559 research outputs found
Non-blind catalogue of extragalactic point sources from the Wilkinson Microwave Anisotropy Probe (WMAP) first 3--year survey data
We have used the MHW2 filter to obtain estimates of the flux densities at the
WMAP frequencies of a complete sample of 2491 sources, mostly brighter than 500
mJy at 5 GHz, distributed over the whole sky excluding a strip around the
Galactic equator (b < 5 degrees). After having detected 933 sources above the 3
sigma level in the MHW2 filtered maps - our New Extragalactic WMAP Point Source
(NEWPS_3sigma) Catalogue - we are left with 381 sources above 5 sigma in at
least one WMAP channel, 369 of which constitute our NEWPS_5sigma catalogue. It
is remarkable to note that 98 (i.e. 26%) sources detected above 5 sigma are
`new', they are not present in the WMAP catalogue. Source fluxes have been
corrected for the Eddington bias. Our flux density estimates before such
correction are generally in good agreement with the WMAP ones at 23 GHz. At
higher frequencies WMAP fluxes tend to be slightly higher than ours, probably
because WMAP estimates neglect the deviations of the point spread function from
a Gaussian shape. On the whole, above the estimated completeness limit of 1.1
Jy at 23 GHz we detected 43 sources missed by the blind method adopted by the
WMAP team. On the other hand, our low-frequency selection threshold left out 25
WMAP sources, only 12 of which, however, are 5 sigma detections and only 3 have
fluxes S at 23 GHz > 1.1 Jy. Thus, our approach proved to be competitive with,
and complementary to the WMAP one.Comment: 18 pages, 6 figures, 5 tables. Accepted for publication in ApJ
Filtering techniques for the detection of Sunyaev-Zel'dovich clusters in multifrequency CMB maps
The problem of detecting Sunyaev-Zel'dovich (SZ) clusters in multifrequency
CMB observations is investigated using a number of filtering techniques. A
multifilter approach is introduced, which optimizes the detection of SZ
clusters on microwave maps. An alternative method is also investigated, in
which maps at different frequencies are combined in an optimal manner so that
existing filtering techniques can be applied to the single combined map. The SZ
profiles are approximated by the circularly-symmetric template , with and , where the core radius and the overall amplitude of the effect
are not fixed a priori, but are determined from the data. The background
emission is modelled by a homogeneous and isotropic random field, characterized
by a cross-power spectrum with . The
filtering methods are illustrated by application to simulated Planck
observations of a patch of sky in 10 frequency
channels. Our simulations suggest that the Planck instrument should detect
SZ clusters in 2/3 of the sky. Moreover, we find the catalogue
to be complete for fluxes mJy at 300 GHz.Comment: 12 pages, 7 figures; Corrected figures. Submitted to MNRA
Comparing filters for the detection of point sources
This paper considers filters (the Mexican hat wavelet, the matched and the
scale-adaptive filters) that optimize the detection/separation of point sources
on a background. We make a one-dimensional treatment, we assume that the
sources have a Gaussian profile, i. e. , and a
background modelled by an homogeneous and isotropic Gaussian random field,
characterised by a power spectrum .
Local peak detection is used after filtering. Then, the Neyman-Pearson
criterion is used to define the confidence level for detections and a
comparison of filters is done based on the number of spurious and true
detections. We have performed numerical simulations to test theoretical ideas
and conclude that the results of the simulations agree with the analytical
results.Comment: 17 pages, 17 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
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