155 research outputs found
Optimization of spectroscopic surveys for testing non-Gaussianity
We investigate optimization strategies to measure primordial non-Gaussianity
with future spectroscopic surveys. We forecast measurements coming from the 3D
galaxy power spectrum and compute constraints on primordial non-Gaussianity
parameters f_NL and n_NG. After studying the dependence on those parameters
upon survey specifications such as redshift range, area, number density, we
assume a reference mock survey and investigate the trade-off between number
density and area surveyed. We then define the observational requirements to
reach the detection of f_NL of order 1. Our results show that while power
spectrum constraints on non-Gaussianity from future spectroscopic surveys can
be competitive with current CMB limits, measurements from higher-order
statistics will be needed to reach a sub unity precision in the measurements of
the non-Gaussianity parameter f_NL.Comment: 12 pages, 10 figure
Interloper bias in future large-scale structure surveys
Next-generation spectroscopic surveys will map the large-scale structure of
the observable universe, using emission line galaxies as tracers. While each
survey will map the sky with a specific emission line, interloping emission
lines can masquerade as the survey's intended emission line at different
redshifts. Interloping lines from galaxies that are not removed can contaminate
the power spectrum measurement, mixing correlations from various redshifts and
diluting the true signal. We assess the potential for power spectrum
contamination, finding that an interloper fraction worse than 0.2% could bias
power spectrum measurements for future surveys by more than 10% of statistical
errors, while also biasing power spectrum inferences. We also construct a
formalism for predicting cosmological parameter bias, demonstrating that a
0.15%-0.3% interloper fraction could bias the growth rate by more than 10% of
the error, which can affect constraints on gravity upcoming surveys. We use the
COSMOS Mock Catalog (CMC), with the emission lines re-scaled to better
reproduce recent data, to predict potential interloper fractions for the Prime
Focus Spectrograph (PFS) and the Wide-Field InfraRed Survey Telescope (WFIRST).
We find that secondary line identification, or confirming galaxy redshifts by
finding correlated emission lines, can remove interlopers for PFS. For WFIRST,
we use the CMC to predict that the 0.2% target can be reached for the WFIRST
H survey, but sensitive optical and near-infrared photometry will be
required. For the WFIRST [OIII] survey, the predicted interloper fractions
reach several percent and their effects will have to be estimated and removed
statistically (e.g. with deep training samples). (Abridged)Comment: Matches version accepted by PAS
Freezing Out Early Dark Energy
A phenomenological model of dark energy that tracks the baryonic and cold
dark matter at early times but resembles a cosmological constant at late times
is explored. In the transition between these two regimes, the dark energy
density drops rapidly as if it were a relic species that freezes out, during
which time the equation of state peaks at +1. Such an adjustment in the dark
energy density, as it shifts from scaling to potential-domination, could be the
signature of a trigger mechanism that helps explain the late-time cosmic
acceleration. We show that the non-negligible dark energy density at early
times, and the subsequent peak in the equation of state at the transition,
leave an imprint on the cosmic microwave background anisotropy pattern and the
rate of growth of large scale structure. The model introduces two new
parameters, consisting of the present-day equation of state and the redshift of
the freeze-out transition. A Monte Carlo Markov Chain analysis of a
ten-dimensional parameter space is performed to compare the model with
pre-Planck cosmic microwave background, large scale structure and supernova
data and measurements of the Hubble constant. We find that the transition
described by this model could have taken place as late as a redshift z~400. We
explore the capability of future cosmic microwave background and weak lensing
experiments to put tighter constraints on this model. The viability of this
model may suggest new directions in dark-energy model building that address the
coincidence problem.Comment: 11 pages, 15 figure
Measuring with the SPHEREx Multi-tracer Redshift Space Bispectrum
The bispectrum is an important statistics helpful for measuring the
primordial non-Gaussianity parameter to less than order unity
in error, which would allow us to distinguish between single and multi-field
inflation models. The Spectro-Photometer for the History of the Universe, Epoch
of Reionization and Ices Explorer (SPHEREx) mission is particularly well-suited
for making this measurement with its 100-band all-sky observations in the
near-infrared. Consequently, the SPHEREx data will contain galaxies with
spectroscopic-like redshift measurements as well as those with much larger
errors. In this paper, we evaluate the impact of photometric redshift errors on
constraints in the context of an updated multi-tracer
forecast for SPHEREx, finding that the azimuthal averages of the first three
even bispectrum multipoles are no longer sufficient for capturing most of the
information (as opposed to the case of spectroscopic surveys shown in the
literature). The final SPHEREx result with all five galaxy samples and six
redshift bins is however not severely impacted because the total result is
dominated by the samples with the best redshift errors, while the worse samples
serve to reduce cosmic variance. Our fiducial result of
from bispectrum alone is increased by
and when using and 2 respectively. We also explore
the impact on parameter constraints when varying the fiducial redshift errors,
as well as using subsets of multi-tracer combinations or triangles with
different squeezing factors. Note that the fiducial result here is not the
final SPHEREx capability, which is still on target for being
once the power spectrum will be included.Comment: 15 pages, 3 figure
Investigation of the release of particles from a nanocoated product
International audienceManufactured products are being coated with nanoparticles in order to functionalize them with antibacterial or self-cleaning properties or to improve their durability etc. As the (eco-) toxicological effects of the nanoparticles are not well known yet, their use could lead to new potential risks for the workers, the consumers and the environment. This study focuses on the release of the nanoparticles during the operations related to the handling and processing of an automotive part. The part is made up of a metallic alloy and, in order to reduce friction, the part is nano-coated with inorganic fullerenes. The mechanical stresses appearing during these operations are reproduced in a nano-secured facility. The release of nanoparticles is found to be increasing with the wear energy applied on the surface
- …