262 research outputs found
Constraining the Collisional Nature of the Dark Matter Through Observations of Gravitational Wakes
We propose to use gravitational wakes as a direct observational probe of the
collisional nature of the dark matter. We calculate analytically the structure
of a wake generated by the motion of a galaxy in the core of an X-ray cluster
for dark matter in the highly-collisional and collisionless limits. We show
that the difference between these limits can be recovered from detailed X-ray
or weak lensing observations. We also discuss the sizes of sub-halos in these
limits. Preliminary X-ray data on the motion of NGC 1404 through the Fornax
group disfavors fluid-like dark matter but does not exclude scenarios in which
the dark matter is weakly collisional.Comment: 29 pages, 3 figures, submitted to Ap
Searching for the earliest galaxies in the 21 cm forest
We use a model developed by Xu et al. (2010) to compute the 21 cm line
absorption signatures imprinted by star-forming dwarf galaxies (DGs) and
starless minihalos (MHs). The method, based on a statistical comparison of the
equivalent width (W_\nu) distribution and flux correlation function, allows us
to derive a simple selection criteria for candidate DGs at very high (z >= 8)
redshift. We find that ~ 18% of the total number of DGs along a line of sight
to a target radio source (GRB or quasar) can be identified by the condition
W_\nu < 0; these objects correspond to the high-mass tail of the DG
distribution at high redshift, and are embedded in large HII regions. The
criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs
could later be re-observed in the near-IR by the JWST with high efficiency,
thus providing a direct probe of the most likely reionization sources.Comment: 8 pages, 3 figures. Accepted for publication in Science in China
Series
Reionization: Characteristic Scales, Topology and Observability
Recently the numerical simulations of the process of reionization of the
universe at z>6 have made a qualitative leap forward, reaching sufficient sizes
and dynamic range to determine the characteristic scales of this process. This
allowed making the first realistic predictions for a variety of observational
signatures. We discuss recent results from large-scale radiative transfer and
structure formation simulations on the observability of high-redshift Ly-alpha
sources. We also briefly discuss the dependence of the characteristic scales
and topology of the ionized and neutral patches on the reionization parameters.Comment: 4 pages, 5 figures (4 in color), to appear in Astronomy and Space
Science special issue "Space Astronomy: The UV window to the Universe",
proceedings of 1st NUVA Conference ``Space Astronomy: The UV window to the
Universe'' in El Escorial (Spain
HIPERTENSÃO, HIPERTERNIA, TOSSE PRODUTIVA
Dr. Luís Felipe Mallmann – (Residente do Serviço de Medicina Interna- HCPA/UFRGS): Uma mulher branca de 67 anos veio à Emergência do HCPA no dia 24/02/2002 com queixa de dor nas costas contínua, com início há aproximadamente 18 h, acompanhada de febre, calafrios e tosse com expectoração esbranquiçada. Relatava ter tido febre e ser portadora de hipertensão arterial sistêmica (HAS), sem tratamento, e uso de fumo. O exame físico mostrou estado geral regular, sensório deprimido, TA= 130/80 mmHg, temperatura axilar= 36,2 o C e saturação de 02 = 95%, em ar ambiente. A ausculta pulmonar mostrou murmúrio vesicular uniformemente diminuído, roncos difusos e estertores crepitantes na base direita. A punhopercussão lombar foi dolorosa à direita. Os exames laboratoriais estão descritos nas tabelas 1, 2 e 3.Dr. Luís Felipe Mallmann – (Residente do Serviço de Medicina Interna- HCPA/UFRGS): Uma mulher branca de 67 anos veio à Emergência do HCPA no dia 24/02/2002 com queixa de dor nas costas contínua, com início há aproximadamente 18 h, acompanhada de febre, calafrios e tosse com expectoração esbranquiçada. Relatava ter tido febre e ser portadora de hipertensão arterial sistêmica (HAS), sem tratamento, e uso de fumo. O exame físico mostrou estado geral regular, sensório deprimido, TA= 130/80 mmHg, temperatura axilar= 36,2 o C e saturação de 02 = 95%, em ar ambiente. A ausculta pulmonar mostrou murmúrio vesicular uniformemente diminuído, roncos difusos e estertores crepitantes na base direita. A punhopercussão lombar foi dolorosa à direita. Os exames laboratoriais estão descritos nas tabelas 1, 2 e 3
The Kinetic Sunyaev-Zel'dovich Effect from Reionization
During the epoch of reionization, local variations in the ionized fraction
(patchiness) imprint arcminute-scale temperature anisotropies in the CMB
through the kinetic Sunyaev-Zel'dovich (kSZ) effect. We employ an improved
version of an analytic model of reionization devised in Furlanetto et al.(2004)
to calculate the kSZ anisotropy from patchy reionization. This model uses
extended Press-Schechter theory to determine the distribution and evolution of
HII bubbles and produces qualitatively similar reionization histories to those
seen in recent numerical simulations. We find that the angular power spectrum
of the kSZ anisotropies depends strongly on the size distribution of the HII
bubbles and on the duration of reionization. In addition, we show that upcoming
measurements of the kSZ effect should be able to distinguish between several
popular reionization scenarios. In particular, the amplitude of the patchy
power spectrum for reionization scenarios in which the IGM is significantly
ionized by Population III stars (or by mini-quasars/decaying particles) can be
larger (or smaller) by over a factor of 3 than the amplitude in more
traditional reionization histories (with temperature anisotropies that range
between 0.5 and 3 micro-Kelvin at l = 5000). We highlight the differences in
the kSZ signal between many possible reionization morphologies and discuss the
constraints that future observations of the kSZ will place on this epoch.Comment: 14 pages, 10 figures. Accepted for publication in Ap
Cosmic 21-cm Fluctuations as a Probe of Fundamental Physics
Fluctuations in high-redshift cosmic 21-cm radiation provide a new window for
observing unconventional effects of high-energy physics in the primordial
spectrum of density perturbations. In scenarios for which the initial state
prior to inflation is modified at short distances, or for which deviations from
scale invariance arise during the course of inflation, the cosmic 21-cm power
spectrum can in principle provide more precise measurements of exotic effects
on fundamentally different scales than corresponding observations of cosmic
microwave background anisotropies.Comment: 8 pages, 2 figure
Cosmic histories of star formation and reionization: An analysis with a power-law approximation
With a simple power-law approximation of high-redshift () star
formation history, i.e., , we
investigate the reionization of intergalactic medium (IGM) and the consequent
Thomson scattering optical depth for cosmic microwave background (CMB) photons.
A constraint on the evolution index is derived from the CMB optical
depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP)
experiment, which reads ,
where the free parameter is the number of the escaped
ionizing ultraviolet photons per baryon. Moreover, the redshift for full
reionization, , can also be expressed as a function of as well as
. By further taking into account the implication of the
Gunn-Peterson trough observations to quasars for the full reionization
redshift, i.e., , we obtain
and .
For a typical number of of ionizing photons released per baryon of
normal stars, the fraction of these photons escaping from the stars, , can be constrained to within the range of .Comment: 10 pages, 4 figures, accepted for publication in JCA
Metal Enrichment in the Reionization Epoch
The presence of elements heavier than helium ("metals") is of fundamental
importance for a large number of astrophysical processes occurring in planet,
star and galaxy formation; it also affects cosmic structure formation and
evolution in several ways. Even a small amount of heavy elements can
dramatically alter the chemistry of the gas, opening the path to complex
molecules. Metals might enhance the ability of the gas to radiate away its
thermal energy, thus favoring the formation of gravitationally bound objects;
they can also condensate in a solid phase (dust grains), partly or totally
blocking radiation from luminous sources. Finally, they represent useful
tracers of energy deposition by stars and probe the physical properties of the
environment by absorption or emission lines. Last, but certainly not least,
life -- as we know it on Earth -- is tightly related to the presence of at
least some of the heavy elements. In this pedagogical review I will concentrate
on the connection between early metal enrichment and cosmic reionization. As we
will see these two processes are intimately connected and their joint study
might turn out to be fundamental in understanding the overall evolution of the
Universe during the first billion years after the Big Bang, an epoch
corresponding to redshifts z>6.Comment: Book chapter in Understanding the Epoch of Cosmic Reionization:
Challenges and Progress, Springer International Publishing, Ed. Andrei
Mesinger, ISBN 978-3-319-21956-1. arXiv admin note: text overlap with
arXiv:astro-ph/0007248 by other author
Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array
We apply two methods to estimate the 21~cm bispectrum from data taken within
the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA).
Using data acquired with the Phase II compact array allows a direct bispectrum
estimate to be undertaken on the multiple redundantly-spaced triangles of
antenna tiles, as well as an estimate based on data gridded to the -plane.
The direct and gridded bispectrum estimators are applied to 21 hours of
high-band (167--197~MHz; =6.2--7.5) data from the 2016 and 2017 observing
seasons. Analytic predictions for the bispectrum bias and variance for point
source foregrounds are derived. We compare the output of these approaches, the
foreground contribution to the signal, and future prospects for measuring the
bispectra with redundant and non-redundant arrays. We find that some triangle
configurations yield bispectrum estimates that are consistent with the expected
noise level after 10 hours, while equilateral configurations are strongly
foreground-dominated. Careful choice of triangle configurations may be made to
reduce foreground bias that hinders power spectrum estimators, and the 21~cm
bispectrum may be accessible in less time than the 21~cm power spectrum for
some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS
The EoR Sensitivity of the Murchison Widefield Array
Using the final 128 antenna locations of the Murchison Widefield Array (MWA),
we calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum
of red- shifted 21 cm emission for a fiducial model and provide the tools to
calculate the sensitivity for any model. Our calculation takes into account
synthesis rotation, chro- matic and asymmetrical baseline effects, and excludes
modes that will be contaminated by foreground subtraction. For the fiducial
model, the MWA will be capable of a 14{\sigma} detection of the EoR signal with
one full season of observation on two fields (900 and 700 hours).Comment: 5 pages, 4 figures, 1 table, Accepted for publication in MNRAS
Letters. Supplementary material will be available in the published version,
or by contacting the author
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