316 research outputs found
Statistical properties of dust far-infrared emission
The description of the statistical properties of dust emission gives
important constraints on the physics of the interstellar medium but it is also
a useful way to estimate the contamination of diffuse interstellar emission in
the cases where it is considered a nuisance. The main goals of this analysis of
the power spectrum and non-Gaussian properties of 100 micron dust emission are
1) to estimate the power spectrum of interstellar matter density in three
dimensions, 2) to review and extend previous estimates of the cirrus noise due
to dust emission and 3) to produce simulated dust emission maps that reproduce
the observed statistical properties. The main results are the following. 1) The
cirrus noise level as a function of brightness has been previously
overestimated. It is found to be proportional to instead of ^1.5, where
is the local average brightness at 100 micron. This scaling is in
accordance with the fact that the brightness fluctuation level observed at a
given angular scale on the sky is the sum of fluctuations of increasing
amplitude with distance on the line of sight. 2) The spectral index of dust
emission at scales between 5 arcmin and 12.5 degrees is =-2.9 on average
but shows significant variations over the sky. Bright regions have
systematically steeper power spectra than diffuse regions. 3) The skewness and
kurtosis of brightness fluctuations is high, indicative of strong
non-Gaussianity. 4) Based on our characterization of the 100 micron power
spectrum we provide a prescription of the cirrus confusion noise as a function
of wavelength and scale. 5) Finally we present a method based on a modification
of Gaussian random fields to produce simulations of dust maps which reproduce
the power spectrum and non-Gaussian properties of interstellar dust emission.Comment: 13 pages, 13 figures. Accepted for publication in A&
Detection of new point-sources in WMAP Cosmic Microwave Background (CMB) maps at high Galactic latitude. A new technique to extract point sources from CMB maps
In experimental microwave maps, point-sources can strongly affect the
estimation of the power-spectrum and/or the test of Gaussianity of the Cosmic
Microwave Background (CMB) component. As a consequence, their removal from the
sky maps represents a critical step in the analysis of the CMB data. Before
removing a source, however, it is necessary to detect it and source extraction
consists of a delicate preliminary operation. In the literature, various
techniques have been presented to detect point-sources in the sky maps. The
most sophisticated ones exploit the multi-frequency nature of the observations
that is typical of the CMB experiments. These techniques have "optimal"
theoretical properties and, at least in principle, are capable of remarkable
performances. Actually, they are rather difficult to use and this deteriorates
the quality of the obtainable results. In this paper, we present a new
technique, the "weighted matched filter" (WMF), that is quite simple to use and
hence more robust in practical applications. Such technique shows particular
efficiency in the detection of sources whose spectra have a slope different
from zero. We apply this method to three Southern Hemisphere sky regions - each
with an area of 400 square degrees - of the seven years Wilkinson Microwave
Anisotropy Probe (WMAP) maps and compare the resulting sources with those of
the two seven-year WMAP point-sources catalogues. In these selected regions we
find seven additional sources not previously listed in WMAP catalogues and
discuss their most likely identification and spectral properties.Comment: Astronomy and Astrophysics, 2011, in pres
Digital Deblurring of CMB Maps II: Asymmetric Point Spread Function
In this second paper in a series dedicated to developing efficient numerical
techniques for the deblurring Cosmic Microwave Background (CMB) maps, we
consider the case of asymmetric point spread functions (PSF). Although
conceptually this problem is not different from the symmetric case, there are
important differences from the computational point of view because it is no
longer possible to use some of the efficient numerical techniques that work
with symmetric PSFs. We present procedures that permit the use of efficient
techniques even when this condition is not met. In particular, two methods are
considered: a procedure based on a Kronecker approximation technique that can
be implemented with the numerical methods used with symmetric PSFs but that has
the limitation of requiring only mildly asymmetric PSFs. The second is a
variant of the classic Tikhonov technique that works even with very asymmetric
PSFs but that requires discarding the edges of the maps. We provide details for
efficient implementations of the algorithms. Their performance is tested on
simulated CMB maps.Comment: 9 pages, 13 Figure
An approach for the detection of point-sources in very high resolution microwave maps
This paper deals with the detection problem of extragalactic point-sources in
multi-frequency, microwave sky maps that will be obtainable in future cosmic
microwave background radiation (CMB) experiments with instruments capable of
very high spatial resolution. With spatial resolutions that can be of order of
0.1-1.0 arcsec or better, the extragalactic point-sources will appear isolated.
The same holds also for the compact structures due to the Sunyaev-Zeldovich
(SZ) effect (both thermal and kinetic). This situation is different from the
maps obtainable with instruments as WMAP or PLANCK where, because of the
smaller spatial resolution (approximately 5-30 arcmin), the point-sources and
the compact structures due to the SZ effect form a uniform noisy background
(the "confusion noise"). Hence, the point-source detection techniques developed
in the past are based on the assumption that all the emissions that contribute
to the microwave background can be modeled with homogeneous and isotropic
(often Gaussian) random fields and make use of the corresponding spatial
power-spectra. In the case of very high resolution observations such an
assumption cannot be adopted since it still holds only for the CMB. Here, we
propose an approach based on the assumption that the diffuse emissions that
contribute to the microwave background can be locally approximated by
two-dimensional low order polynomials. In particular, two sets of numerical
techniques are presented containing two different algorithms each. The
performance of the algorithms is tested with numerical experiments that mimic
the physical scenario expected for high Galactic latitude observations with the
Atacama Large Millimeter/Submillimeter Array (ALMA).Comment: Accepted for publication on "Astronomy & Astrophysics". arXiv admin
note: substantial text overlap with arXiv:1206.4536 Replaced version is the
accepted one and published in A&
The Dependence of Galaxy Shape on Luminosity and Surface Brightness Profile
For a sample of 96,951 galaxies from the Sloan Digital Sky Survey Data
Release 3, we study the distribution of apparent axis ratios as a function of
r-band absolute magnitude and surface brightness profile type. We use the
parameter fracDeV to quantify the profile type (fracDeV = 1 for a de
Vaucouleurs profile; fracDeV = 0 for an exponential profile). When the apparent
axis ratio q_{am} is estimated from the moments of the light distribution, the
roundest galaxies are very bright (M_r \sim -23) de Vaucouleurs galaxies and
the flattest are modestly bright (M_r \sim -18) exponential galaxies. When the
apparent axis ratio q_{25} is estimated from the axis ratio of the 25
mag/arcsec^2 isophote, we find that de Vaucouleurs galaxies are flatter than
exponential galaxies of the same absolute magnitude. For a given surface
brightness profile type, very bright galaxies are rounder, on average, than
fainter galaxies. We deconvolve the distributions of apparent axis ratios to
find the distribution of the intrinsic short-to-long axis ratio gamma, assuming
constant triaxiality T. For all profile types and luminosities, the
distribution of apparent axis ratios is inconsistent with a population of
oblate spheroids, but is usually consistent with a population of prolate
spheroids. Bright galaxies with a de Vaucouleurs profile (M_r < -21.84, fracDeV
> 0.9) have a distribution of q_{am} that is consistent with triaxiality in the
range 0.4 < T < 0.8, with mean intrinsic axis ratio 0.66 < gamma < 0.69. The
fainter de Vaucouleurs galaxies are best fit with prolate spheroids (T = 1)
with mean axis ratio gamma = 0.51.Comment: 32 pages, 12 figures, to appear in Ap
Digital Deblurring of CMB Maps: Performance and Efficient Implementation
Digital deblurring of images is an important problem that arises in
multifrequency observations of the Cosmic Microwave Background (CMB) where,
because of the width of the point spread functions (PSF), maps at different
frequencies suffer a different loss of spatial resolution. Deblurring is useful
for various reasons: first, it helps to restore high frequency components lost
through the smoothing effect of the instrument's PSF; second, emissions at
various frequencies observed with different resolutions can be better studied
on a comparable resolution; third, some map-based component separation
algorithms require maps with similar level of degradation. Because of
computational efficiency, deblurring is usually done in the frequency domain.
But this approach has some limitations as it requires spatial invariance of the
PSF, stationarity of the noise, and is not flexible in the selection of more
appropriate boundary conditions. Deblurring in real space is more flexible but
usually not used because of its high computational cost. In this paper (the
first in a series on the subject) we present new algorithms that allow the use
of real space deblurring techniques even for very large images. In particular,
we consider the use of Tikhonov deblurring of noisy maps with applications to
{\it PLANCK}. We provide details for efficient implementations of the
algorithms. Their performance is tested on Gaussian and non-Gaussian simulated
CMB maps, and PSFs with both circular and elliptical symmetry. Matlab code is
made available.Comment: 14 pages, 16, figures, A&A in press; high quality figures available
upon request to the author
Antifungal and antimycobacterial activity of new N1-[1-aryl-2-(1H-Imidazol-1-yl and 1H-1,2,4-triazol-1-yl)-ethylidene]-pyridine-2-carboxamidrazone derivatives: A combined experimental and computational approach.
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