479 research outputs found
Probing the primordial Universe with MeerKAT and DES
It is usually assumed that we will need to wait until next-generation surveys
like Euclid, LSST and SKA, in order to improve on the current best constraints
on primordial non-Gaussianity from the Planck experiment. We show that two
contemporary surveys, with the SKA precursor MeerKAT and the Dark Energy Survey
(DES), can be combined using the multi-tracer technique to deliver an accuracy
on measurement of that is up to three times better than Planck.Comment: 7 pages, 5 figures, 1 table. We now marginalise over the bias, and
ensure that we exclude nonlinear scales, leading to small quantitative
corrections. Version accepted by MNRA
Cosmology with intensity mapping techniques using atomic and molecular lines
We present a systematic study of the intensity mapping technique using
updated models for the different emission lines from galaxies and identify
which ones are more promising for cosmological studies of the post reionization
epoch. We consider the emission of , , H,
optical and infrared oxygen lines, nitrogen lines, CII and the CO rotational
lines. We then identify that , , OII, CII and
the lowest rotational CO lines are the best candidates to be used as IM probes.
These lines form a complementary set of probes of the galaxies emission
spectra. We then use reasonable experimental setups from current, planned or
proposed experiments to access the detectability of the power spectrum of each
emission line. Intensity mapping of emission from to 3
will be possible in the near future with HETDEX, while far-infrared lines
require new dedicated experiments. We also show that the proposed SPHEREx
satellite can use OII and IM to study the large-scale
distribution of matter in intermediate redshifts of 1 to 4. We found that
submilimeter experiments with bolometers can have similar performances at
intermediate redshifts using CII and CO(3-2).Comment: 18 pages, 21 figures, 5 tables, published in MNRAS, typos correcte
Cosmic Reionization and the 21-cm signal: Comparison between an analytical model and a simulation
We measure several properties of the reionization process and the
corresponding low-frequency 21-cm signal associated with the neutral hydrogen
distribution, using a large volume, high resolution simulation of cosmic
reionization. The brightness temperature of the 21-cm signal is derived by
post-processing this numerical simulation with a semi-analytical prescription.
Our study extends to high redshifts (z ~ 25) where, in addition to collisional
coupling, our post-processed simulations take into account the inhomogeneities
in the heating of the neutral gas by X-rays and the effect of an inhomogeneous
Lya radiation field. Unlike the well-studied case where spin temperature is
assumed to be significantly greater than the temperature of the cosmic
microwave background due to uniform heating of the gas by X-rays, spatial
fluctuations in both the Lya radiation field and X-ray intensity impact
predictions related to the brightness temperature at z > 10, during the early
stages of reionization and gas heating. The statistics of the 21-cm signal from
our simulation are then compared to existing analytical models in the
literature and we find that these analytical models provide a reasonably
accurate description of the 21-cm power spectrum at z < 10. Such an agreement
is useful since analytical models are better suited to quickly explore the full
astrophysical and cosmological parameter space relevant for future 21-cm
surveys. We find, nevertheless, non-negligible differences that can be
attributed to differences in the inhomogeneous X-ray heating and Lya coupling
at z > 10 and, with upcoming interferometric data, these differences in return
can provide a way to better understand the astrophysical processes during
reionization.Comment: Major paper revision to match version accepted for publication in
ApJ. Simulation now fully includes fluctuations in the X-ray heating and the
Lya radiation field. 18 pages, 13 figure
Avaliação estrutural do aço rápido M3/2 sinterizado através da tecnologia DMLS
O estudo da sinterização do pó de aço rápido M3/2 pela tecnologia DMLS baseou-se na utilização de diferentes parâmetros de processo e na optimização da respectiva distribuição granulométrica e densidade aparente. O material foi sinterizado em linha, área e volume utilizando uma distância entre linhas de varrimento constante (0.30mm), três velocidades de varrimento do laser (50, 150, 250mm/s) e duas potências de laser (154 and 180W). O aço rápido M3/2 foi utilizado tal qual e com diferentes adições de uma fracção fina do mesmo material de modo a aumentar a densidade aparente
Optimised angular power spectra for spectroscopic galaxy surveys
The angular power spectrum is a gauge-independent observable that is in
principle the natural tool for analysing galaxy number counts. In practice, the
problem is that the computational requirements for next-generation
spectroscopic surveys such as Euclid and the Square Kilometre Array are
currently unfeasible. We propose a new method to save computational time for
spectroscopic angular power spectra. This hybrid method is modelled on the
Fourier power spectrum approach of treating relatively thick redshift bins
(redshift width ~0.1) as separate surveys. In the hybrid method, each thick bin
is further subdivided into thin bins (redshift width ~0.01); all the
correlations within each thick bin are computed, while cross-bin correlations
beyond the thick bins are neglected. Constraints on cosmological parameters
from the hybrid method are comparable to those from the standard galaxy power
spectrum analysis - but they have the advantage that cosmic evolution,
wide-angle and lensing effects are naturally included, while no
Alcock-Paczynski correction is needed. The hybrid method delivers much tighter
constraints than a 2D tomographic approach that is typical for photometric
surveys, which considers only thick bins and the correlations between them.
Furthermore, for standard cosmological parameters our method is not biased by
neglecting the effects of lensing on number counts, while the tomographic
method is strongly biased.Comment: 11 pages, 7 figures, 4 tables. Typo in Eq. (2) fixe
Prospects for detecting CII emission during the Epoch of Reionization
We produce simulations of emission of the atomic CII line in large sky fields
in order to determine the current prospects for mapping this line during the
high redshift Epoch of Reionization. We estimate the CII line intensity,
redshift evolution and spatial fluctuations using observational relations
between CII emission and the SFR in a galaxy for the frequency range of 200 GHz
to 300 GHz. We obtained a frequency averaged intensity of CII emission of in the redshift range
. Observations of CII emission in this frequency
range will suffer contamination from emission lines at lower redshifts, in
particular from the CO rotation lines. For the relevant frequency range we
estimated the CO contamination (originated in emission from galaxies at ), using simulations, to be and independently confirmed the result based in observational
relations. We generated maps as a function of angle and frequency using
detailed simulations of the CII and CO emission across several redshifts in
order to properly take into account the observational pipeline and light cone
effects. In order to reduce the foreground contamination we found that we
should mask galaxies below redshifts with a CO flux in one of the
CO(J:2-1) to CO(J:6-5) lines higher than
or a AB magnitude lower than . We estimate that the
additional continuum contamination is of the order of . It is also considered the possibility of cross correlating
foreground lines with galaxies in order to probe the intensity of the
foregrounds.Comment: 19 pages, 14 figure
Photonic superdiffusive motion in resonance radiation trapping
In this work we consider the relation between the jump length probability density function and the
line shape function in resonance radiation trapping in atomic vapors. The two-sided jump length
probability density function suitable for a unidimensional formulation of radiative transfer is also derived. As a side result, a procedure to obtain the Maxwell distribution of velocities from the Maxwell-Boltzmann distribution of speeds was obtained. General relations that give the asymptotic
jump length behavior and the Lévy flight parameter niu for any line shape are obtained. The results
are applied to generalized Doppler, generalized Lorentz, and Voigt line shape functions. It is
concluded that the lighter the tail of the line shape function, the less heavy the tail of the jump length
probability density function, although this tail is always heavy, with niu <= 1
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