1,178 research outputs found
The 21-cm Background from the Cosmic Dark Ages: Minihalos and the Intergalactic Medium before Reionization
The H atoms inside minihalos (i.e. halos with virial temperatures T_vir <
10^4 K, in the mass range roughly from 10^4 M_sun to 10^8 M_sun) during the
cosmic dark ages in a LCDM universe produce a redshifted background of
collisionally-pumped 21-cm line radiation which can be seen in emission
relative to the cosmic microwave background (CMB). Previously, we used
semi-analytical calculations of the 21-cm signal from individual halos of
different mass and redshift and the evolving mass function of minihalos to
predict the mean brightness temperature of this 21-cm background and its
angular fluctuations. Here we use high-resolution cosmological N-body and
hydrodynamic simulations of structure formation at high redshift (z > 8) to
compute the mean brightness temperature of this background from both minihalos
and the intergalactic medium (IGM) prior to the onset of Ly-alpha radiative
pumping. We find that the 21-cm signal from gas in collapsed, virialized
minihalos dominates over that from the diffuse shocked gas in the IGM.Comment: 8 pages, 5 figures. To appear in proceedings of UC Irvine May 2005
workshop on "First Light & Reionization", eds. E. Barton & A. Cooray, New
Astronomy Reviews, in pres
Measuring the History of Cosmic Reionization using the 21-cm PDF from Simulations
The 21-cm PDF (i.e., distribution of pixel brightness temperatures) is
expected to be highly non-Gaussian during reionization and to provide important
information on the distribution of density and ionization. We measure the 21-cm
PDF as a function of redshift in a large simulation of cosmic reionization and
propose a simple empirical fit. Guided by the simulated PDF, we then carry out
a maximum likelihood analysis of the ability of upcoming experiments to measure
the shape of the 21-cm PDF and derive from it the cosmic reionization history.
Under the strongest assumptions, we find that upcoming experiments can measure
the reionization history in the mid to late stages of reionization to 1-10%
accuracy. Under a more flexible approach that allows for four free parameters
at each redshift, a similar accuracy requires the lower noise levels of
second-generation 21-cm experiments.Comment: 13 pages, 16 figures, submitted to MNRA
Current models of the observable consequences of cosmic reionization and their detectability
A number of large current experiments aim to detect the signatures of the cosmic reionization at redshifts z > 6. Their success depends crucially on understanding the character of the reionization process and its observable consequences and designing the best strategies to use. We use large-scale simulations of cosmic reionization to evaluate the reionization signatures at redshifted 21-cm and small-scale cosmic microwave background (CMB) anisotropies in the best current model for the background universe, with fundamental cosmological parameters given by Wilkinson Microwave Anisotropy Probe three-year results. We find that the optimal frequency range for observing the `global step of the 21-cm emission is 120150 MHz, while statistical studies should aim at 140160 MHz, observable by GMRT. Some strongly non-Gaussian brightness features should be detectable at frequencies up to ~190 MHz. In terms of sensitivity-signal trade-off relatively low resolutions, corresponding to beams of at least a few arcminutes, are preferable. The CMB anisotropy signal from the kinetic SunyaevZel'dovich effect from reionized patches peaks at tens of K at arcminute scales and has an rms of ~1 K, and should be observable by the Atacama Cosmology Telescope and the South Pole Telescope. We discuss the various observational issues and the uncertainties involved, mostly related to the poorly known reionization parameters and, to a lesser extend, to the uncertainties in the background cosmology
Auto-parallel equation as Euler-Lagrange's equation in spaces with affine connections and metrics
The auto-parallel equation over spaces with affine connections and metrics is
considered as a result of the application of the method of Lagrangians with
covariant derivatives (MLCD) on a given Lagrangian density.Comment: 19 pages, LaTe
Nonlinear Bias of Cosmological Halo Formation in the Early Universe
We present estimates of the nonlinear bias of cosmological halo formation,
spanning a wide range in the halo mass from to , based upon both a suite of high-resolution cosmological
N-body simulations and theoretical predictions. The halo bias is expressed in
terms of the mean bias and stochasticity as a function of local overdensity
(), under different filtering scales, which is realized as the density
of individual cells in uniform grids. The sampled overdensities span a range
wide enough to provide the fully nonlinear bias effect on the formation of
haloes. A strong correlation between and halo population overdensity
is found, along with sizable stochasticity. We find that the
empirical mean halo bias matches, with good accuracy, the prediction by the
peak-background split method based on the excursion set formalism, as long as
the empirical, globally-averaged halo mass function is used. Consequently, this
bias formalism is insensitive to uncertainties caused by varying halo
identification schemes, and can be applied generically. We also find that the
probability distribution function of biased halo numbers has wider distribution
than the pure Poisson shot noise, which is attributed to the sub-cell scale
halo correlation. We explicitly calculate this correlation function and show
that both overdense and underdense regions have positive correlation, leading
to stochasticity larger than the Poisson shot noise in the range of haloes and
halo-collapse epochs we study.Comment: 18 pages, 8 figures, in press for publication in MNRAS; supplementary
material (additional 16 figures) separately supplied (supplement.pdf) as a
part of source file
Self-regulated reionization
Recently, we have presented the first large-scale radiative transfer
simulations of reionization. Here we present new simulations which extend the
source halo mass range downward to 10^8M_solar, to capture the full range of
halo masses thought to be primarily responsible for reionization by their star
formation following atomic hydrogen radiative cooling and gravitational
collapse. Haloes below about 10^9M_solar, however, are subject to Jeans-mass
filtering in the ionized regions, which suppresses their baryonic content and
their ability to release ionizing radiation. By including these smaller-mass
haloes but accounting for their suppression, too, we find that reionization is
``self-regulating,'' as follows. As the mean ionized fraction rises, so does
the fraction of the volume within which suppression occurs. Hence, the degree
of suppression is related to the mean ionized fraction. Since low-mass haloes
with high emissivity achieve a given mean ionized fraction earlier than do
those with low efficiency, Jeans-mass filtering compensates for the difference
in the emissivity of the suppressible haloes in these two cases. As a result,
in the presence of lower-mass source haloes, reionization begins earlier, but
the later stages of reionization and the time of overlap are dictated by the
efficiency of the higher-mass haloes, independent of the efficiency of the
suppressible, lower-mass haloes. Reionization histories consistent with current
observational constraints are shown to be achievable with standard stellar
sources in haloes above 10^8M_solar. Neither minihalos nor exotic sources are
required, and the phenomenon of ``double reionization'' previously suggested
does not occur. (abridged)Comment: 16 pages, 10 figures, most in color. MNRAS, in print. Replaced to
match the accepted version. High-quality images and movies can be found at
http://www.cita.utoronto.ca/~iliev/dokuwiki/doku.php?id=reionization_sim
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