381 research outputs found
Gaussianizing the non-Gaussian lensing convergence field I: the performance of the Gaussianization
Motivated by recent works of Neyrinck et al. 2009 and Scherrer et al. 2010,
we proposed a Gaussianization transform to Gaussianize the non-Gaussian lensing
convergence field . It performs a local monotonic transformation
pixel by pixel to make the unsmoothed one-point
probability distribution function of the new variable Gaussian. We tested
whether the whole field is Gaussian against N-body simulations. (1) We
found that the proposed Gaussianization suppresses the non-Gaussianity by
orders of magnitude, in measures of the skewness, the kurtosis, the 5th- and
6th-order cumulants of the field smoothed over various angular scales
relative to that of the corresponding smoothed field. The residual
non-Gaussianities are often consistent with zero within the statistical errors.
(2) The Gaussianization significantly suppresses the bispectrum. Furthermore,
the residual scatters around zero, depending on the configuration in the
Fourier space. (3) The Gaussianization works with even better performance for
the 2D fields of the matter density projected over \sim 300 \mpch distance
interval centered at , which can be reconstructed from the weak
lensing tomography. (4) We identified imperfectness and complexities of the
proposed Gaussianization. We noticed weak residual non-Gaussianity in the
field. We verified the widely used logarithmic transformation as a good
approximation to the Gaussianization transformation. However, we also found
noticeable deviations.Comment: 13 pages, 15 figures, accepted by PR
Gaussianizing the non-Gaussian lensing convergence field II: the applicability to noisy data
In paper I (Yu et al. [1]), we show through N-body simulation that a local
monotonic Gaussian transformation can significantly reduce non-Gaussianity in a
noise-free lensing convergence field. This makes the Gaussianization a
promising theoretical tool to understand high-order lensing statistics. Here we
present a study of its applicability in lensing data analysis, in particular
when shape measurement noise is presented in lensing convergence maps. (i) We
find that shape measurement noise significantly degrades the Gaussianization
performance and the degradation increases for shallower surveys. (ii) The
Wiener filter is efficient in reducing the impact of shape measurement noise.
The Gaussianization of the Wiener-filtered lensing maps is able to suppress
skewness, kurtosis, and the 5th- and 6th-order cumulants by a factor of 10 or
more. It also works efficiently to reduce the bispectrum to zero.Comment: 13 pages, 10 figures. Match the published version. Accepted by PR
An estimate of \Omega_m without priors
Using mean relative peculiar velocity measurements for pairs of galaxies, we
estimate the cosmological density parameter and the amplitude of
density fluctuations . Our results suggest that our statistic is a
robust and reproducible measure of the mean pairwise velocity and thereby the
parameter. We get and . These estimates do not depend on prior assumptions on
the adiabaticity of the initial density fluctuations, the ionization history,
or the values of other cosmological parameters.Comment: 12 pages, 4 figures, slight changes to reflect published versio
Protecting the Primordial Baryon Asymmetry From Erasure by Sphalerons
If the baryon asymmetry of the universe was created at the GUT scale,
sphalerons together with exotic sources of -violation could have erased
it, unless the latter satisfy stringent bounds. We elaborate on how the small
Yukawa coupling of the electron drastically weakens previous estimates of these
bounds.Comment: 41 pp., 4 latex figures included and 3 uuencoded or postscript
figures available by request, UMN-TH-1213-9
Manipulating Environmental Clutter Reveals Dynamic Active Sensing Strategies in Big Brown Bats
Vocalizing animals confront acoustically challenging conditions in which background noise (clutter) can mask or shift attention away from biologically relevant signals. Echolocating big brown bats (Eptesicus fuscus) are excellent comparative models for studying how animals differentiate between multiple sound sources in complex acoustic scenes. We trained four big brown bats to fly down an asymmetrical corridor producing distinct clutter echoes from the two sides. While in flight, they were presented with playbacks of exemplars of an echolocation call, a social communication call, or waterfall noise, from one or both sides of this corridor; a silence condition served as a control. We predicted that bats would perceive the playbacks, as indexed by modifications of their vocalizations and shifts in their head aim. Bats completed flights at a high rate of success in all conditions. Although bats produced calls in similar sized sonar sound groups in playback and silent trials, they emitted more echolocation calls and shortened the time intervals between calls in response to playbacks. These comparisons suggest the playbacks increased the perceptual difficulty of the task to some extent. Bats aimed their heads towards the left side of the corridor where clutter echoes were acoustically stronger but also sparser. Changes in head aim in response to playbacks were small. Our data suggest that big brown bats flying through clutter detect differences in the information content of surrounding acoustic scenes and alter their echolocation behavior accordingly
Formation of Highly Oxidized Molecules from NO3 Radical Initiated Oxidation of Delta-3-Carene : A Mechanistic Study
NO3 radical oxidation of most monoterpenes is a significant source of secondary organic aerosol (SOA) in many regions influenced by both biogenic and anthropogenic emissions, but there are very few published mechanistic studies of NO3 chemistry beyond simple first generation products. Here, we present a computationally derived mechanism detailing the unimolecular pathways available to the second generation of peroxy radicals following NO3 oxidation of Delta-3-carene, defining generations based on the sequence of peroxy radicals formed rather than number of oxidant attacks. We assess five different types of unimolecular reactions, including peroxy and alkoxy radical (RO2 and RO) hydrogen shifts, RO2 and RO ring closing (e.g., endoperoxide formation), and RO decomposition. Rate constants calculated using quantum chemical methods indicate that this chemical system has significant contribution from both bimolecular and unimolecular pathways. The dominant unimolecular reactions are endoperoxide formation, RO H-shifts, and RO decomposition. However, the complexity of the overall reaction is tempered as only 1 or 2 radical propagation pathways dominate the fate of each radical intermediate. Chemical ionization mass spectrometry (CIMS) measurements using the NO3- reagent ion during Delta-3-carene + NO3 chamber experiments show products consistent with each of the three types of unimolecular reactions predicted to be important from the computational mechanism. Moreover, the SIMPOL group contribution method for predicting vapor pressures suggests that a majority of the closed-shell products inferred from these unimolecular reactions are likely to have low enough vapor pressure to be able to contribute to SOA formation.Peer reviewe
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The XMM-Newton Wide field survey in the COSMOS field: redshift evolution of AGN bias and subdominant role of mergers in triggering moderate luminosity AGN at redshift up to 2.2
We present a study of the redshift evolution of the projected correlation
function of 593 X-ray selected AGN with I_AB<23 and spectroscopic redshifts
z<4, extracted from the 0.5-2 keV X-ray mosaic of the 2.13 deg^2 XMM-COSMOS
survey. We introduce a method to estimate the average bias of the AGN sample
and the mass of AGN hosting halos, solving the sample variance using the halo
model and taking into account the growth of the structure over time. We find
evidence of a redshift evolution of the bias factor for the total population of
XMM-COSMOS AGN from b(z=0.92)=2.30 +/- 0.11 to b(z=1.94)=4.37 +/- 0.27 with an
average mass of the hosting DM halos logM [h^-1 M_sun] ~ 13.12 +/- 0.12 that
remains constant at all z < 2. Splitting our sample into broad optical lines
AGN (BL), AGN without broad optical lines (NL) and X-ray unobscured and
obscured AGN, we observe an increase of the bias with redshift in the range
z=0.7-2.25 and z=0.6-1.5 which corresponds to a constant halo mass logM [h^-1
M_sun] ~ 13.28 +/- 0.07 and logM [h^-1 M_sun] ~ 13.00 +/- 0.06 for BL /X-ray
unobscured AGN and NL/X-ray obscured AGN, respectively. The theoretical models
which assume a quasar phase triggered by major mergers can not reproduce the
high bias factors and DM halo masses found for X-ray selected BL AGN with L_BOL
~ 2e45 erg s^-1. Our work extends up to z ~ 2.2 the z <= 1 statement that, for
moderate luminosity X-ray selected BL AGN, the contribution from major mergers
is outnumbered by other processes, possibly secular such as tidal disruptions
or disk instabilities.Comment: 16 emulateapj pages, 18 figures and 3 tables. Accepted for the
publication in The Astrophysical Journa
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