high noise zone with fluxes >=
(0.42,0.36) Jy for (blind/non-blind) detection and in a low noise zone with
fluxes >= (0.22,0.18) Jy for (blind/non-blind) detection with low errors in the
estimated flux and position.Comment: 11 pages, 5 figure
A multifrequency method based on the Matched Multifilter for the detection of point sources in CMB maps
In this work we deal with the problem of simultaneous multifrequency
detection of extragalactic point sources in maps of the Cosmic Microwave
Background. We apply a linear filtering technique that uses spatial information
and the cross-power spectrum. To make this, we simulate realistic and
non-realistic flat patches of the sky at two frequencies of Planck: 44 and 100
GHz. We filter to detect and estimate the point sources and compare this
technique with the monofrequency matched filter in terms of completeness,
reliability, flux and spectral index accuracy. The multifrequency method
outperforms the matched filter at the two frequencies and in all the studied
cases in the work.Comment: 14 pages, 6 figures, 1 tabl
Herschel-ATLAS: Evolution of the 250 µm luminosity function out to z = 0.5
5 páginas, 4 figuras.-- Herschel is an ESA space observatory with science instruments
provided by European-led Principal Investigator consortia and with important
participation from NASA.-- et al.We have determined the luminosity function of 250 μm-selected galaxies detected in the ~14 deg2 science demonstration region of the Herschel-ATLAS project out to a redshift of z = 0.5. Our findings very clearly show that the luminosity function evolves steadily out to this redshift. By selecting a sub-group of sources within a fixed luminosity interval where incompleteness effects are minimal, we have measured a smooth increase in the comoving 250 μm luminosity density out to z = 0.2 where it is 3.6+1.4-0.9 times higher than the local value.S.D. Acknowledges the UK STFC for support.Peer reviewe
A novel multi-frequency technique for the detection of point sources in Cosmic Microwave Background maps
In this work we address the problem of simultaneous multi-frequency detection
of extragalactic point sources in maps of the Cosmic Microwave Background. We
apply a new linear filtering technique, the so called `matched matrix filters',
that incorporates full spatial information, including the cross-correlation
among channels, without making any a priori assumption about the spectral
behaviour of the sources. A substantial reduction of the background is achieved
thanks to the optimal combination of filtered maps. We describe in detail the
new technique and we apply it to the detection/estimation of radio sources in
realistic all-sky Planck simulations at 30, 44, 70 and 100 GHz. Then we compare
the results with the mono-frequential approach based on the standard matched
filter, in terms of reliability, completeness and flux accuracy of the
resulting point source catalogs. The new filters outperform the standard
matched filters for all these indexes at 30, 44 and 70 GHz, whereas at 100 GHz
both kind of filters have a similar performance. We find a noticeable increment
of the number of true detections for a fixed reliability level. In particular,
for a 95% reliability we practically double the number of detections at 30, 44
and 70 GHz.Comment: 12 pages, 10 figures, submitted to MNRA
Polarization of the WMAP Point Sources
The detection of polarized sources in the WMAP 5-year data is a very
difficult task. The maps are dominated by instrumental noise and only a handful
of sources show up as clear peaks in the Q and U maps. Optimal linear filters
applied at the position of known bright sources detect with a high level of
significance a polarized flux P from many more sources, but estimates of P are
liable to biases. Using a new technique, named the "filtered fusion technique",
we have detected in polarization, with a significance level greater than 99.99%
in at least one WMAP channel, 22 objects, 5 of which, however, do not have a
plausible low radio frequency counterpart and are therefore doubtful. Estimated
polarized fluxes P < 400 mJy at 23 GHz were found to be severely affected by
the Eddington bias. The corresponding polarized flux limit for Planck/LFI at 30
GHz, obtained via realistic simulations, is 300 mJy. We have also obtained
statistical estimates of, or upper limits to the mean polarization degrees of
bright WMAP sources at 23, 33, 41, and 61 GHz, finding that they are of a few
percent.Comment: 10 pages, 6 figures. Accepted for publication in Ap
Absolute calibration of the radio astronomy flux density scale at 22 to 43 GHz using Planck
arXiv:1506.02892v2.-- et al.The Planck mission detected thousands of extragalactic radio sources at frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense that it is based on the satellite's annual motion around the Sun and the temperature of the cosmic microwave background), and its beams are well characterized at sub-percent levels. Thus, Planck's flux density measurements of compact sources are absolute in the same sense. We have made coordinated Very Large Array (VLA) and Australia Telescope Compact Array (ATCA) observations of 65 strong, unresolved Planck sources in order to transfer Planck's calibration to ground-based instruments at 22, 28, and 43 GHz. The results are compared to microwave flux density scales currently based on planetary observations. Despite the scatter introduced by the variability of many of the sources, the flux density scales are determined to 1%-2% accuracy. At 28 GHz, the flux density scale used by the VLA runs 2%-3% ± 1.0% below Planck values with an uncertainty of at 43 GHz, the discrepancy increases to 5%-6% ± 1.4% for both ATCA and the VLA.MLC acknowledges the Spanish MINECO Projects AYA2012-39475-C02-01 and Consolider Ingenio 2010 CSD2010-00064. The Planck Collaboration acknowledges the support of: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MINECO, JA, and RES
(Spain); Tekes, AoF, and CSC (Finland); DLR and MPG(Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); ERC and PRACE (EU).Peer Reviewe
Statistical properties of extragalactic sources in the New Extragalactic WMAP Point Source (NEWPS) catalogue
We present results on spectral index distributions, number counts, redshift
distribution and other general statistical properties of extragalactic point
sources in the NEWPS5 sample L\'opez-Caniego et al. (2007). The flux
calibrations at all the WMAP channels have been reassessed both by comparison
with ground based observations and through estimates of the effective beam
areas. The two methods yield consistent statistical correction factors. A
search of the NED has yielded optical identifications for 89% of sources in the
complete sub-sample of 252 sources with S/N>5 and S>1.1 Jy at 23 GHz; 5 sources
turned out to be Galactic and were removed. The NED also yielded redshifts for
92% of the extragalactic sources at |b|>10deg. Their distribution was compared
with model predictions; the agreement is generally good but a possible
discrepancy is noted. Using the 5 GHz fluxes from the GB6 or PMN surveys, we
find that 76% of the 191 extragalactic sources with S_23GHz>1.3,Jy can be
classified as flat-spectrum sources between 5 and 23 GHz. A spectral steepening
is observed at higher frequencies: only 59% of our sources are still
flat-spectrum sources between 23 and 61 GHz and the average spectral indexes
steepen from = 0.01\pm 0.03 to = 0.37\pm 0.03. We
think, however, that the difference may be due to a selection effect. The
source number counts have a close to Euclidean slope and are in good agreement
with the predictions of the cosmological evolution model by De Zotti et al.
(2005). The observed spectral index distributions were exploited to get
model-independent extrapolations of counts to higher frequencies. The risks of
such operations are discussed and reasons of discrepancies with other recent
estimates are clarified.Comment: 8 pages, 4 figures. Accepted for publication in MNRA
The estimation of the SZ effects with unbiased multifilters
In this work we study the performance of linear multifilters for the
estimation of the amplitudes of the thermal and kinematic Sunyaev-Zel'dovich
effects. We show that when both effects are present, estimation of these
effects with standard matched multifilters is intrinsically biased. This bias
is due to the fact that both signals have basically the same spatial profile.
We find a new family of multifilters related to the matched multifilters that
cancel this systematic bias, hence we call them Unbiased Matched Multifilters.
We test the unbiased matched multifilters and compare them with the standard
matched multifilters using simulations that reproduce the future Planck
mission's observations. We find that in the case of the standard matched
multifilters the systematic bias in the estimation of the kinematic
Sunyaev-Zel'dovich effect can be very large, even greater than the statistical
error bars. Unbiased matched multifilters cancel effectively this kind of bias.
In concordance with other works in the literature, our results indicate that
the sensitivity and resolution of Planck will not be enough to give reliable
estimations of the kinematic Sunyaev-Zel'dovich of individual clusters.
However, since the estimation with the unbiased matched multifilters is not
intrinsically biased, it can be possible to use them to statistically study
peculiar velocities in large scales using large sets of clusters.Comment: 12 pages, 6 figures, submitted to MNRA
Absolute Calibration of the Radio Astronomy Flux Density Scale at 22 to 43 GHz Using Planck
The Planck mission detected thousands of extragalactic radio sources at
frequencies from 28 to 857 GHz. Planck's calibration is absolute (in the sense
that it is based on the satellite's annual motion around the Sun and the
temperature of the cosmic microwave background), and its beams are well
characterized at sub-percent levels. Thus Planck's flux density measurements of
compact sources are absolute in the same sense. We have made coordinated VLA
and ATCA observations of 65 strong, unresolved Planck sources in order to
transfer Planck's calibration to ground-based instruments at 22, 28, and 43
GHz. The results are compared to microwave flux density scales currently based
on planetary observations. Despite the scatter introduced by the variability of
many of the sources, the flux density scales are determined to 1-2% accuracy.
At 28 GHz, the flux density scale used by the VLA runs 3.6% +- 1.0% below
Planck values; at 43 GHz, the discrepancy increases to 6.2% +- 1.4% for both
ATCA and the VLA.Comment: 16 pages, 4 figures and 4 table
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