202 research outputs found
Precision era of the kinetic Sunyaev-Zeldovich effect: simulations, analytical models and observations and the power to constrain reionization
The kinetic SZ effect, which is the dominant CMB source at arc-minute scales
and Ghz, probes the ionized gas peculiar momentum up to the
epoch of reionization and is a sensitive measure of the reionization history.
We ran high resolution self-similar and CDM hydro simulations and
built an analytical model to study this effect. Our model reproduces the
CDM simulation results to several percent accuracy, passes various
tests against self-similar simulations, and shows a wider range of
applicability than previous analytical models. Our model in its continuous
version is free of simulation limitations such as finite simulation box and
finite resolution and allows an accurate prediction of the kinetic SZ power
spectrum . For the WMAP cosmology, we find for the reionization redshift and
. The corresponding temperature fluctuation is several K at
these ranges. The dependence of on the reionization history allows an
accurate measurement of the reionization epoch. For the Atacama cosmology
telescope experiment, can be measured with accuracy.
scales as . Given cosmological parameters,
ACT would be able to constrain with several percent accuracy.
Some multi-reionization scenarios degenerate in the primary CMB temperature and
TE measurement can be distinguished with confidence.Comment: 14 pages, 7 figures. Accepted by MNRAS. We corrected the primary CMB
power spectrum we used. We added discussions about the effects of lensing and
relativistic SZ correctio. We withdraw a claim about the patchy reionizatio
Risk of Arrhythmia and Mortality from Macrolide Antibiotic Prescription: A Population-Based Cohort Study
Many respiratory tract infections are treated with macrolide antibiotics. Regulatory agencies warn that these antibiotics increase the risk of ventricular arrhythmia. This population-based retrospective cohort study examined the 30-day risk of a hospital encounter with ventricular arrhythmia and all-cause mortality in 503,612 matched pairs of older adults who received a new outpatient prescription for an oral macrolide antibiotic and those prescribed referent antibiotics from 2002 to 2013 in Ontario. Conditional logistic regression was used to measure the association between macrolide exposure and outcomes. Macrolide antibiotics compared with referent antibiotics were not associated with a higher 30-day risk of ventricular arrhythmia (0.03% vs. 0.03%, relative risk [RR] 1.06, 95% confidence interval [CI] 0.83- 1.36), and were associated with a lower risk of 30-day all-cause mortality (0.62% vs. 0.76%, RR 0.82, 95% CI 0.78-0.86). These findings suggest that current warnings from Health Canada and the U.S. Food and Drug Administration may be overstated
Optimized Multi-Frequency Spectra for Applications in Radiative Feedback and Cosmological Reionization
The recent implementation of radiative transfer algorithms in numerous
hydrodynamics codes has led to a dramatic improvement in studies of feedback in
various astrophysical environments. However, because of methodological
limitations and computational expense, the spectra of radiation sources are
generally sampled at only a few evenly-spaced discrete emission frequencies.
Using one-dimensional radiative transfer calculations, we investigate the
discrepancies in gas properties surrounding model stars and accreting black
holes that arise solely due to spectral discretization. We find that even in
the idealized case of a static and uniform density field, commonly used
discretization schemes induce errors in the neutral fraction and temperature by
factors of two to three on average, and by over an order of magnitude in
certain column density regimes. The consequences are most severe for radiative
feedback operating on large scales, dense clumps of gas, and media consisting
of multiple chemical species. We have developed a method for optimally
constructing discrete spectra, and show that for two test cases of interest,
carefully chosen four-bin spectra can eliminate errors associated with
frequency resolution to high precision. Applying these findings to a fully
three-dimensional radiation-hydrodynamic simulation of the early universe, we
find that the HII region around a primordial star is substantially altered in
both size and morphology, corroborating the one-dimensional prediction that
discrete spectral energy distributions can lead to sizable inaccuracies in the
physical properties of a medium, and as a result, the subsequent evolution and
observable signatures of objects embedded within it.Comment: 15 pages, 13 figures, 2 tables, accepted for publication in the
Astrophysical Journa
Dynamical Mass Measurements of Contaminated Galaxy Clusters Using Machine Learning
We study dynamical mass measurements of galaxy clusters contaminated by
interlopers and show that a modern machine learning (ML) algorithm can predict
masses by better than a factor of two compared to a standard scaling relation
approach. We create two mock catalogs from Multidark's publicly available
-body MDPL1 simulation, one with perfect galaxy cluster membership
information and the other where a simple cylindrical cut around the cluster
center allows interlopers to contaminate the clusters. In the standard
approach, we use a power-law scaling relation to infer cluster mass from galaxy
line-of-sight (LOS) velocity dispersion. Assuming perfect membership knowledge,
this unrealistic case produces a wide fractional mass error distribution, with
a width of . Interlopers introduce additional
scatter, significantly widening the error distribution further
(). We employ the support distribution machine (SDM)
class of algorithms to learn from distributions of data to predict single
values. Applied to distributions of galaxy observables such as LOS velocity and
projected distance from the cluster center, SDM yields better than a
factor-of-two improvement () for the contaminated
case. Remarkably, SDM applied to contaminated clusters is better able to
recover masses than even the scaling relation approach applied to
uncontaminated clusters. We show that the SDM method more accurately reproduces
the cluster mass function, making it a valuable tool for employing cluster
observations to evaluate cosmological models.Comment: 18 pages, 12 figures, accepted for publication at Ap
Radiative transfer simulations of cosmic reionization I: methodology and initial results
We present a new hybrid code for large volume, high resolution simulations of
cosmic reionization, which utilizes a N-body algorithm for dark matter,
physically motivated prescriptions for baryons and star formation, and an
adaptive ray tracing algorithm for radiative transfer of ionizing photons. Two
test simulations each with 3 billion particles and 400 million rays in a 50
Mpc/h box have been run to give initial results. Halos are resolved down to
virial temperatures of 10^4 K for the redshift range of interest in order to
robustly model star formation and clumping factors. This is essential to
correctly account for ionization and recombination processes. We find that the
halos and sources are strongly biased with respect to the underlying dark
matter, re-enforcing the requirement of large simulation boxes to minimize
cosmic variance and to obtain a qualitatively correct picture of reionization.
We model the stellar initial mass function (IMF), by following the spatially
dependent gas metallicity evolution, and distinguish between the first
generation, Population III (PopIII) stars and the second generation, Population
II (PopII) stars. The PopIII stars with a top-heavy IMF produce an order of
magnitude more ionizing photons at high redshifts z>10, resulting in a more
extended reionization. In our simulations, complete overlap of HII regions
occurrs at z~6.5 and the computed mass and volume weighted residual HI
fractions at 5<z<6.5 are both in good agreement with high redshift quasar
absorption measurements from SDSS. The values for the Thomson optical depth are
consistent within 1-sigma of the current best-fit value from third-year WMAP.Comment: 15 pages, 13 figures; accepted by ApJ; higher resolution figures can
be found at http://www.astro.princeton.edu/~htrac/reionization.htm
- …