32 research outputs found
CMB Anisotropies, Cosmological Parameters and Fundamental Physics: Current Status & Perspectives
I describe briefly the Cosmic Microwave Background (hereafter CMB) physics
which explains why high accuracy observations of its spatial structure are a
unique observational tool both for the determination of the global cosmological
parameters and to constrain observationally the physics of the early universe.
I also briefly survey the many experiments which have measured the anisotropies
of the CMB and led to crucial advances in observational Cosmology. The somewhat
frantic series of new results has recently culminated with the outcome of the
WMAP satellite which confirmed earlier results, set new standards of accuracy,
and suggested that the Universe may have reionised earlier than anticipated.
Many more CMB experiments are currently taking data or being planned, with the
Planck satellite on the 2007 Horizon poised to extract all the cosmological
information in the temperature anisotropies, and foray deeply into
polarisation.Comment: To appear in the proceedings of "Where Cosmology and Fundamental
Physics Meet", 23-26 June, 2003, Marseille, Franc
Large scale CMB anomalies from thawing cosmic strings
Cosmic strings formed during inflation are expected to be either diluted over
super-Hubble distances, i.e., invisible today, or to have crossed our past
light cone very recently. We discuss the latter situation in which a few
strings imprint their signature in the Cosmic Microwave Background (CMB)
Anisotropies after recombination. Being almost frozen in the Hubble flow, these
strings are quasi static and evade almost all of the previously derived
constraints on their tension while being able to source large scale
anisotropies in the CMB sky. Using a local variance estimator on thousand of
numerically simulated Nambu-Goto all sky maps, we compute the expected signal
and show that it can mimic a dipole modulation at large angular scales while
being negligible at small angles. Interestingly, such a scenario generically
produces one cold spot from the thawing of a cosmic string loop. Mixed with
anisotropies of inflationary origin, we find that a few strings of tension GU =
O(1) x 10^(-6) match the amplitude of the dipole modulation reported in the
Planck satellite measurements and could be at the origin of other large scale
anomalies.Comment: 23 pages, 11 figures, uses jcappub. References added, matches
published versio
The Structure and Dynamical Evolution of Dark Matter Halos
(Shortened) We use N-body simulations to investigate the structure and
dynamical evolution of dark matter halos in galaxy clusters. Our sample
consists of nine massive halos from an EdS universe with scale free power
spectrum and n = -1. Halos are resolved by ~20000 particles each, with a
dynamical resolution of 20-25 kpc. Large scale tidal fields are included up to
L=150 Mpc using background particles. The halo formation process can be
characterized by the alternation of two dynamical configurations: a merging
phase and a relaxation phase, defined by their signature on the evolution of
the total mass and rms velocity. Halos spend on average one 1/3 of their
evolution in the merging phase and 2/3 in the relaxation phase. Using this
definition, we study the density profiles and their change during the halo
history. The average density profiles are fitted by the NFW analytical model
with an rms residual of 17% between the virial radius Rv and 0.01 Rv. The
Hernquist (1990) profiles fits the same halos with an rms residual of 26%. The
trend with mass of the scale radius of these fits is marginally consistent with
that found by Cole & Lacey (1996): in comparison our halos are more centrally
concentrated, and the relation between scale radius and halo mass is slightly
steeper. We find a moderately large scatter in this relation, due both to
dynamical evolution within halos and to fluctuations in the halo population. We
analyze the dynamical equilibrium of our halos using the Jeans' equation, and
find that on average they are approximately in equilibrium within their virial
radius. Finally, we find that the projected mass profiles of our simulated
halos are in very good agreement with the profiles of three rich galaxy
clusters derived from strong and weak gravitational lensing observations.Comment: 20 pages, Latex, with all figures included. Modified to match the
published versio
Previrialization: Perturbative and N-Body Results
We present a series of N-body experiments which confirm the reality of the
previrialization effect. We also use weakly nonlinear perturbative approach to
study the phenomenon. These two approaches agree when the rms density contrast,
, is small; more surprisingly, they remain in agreement when . When the slope of the initial power spectrum is , nonlinear
tidal interactions slow down the growth of density fluctuations and the
magnitude of the suppression increases when (i.e. the relative amount of
small scale power) is increased. For we see an opposite effect: the
fluctuations grow more rapidly than in linear theory. The transition occurs at
when the weakly nonlinear correction to is close to zero and
the growth rate is close to linear. Our results resolve recent controversy
between two N-body studies of previrialization. Peebles (1990) assumed
and found strong evidence in support of previrialization, while Evrard \& Crone
(1992), who assumed , reached opposite conclusions. As we show here, the
initial conditions with are rather special because the nonlinear effects
nearly cancel out for that particular spectrum. In addition to our calculations
for scale-free initial spectra, we show results for a more realistic spectrum
of Peacock \& Dodds (1994). Its slope near the scale usually adopted for
normalization is close to , so is close to linear. Our results
retroactively justify linear normalization at 8 Mpc, while also
demonstrating the danger and limitations of this practice.Comment: Significantly revised, 25 pages, uuencoded compressed postscript,
figures included, to appear in Ap
Probing CMB Non-Gaussianity Using Local Curvature
It is possible to classify pixels of a smoothed cosmic microwave background
(CMB) fluctuation map according to their local curvature in ``hill'', ``lake''
and ``saddle'' regions. In the Gaussian case, fractional areas occupied by
pixels of each kind can be computed analytically for families of excursion sets
as functions of threshold and moments of the fluctuation power spectrum. We
show how the shape of these functions can be used to constrain accurately the
level of non-Gaussianity in the data by applying these new statistics to an
hypothetical mixed model suggested by Bouchet et al. (2001). According to our
simple test, with only one 12.5x12.5 deg^2 map, Planck should be able to detect
with a high significance a non-Gaussian level as weak as 10% in temperature
standard deviation (rms) (5% in C_l), whereas a marginal detection would be
possible for MAP with a non-Gaussian level around 30% in temperature (15% in
C_l).Comment: 11 pages, 13 figures, submitted to MNRA
Moments of the Counts Distribution in the 1.2 Jy IRAS Redshift Survey
We derive the volume-averaged 2, 3, 4, and 5-point correlation functions from
the moments of the Count probability distribution function of a redshift survey
of IRAS galaxies, and find them all to be reasonably well-described by power
laws. Weak systematic effects with the sample size provide evidence for
stronger clustering of galaxies of higher luminosity on small scales.
Nevertheless, remarkably tight relationships hold between the correlation
functions of different order. In particular, the ``normalized" skewness defined
by the ratio varies at most weakly with
scale in the range . That is, is close to
constant () from weakly to strongly non-linear scales.
Furthermore, we find that the void probability function obeys a scaling
relation with density to great precision, in accord with the scale-invariance
hypothesis ().Comment: 38 pages, postscript file (1.3 Megabytes) . IAS preprint number AST
93/2
A consensus genetic map of sorghum that integrates multiple component maps and high-throughput Diversity Array Technology (DArT) markers
Background: Sorghum genome mapping based on DNA markers began in the early 1990s and numerous genetic linkage maps of sorghum have been published in the last decade, based initially on RFLP markers with more recent maps including AFLPs and SSRs and very recently, Diversity Array Technology (DArT) markers. It is essential to integrate the rapidly growing body of genetic linkage data produced through DArT with the multiple genetic linkage maps for sorghum generated through other marker technologies. Here, we report on the colinearity of six independent sorghum component maps and on the integration of these component maps into a single reference resource that contains commonly utilized SSRs, AFLPs, and high-throughput DArT markers
The Spitzer Survey of the Small Magellanic Cloud: S3MC Imaging and Photometry in the Mid- and Far-Infrared Wavebands
We present the initial results from the Spitzer Survey of the Small
Magellanic Cloud (S3MC), which imaged the star-forming body of the Small
Magellanic Cloud (SMC) in all seven MIPS and IRAC wavebands. We find that the
F_8/F_24 ratio (an estimate of PAH abundance) has large spatial variations and
takes a wide range of values that are unrelated to metallicity but
anticorrelated with 24 um brightness and F_24/F_70 ratio. This suggests that
photodestruction is primarily responsible for the low abundance of PAHs
observed in star-forming low-metallicity galaxies. We use the S3MC images to
compile a photometric catalog of ~400,000 mid- and far-infrared point sources
in the SMC. The sources detected at the longest wavelengths fall into four main
categories: 1) bright 5.8 um sources with very faint optical counterparts and
very red mid-infrared colors ([5.8]-[8.0]>1.2), which we identify as YSOs. 2)
Bright mid-infrared sources with mildly red colors (0.16<[5.8]-[8.0]<0.6),
identified as carbon stars. 3) Bright mid-infrared sources with neutral colors
and bright optical counterparts, corresponding to oxygen-rich evolved stars.
And, 4) unreddened early B stars (B3 to O9) with a large 24 um excess. This
excess is reminiscent of debris disks, and is detected in only a small fraction
of these stars (<5%). The majority of the brightest infrared point sources in
the SMC fall into groups one to three. We use this photometric information to
produce a catalog of 282 bright YSOs in the SMC with a very low level of
contamination (~7%).Comment: Accepted for publication in The Astrophysical Journal. Given the
draconian figure file-size limits implemented in astro-ph, readers are
encouraged to download the manuscript with full quality images from
http://celestial.berkeley.edu/spitzer/publications/s3mcsurvey.pd