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Epoch of reionization
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MIT's Jacqueline Hewitt and HERA team given $6M boost to detect cosmic dawn

This week, the Hydrogen Epoch of Reionization Array (HERA) telescope project team was awarded a grant from the Gordon and Betty Moore Foundation to MIT to expand the HERA telescope in South Africa to begin looking for the effects of light from the first generation of stars that formed in the universe.
HERA, an international project led by researchers at the University of California at Berkeley, with initial funding from the National Science Foundation (NSF), is looking for signals from the "epoch of reionization" (EoR) when 90 percent of the hydrogen atoms created in the early universe were destroyed by the first luminous stars and black holes.

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RE: The Reionisation epoch
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Title: A new parametrisation of the reionisation history
Author: Marian Douspis, Nabila Aghanim, Stéphane Ili, Mathieu Langer

Motivated by the current constraints on the epoch of reionisation from recent cosmic microwave background observations, ionising background measurements of star-forming galaxies, and low redshifts line-of-sight probes, we propose a new data-motivated parameterisation of the history of the average ionisation fraction. This parameterisation describes a flexible redshift-asymmetric reionisation process in two regimes that is capable of fitting all the current constraints.

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Ghostly galaxies burned off mysterious cosmic fog

Ghostly galaxies in the distant universe are almost certainly the culprits behind a mysterious change in intergalactic gas that allows us to see across the cosmos. Although these galaxies are too faint to be spotted by current telescopes, future instruments could soon reveal their presence.
About 300,000 years after the big bang, the hydrogen that filled the universe cooled and became neutral and opaque, plunging everything into the so-called cosmic dark ages. Any visible wavelengths from early stars were quickly absorbed by the gas, which formed a cosmic fog that persisted for almost a billion years.

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Title: Exploring the Cosmic Reionisation Epoch in Frequency Space: An Improved Approach to Remove the Foreground in 21 cm Tomography
Authors: Jingying Wang, Haiguang Xu, Tao An, Junhua Gu, Xueying Guo, Weitian Li, Yu Wang, Chengze Liu, Olivier Martineau-Huynh, Xiang-Ping Wu

Aiming to correctly restore the redshifted 21 cm signals emitted by the neutral hydrogen during the cosmic reionisation processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space to investigate whether they works satisfactorily with complex foreground, by quantitatively evaluate the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterise both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias b and average ionisation fraction x_e of the reionisation processes, at z=8 and the noise level of 60 mK we find that, although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of Mpc-scale components of the 21 cm signals (75% for \gtrsim 6h^{-1} Mpc scales and 34% for \gtrsim 1h^{-1} Mpc scales) is lost because it tends to be mis-identified as part of the foreground when single-narrow-segment separation approach is applied. The best restoration of the 21 cm signals and the tightest determination of b and x_e can be obtained with the three-narrow-segment fitting technique as proposed in this paper. Similar results can be obtained at other redshifts.

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Title: Kickstarting Reionisation with the First Black Holes: the effects of second-order perturbation theory in pre-reionisation volumes
Authors: Kelly Holley-Bockelmann, John H. Wise, Manodeep Sinha

We explore structure formation in the dark ages (z ~ 30-6) using two well-known methods for initialising cosmological N-body simulations. Overall, both the Zel'dovich approximation (ZA) and second order Lagrangian perturbation theory (LPT) are known to produce accurate present-day dark matter halo mass functions. However, since the LPT method drives more rapid evolution of dense regions, it increases the occurrence of rare massive objects -- an effect that is most pronounced at high redshift. We find that LPT produces more halos that could harbour Population III stars and their black hole remnants, and they produce them earlier. Although the differences between the LPT and ZA mass functions are nearly erased by z=6, this small boost to the number and mass of black holes more than doubles the Reionised volume of the early Universe. We discuss the implications for reionisation and massive black hole growth.

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Title: Detecting the Rise and Fall of the First Stars by Their Impact on Cosmic Reionisation
Authors: Kyungjin Ahn, Ilian T. Iliev, Paul R. Shapiro, Garrelt Mellema, Jun Koda, Yi Mao

The intergalactic medium was reionised before redshift z~6, most likely by starlight which escaped from early galaxies. The very first stars formed when hydrogen molecules (H2) cooled gas inside the smallest galaxies, minihalos of mass between 10^5 and 10^8 solar masses. Although the very first stars began forming inside these minihalos before redshift z~40, their contribution has, to date, been ignored in large-scale simulations of this cosmic reionisation. Here we report results from the first reionisation simulations to include these first stars and the radiative feedback that limited their formation, in a volume large enough to follow the crucial spatial variations that influenced the process and its observability. We show that reionisation began much earlier with minihalo sources than without, and was greatly extended, which boosts the intergalactic electron-scattering optical depth and the large-angle polarization fluctuations of the cosmic microwave background significantly. Although within current WMAP uncertainties, this boost should be readily detectable by Planck. If reionisation ended as late as z_ov<~7, as suggested by other observations, Planck will thereby see the signature of the first stars at high redshift, currently undetectable by any other probe.

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Very Large Telescope details cosmic timeline

Astronomers have used the Very Large Telescope (VLT) in Chile to study a fundamental change in the cosmos more than 13 billion years ago.
The scientists studied a series of galaxies through time to determine the pace at which the neutral hydrogen that pervaded the Universe back then was turned into a diffuse gas of highly charged particles.

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Distant Galaxies Reveal The Clearing of the Cosmic Fog

Scientists have used ESO's Very Large Telescope to probe the early Universe at several different times as it was becoming transparent to ultraviolet light. This brief but dramatic phase in cosmic history - known as reionisation - occurred around 13 billion years ago. By carefully studying some of the most distant galaxies ever detected, the team has been able to establish a timeline for reionisation for the first time. They have also demonstrated that this phase must have happened quicker than astronomers previously thought.
An international team of astronomers used the VLT as a time machine, to look back into the early Universe and observe several of the most distant galaxies ever detected. They have been able to measure their distances accurately and find that we are seeing them as they were between 780 million and a billion years after the Big Bang.

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Epoch of Reionisation
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Astronomer opens new window into early universe

Thirteen billion years ago our universe was dark. There were neither stars nor galaxies; there was only hydrogen gas left over after the Big Bang. Eventually that mysterious time came to an end as the first stars ignited and their radiation transformed the nearby gas atoms into ions. This phase of the universe's history is called the Epoch of Reionisation (EoR ), and it is intimately linked to many fundamental questions in cosmology.
But looking back so far in time presents numerous observational challenges. ASU's Judd Bowman and Alan Rogers of Massachusetts Institute of Technology have developed a small-scale radio astronomy experiment designed to detect a never-before-seen signal from the early universe during this period of time, a development that has the potential to revolutionize the understanding of how the first galaxies formed and evolved.

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Reionisation of the universe
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Title: How Dark Matter Reionised The Universe
Authors: Alexander V. Belikov, Dan Hooper

Although empirical evidence indicates that that the universe's gas had become ionised by redshift z ~ 6, the mechanism by which this transition occurred remains unclear. In this article, we explore the possibility that dark matter annihilations may have played the dominant role in this process. Energetic electrons produced in these annihilations can scatter with the cosmic microwave background to generate relatively low energy gamma rays, which ionise and heat gas far more efficiently than higher energy prompt photons. In contrast to previous studies, we find that viable dark matter candidates with electroweak scale masses can naturally provide the dominant contribution to the reionisation of the universe. Intriguingly, we find that dark matter candidates capable of producing the recent cosmic ray excesses observed by PAMELA and/or ATIC are also predicted to lead to the full reionisation of the universe by z ~ 6.

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