707 research outputs found
Source Mergers and Bubble Growth During Reionization
The recently introduced models of reionization bubbles based on extended
Press-Schechter theory (Furlanetto, Zaldarriaga & Hernquist 2004) are
generalized to include mergers of ionization sources. Sources with a recent
major merger are taken to have enhanced photon production due to star
formation, and accretion onto a central black hole if a black hole is present.
This produces a scatter in the number of ionized photons corresponding to a
halo of a given mass and a change in photon production over time for any given
halo mass. Photon production histories, bubble distributions, and ionization
histories are computed for several different parameter and recombination
assumptions; the resulting distributions interpolate between previously
calculated limiting cases.Comment: 44 pages, 11 figures, version to appear in MNRAS. Some discussion of
case with WMAP parameters and expanded explanation
A practical theorem on using interferometry to measure the global 21-cm signal
The sky-averaged, or global, background of redshifted cm radiation is
expected to be a rich source of information on cosmological reheating and
reionizaton. However, measuring the signal is technically challenging: one must
extract a small, frequency-dependent signal from under much brighter spectrally
smooth foregrounds. Traditional approaches to study the global signal have used
single antennas, which require one to calibrate out the frequency-dependent
structure in the overall system gain (due to internal reflections, for example)
as well as remove the noise bias from auto-correlating a single amplifier
output. This has motivated proposals to measure the signal using
cross-correlations in interferometric setups, where additional calibration
techniques are available. In this paper we focus on the general principles
driving the sensitivity of the interferometric setups to the global signal. We
prove that this sensitivity is directly related to two characteristics of the
setup: the cross-talk between readout channels (i.e. the signal picked up at
one antenna when the other one is driven) and the correlated noise due to
thermal fluctuations of lossy elements (e.g. absorbers or the ground) radiating
into both channels. Thus in an interferometric setup, one cannot suppress
cross-talk and correlated thermal noise without reducing sensitivity to the
global signal by the same factor -- instead, the challenge is to characterize
these effects and their frequency dependence. We illustrate our general theorem
by explicit calculations within toy setups consisting of two short dipole
antennas in free space and above a perfectly reflecting ground surface, as well
as two well-separated identical lossless antennas arranged to achieve zero
cross-talk.Comment: 17 pages, 6 figures, published in Ap
Lyman-α polarization intensity mapping
We present a formalism that incorporates hydrogen Lyman-alpha (Lyα) polarization arising from the scattering of radiation in galaxy halos into the intensity mapping approach. Using the halo model, and Lyα emission profiles based on simulations and observations, we calculate auto and cross power spectra at redshifts 3 ≤ z ≤ 13 for the Lyα total intensity, I, polarized intensity, P, degree of polarization, Π=P/I, and two new quantities, the astrophysical E and B modes of Lyα polarization. The one-halo terms of the Πpower spectra show a turnover that signals the average extent of the polarization signal, and thus the extent of the scattering medium. The position of this feature depends on redshift, as well as on the specific emission profile shape and extent, in our formalism. Therefore, the comparison of various Lyα polarization quantities and redshifts can break degeneracies between competing effects, and it can reveal the true shape of the emission profiles, which, in turn, are associated to the physical properties of the cool gas in galaxy halos. Furthermore, measurements of Lyα E and B modes may be used as probes of galaxy evolution, because they are related to the average degree of anisotropy in the emission and in the halo gas distribution across redshifts. The detection of the polarization signal at z∼3–5 requires improvements in the sensitivity of current ground-based experiments by a factor of ∼10, and of ∼100 for space-based instruments targeting the redshifts z∼9–10, the exact values depending on the specific redshift and experiment. Interloper contamination in polarization is expected to be small, because the interlopers need to also be polarized. Overall, Lyα polarization boosts the amount of physical information retrievable on galaxies and their surroundings, most of it not achievable with total emission alone
Combining galaxy and 21cm surveys
Acoustic waves traveling through the early Universe imprint a characteristic
scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale
can be used as a standard ruler to map the expansion history of the Universe, a
technique known as Baryon Acoustic Oscillations (BAO). BAO offer a
high-precision, low-systematics means of constraining our cosmological model.
The statistical power of BAO measurements can be improved if the `smearing' of
the acoustic feature by non-linear structure formation is undone in a process
known as reconstruction. In this paper we use low-order Lagrangian perturbation
theory to study the ability of cm experiments to perform reconstruction
and how augmenting these surveys with galaxy redshift surveys at relatively low
number densities can improve performance. We find that the critical number
density which must be achieved in order to benefit cm surveys is set by
the linear theory power spectrum near its peak, and corresponds to densities
achievable by upcoming surveys of emission line galaxies such as eBOSS and
DESI. As part of this work we analyze reconstruction within the framework of
Lagrangian perturbation theory with local Lagrangian bias, redshift-space
distortions, -dependent noise and anisotropic filtering schemes.Comment: 10 pages, final version to appear in MNRAS, helpful suggestions from
referee and others include
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