999 research outputs found

### Circular scans for CMB anisotropy observation and analysis

A number of experiments for measuring anisotropies of the Cosmic Microwave
Background use scanning strategies in which temperature fluctuations are
measured along circular scans on the sky. It is possible, from a large number
of such intersecting circular scans, to build two-dimensional sky maps for
subsequent analysis. However, since instrumental effects --- especially the
excess low-frequency 1/f noise --- project onto such two-dimensional maps in a
non-trivial way, we discuss the analysis approach which focuses on information
contained in the individual circular scans. This natural way of looking at CMB
data from experiments scanning on the circles combines the advantages of
elegant simplicity of Fourier series for the computation of statistics useful
for constraining cosmological scenarios,and superior efficiency in analysing
and quantifying most of the crucial instrumental effects.Comment: 10 pages, 5 figures (.ps), submitted to MNRA

### Three-Point Statistics from a New Perspective

Multipole expansion of spatial three-point statistics is introduced as a tool
for investigating and displaying configuration dependence. The novel
parametrization renders the relation between bi-spectrum and three-point
correlation function especially transparent as a set of two-dimensional Hankel
transforms. It is expected on theoretical grounds, that three-point statistics
can be described accurately with only a few multipoles. In particular, we show
that in the weakly non-linear regime, the multipoles of the reduced bispectrum,
$Q_l$, are significant only up to quadrupole. Moreover, the non-linear bias in
the weakly non-linear regime only affects the monopole order of these
statistics. As a consequence, a simple, novel set of estimators can be
constructed to constrain galaxy bias. In addition, the quadrupole to dipole
ratio is independent of the bias, thus it becomes a novel diagnostic of the
underlying theoretical assumptions: weakly non-linear gravity and perturbative
local bias. To illustrate the use of our approach, we present predictions based
on both power law, and CDM models. We show that the presently favoured
SDSS-WMAP concordance model displays strong ``baryon bumps'' in the $Q_l$'s.
Finally, we sketch out three practical techniques estimate these novel
quantities: they amount to new, and for the first time edge corrected,
estimators for the bispectrum.Comment: 5 pages 6 figures, ApL accepte

### The FIR/submm window on galaxy formation

Our view on the deep universe has been so far biased towards optically bright
galaxies. Now, the measurement of the Cosmic Infrared Background in FIRAS and
DIRBE residuals, and the observations of FIR/submm sources by the ISOPHOT and
SCUBA instruments begin unveiling the ``optically dark side'' of galaxy
formation. Though the origin of dust heating is still unsolved, it appears very
likely that a large fraction of the FIR/submm emission is due to
heavily-extinguished star formation. Consequently, the level of the CIRB
implies that about 2/3 of galaxy/star formation in the universe is hidden by
dust shrouds. In this review, we introduce a new modeling of galaxy formation
and evolution that provides us with specific predictions in FIR/submm
wavebands. These predictions are compared with the current status of the
observations. Finally, the capabilities of current and forthcoming instruments
for all-sky and deep surveys of FIR/submm sources are briefly described.Comment: 10 pages, Latex, 5 postscript figures, to appear in ``The Birth of
Galaxies'', 1999, B. Guiderdoni, F.R. Bouchet, T.X. Thuan & J. Tran Thanh Van
(eds), Editions Frontiere

### Previrialization

We propose a method to solve the "previrialization" problem of whether the non-linear interactions between perturbations at different scales increase or decrease the rate of growth of structure. As a measure of this effect we calculate the weakly non-linear corrections to the variance of the probability distribution function of the density field. We assume Gaussian initial conditions and use perturbative expansions to calculate these corrections for scale-free initial power spectra. As a realistic example, we also compute the corrections for the spectrum proposed by Peacock \& Dodds (1994). The calculations are performed for both a Gaussian and a top-hat smoothing of the evolved fields. We show that the effect of weakly non-linear interactions depends strongly on the spectral index; they increase the variance for the spectral index n=-2, but decrease it for n \ge -1. Finally, we compare our perturbative calculations to N-body simulations and a formula of a type proposed by Hamilton et al. (1991)

### Semi-analytic modelling of galaxy evolution in the IR/submm range

This paper proposes a new semi-analytic modelling of galaxy properties in the
IR/submm wavelength range, which is explicitly set in a cosmological framework.
This type of approach has had some success in reproducing the optical
properties of galaxies. We hereafter propose a simple extension to the IR/submm
range. We estimate the IR/submm luminosities of ``luminous UV/IR galaxies'',
and we explore how much star formation could be hidden in
heavily--extinguished, ``ultraluminous IR galaxies'' by designing a family of
evolutionary scenarios which are consistent with the current status of the
``cosmic constraints'', as well as with the IRAS luminosity function and faint
counts, but with different high-z IR luminosity densities. However, these
scenarios generate a Cosmic Infrared Background whose spectrum falls within the
range of the isotropic IR component detected by Puget et al. (1996) and
revisited by Guiderdoni et al. (1997). We give predictions for the faint galaxy
counts and redshift distributions at IR and submm wavelengths. The submm range
is very sensitive to the details of the evolutionary scenarios. As a result,
the on-going and forthcoming observations with ISO and SCUBA (and later with
SIRTF, SOFIA, FIRST and PLANCK) will put strong constraints on the evolution of
galaxies at z=1 and beyond.Comment: 21 pages, Latex, 20 postscript figures, accepted for publication in
Month. Not. Roy. Astron. So

### Reconstructing the shape of the correlation function

We develop an estimator for the correlation function which, in the ensemble
average, returns the shape of the correlation function, even for signals that
have significant correlations on the scale of the survey region. Our estimator
is general and works in any number of dimensions. We develop versions of the
estimator for both diffuse and discrete signals. As an application, we examine
Monte Carlo simulations of X-ray background measurements. These include a
realistic, spatially-inhomogeneous population of spurious detector events. We
discuss applying the estimator to the averaging of correlation functions
evaluated on several small fields, and to other cosmological applications.Comment: 10 pages, 5 figures, submitted to ApJS. Methods and results unchanged
but text is expanded and significantly reordered in response to refere

### Cosmic microwave background power spectrum estimation with the destriping technique

Extraction of the CMB (Cosmic Microwave Background) angular power spectrum is
a challenging task for current and future CMB experiments due to the large data
sets involved. Here we describe an implementation of MASTER (Monte carlo
Apodised Spherical Transform EstimatoR) which exploits the destriping technique
as a map-making method. In this method a noise estimate based on destriped
noise-only MC (Monte Carlo) simulations is subtracted from the pseudo angular
power spectrum. As a working case we use realistic simulations of the PLANCK
LFI (Low Frequency Instrument). We found that the effect of destriping on a
pure sky signal is minimal and requires no correction. Instead we found an
effect related to the distribution of detector pointings, which affects the
high multipole part of the power spectrum. We correct for this by subtracting a
``signal bias'' estimated by MC simulations. We also give analytical estimates
for this signal bias. Our method is fast and accurate enough (the estimator is
un-biased and errors are close to theoretical expectations for maximal
accuracy) to estimate the CMB angular power spectra for current and future CMB
space missions. This study is related to PLANCK LFI activities.Comment: 16 pages, 23 figures, submitted to MNRA

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