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Topic: Reionization

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	Reionization - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-10-08)
		Reionization is a process that occurs after the epoch of galaxies and is the second of the two major phase changes in the universe.
		However, it is known from the lack of absorption lines out to quasars of redshift z=4 that most of the current intergalactic medium consists not of neutral atoms (which would form absorption lines) but rather of ionized plasma with only small pockets of neutral atoms forming the Lyman-alpha forest.
		The standard explanation for reionization is that star light from hot blue population III stars ionizes the intergalactic medium.
	www.encyclopedia-online.info /Reionization (228 words)

	Reionization (Site not responding. Last check: 2007-10-08)
		Reionization is a process that occurs after the epoch of galaxies and is the second of the two major phasechanges in the universe.
		However, it is known from the lack of absorption lines out to quasars of redshift z=4that most of the current intergalactic medium consists notof neutral atoms (which would form absorption lines) but rather of ionized plasma withonly small pockets of neutral atoms forming the Lyman-alphaforest.
		It is believed that reionization has been completed by z=4 because more distantquasars have absorption lines corresponding to neutral hydrogen between us and the quasar while closer quasars do not.
	www.therfcc.org /reionization-145349.html (209 words)

	Reionization - Wikipedia, the free encyclopedia
		In Big Bang cosmology, Reionization is the process that reionized the matter in the universe after the epoch of galaxy formation.
		It is the second of two major phase changes of hydrogen gas in the universe.
		The presence of a Gunn-Peterson trough in the spectra of quasars at z = 6, implying the universe was already a few percent neutral, indicated that perhaps reionization began not much earlier, and that the universe was mostly neutral at redshifts z > 10.
	en.wikipedia.org /wiki/Reionization (535 words)

	Neutralization/chemical reionization tandem mass spectrometry method and apparatus therefor - Patent 5101105
		This method may be termed neutralization/chemical reionization and is implemented by a combination of deceleration and focusing lenses, a combination collision chamber and chemical ionization source, and a suitable set of extraction and focusing lenses.
		During the reionization stage, the protonated reagent gas produced by the electron beam will transfer a proton to the neutralized primary molecules M and to the neutral fragments (formed in the initial high energy collisions) such that all species are reionized.
		The reionization process causes the neutralized molecule, the fragments produced during reionization, as well as the fragments produced during the initial high energy collisions of the primary ion molecules MH+ all to be ionized, and these ionized molecules and fragments exit chamber 40 via slit 44.
	www.freepatentsonline.com /5101105.html (3820 words)

	Galaxy Formation Research Home Page (Site not responding. Last check: 2007-10-08)
		The importance of this process as a sink of ionizing photons during reionization and its implications for the number of ionizing photons required per baryon to ionize the universe were discussed by Shapiro (2001).
		Energy released by a small fraction of the baryons in the universe, which condensed out while the IGM was cold, dark, and neutral, reheated and reionized it by redshift 6, exposing other baryons already condensed into dwarf-galaxy minihaloes to the glare of ionizing radiation.
		Regardless of their effect on the progress of reionization, however, the minihaloes were so abundant that random lines of sight thru the high-z universe should encounter many of them, which suggests that it may be possible to observe the processes described here in the absorption spectra of distant sources.
	galileo.as.utexas.edu /research_reionization.html (491 words)

	Giant Gas Cloud Made of Atoms From First Stars
		This period is known as the Reionization Era of the Universe.
		In addition, Walter also looks forward to studying other objects deeper into the era of reionization, both with the expanded VLA (EVLA) and with the Atacama Large Millimeter Array (ALMA), a joint North America-Europe project to be built in Chile.
		Followup observations at the W.M. Keck Observatory in Hawaii showed a clear signature of light absorption indicating that the object is seen at the end of the reionization era.
	www.nrao.edu /pr/2003/j1148 (1331 words)

	Galaxy Formation and Cosmology
		Based on a recently proposed scenario on the early formation of massive fl holes, the possibility that the universe is reionized due to the UV radiation from the fl holes is investigated.
		The reionization epoch depends upon the power-law index of the density fluctuations at the recombination epoch.
		The reionization history in a clumpy universe is pursued by solving 3D radiative transfer equation for the permeation of diffuse UV photons.
	www.rccp.tsukuba.ac.jp /Astro/galform-e.html (923 words)

	Rennan Barkana: Reionization
		This process is called reionization, where the "re" comes from this entire story: First of all the gas was hot and ionized, then it became cool and neutral, and finally it again became heated and ionized, this time by radiation from stars and quasars.
		This process was gradual, as more and more galaxies formed, and "complete reionization" refers to the time when all the low-density gas in the universe had been ionized, and only a small fraction of the gas which was in and near galaxies, and very dense, still remained neutral.
		For some time, we have known that reionization did actually happen; Observations of the cosmic microwave background, in combination with observations of sources of light in the post-reionization universe, together imply directly that reionization must have happened sometime between 100 and 900 million years after the Big Bang.
	wise-obs.tau.ac.il /~barkana/reion.html (1874 words)

	Professor Piero Madau (Site not responding. Last check: 2007-10-08)
		Piero Madau's research interests in the last few years have focused on theoretical cosmology and the high-redshift universe, especially on the physics of the intergalactic medium and the history of star formation in galaxies.
		Currently, Madau is engaged in determining the impact of reionization on several key cosmological issues, from the role reionization plays in allowing collapsed objects to cool and make stars, to determining the small-scale structure in the temperature fluctuations of the cosmic background radiation.
		Probing the epoch of reionization may provide a means of detecting the onset of the first generation of stars and fl holes in the universe.
	www.ucolick.org /%7Eboard/faculty/madau.html (222 words)

	Reionization (Site not responding. Last check: 2007-10-08)
		The light from the stars in this galaxy could have stripped electrons from the surrounding primordial gas, starting a process called reionization that makes...
		{2} Probe the reionization epoch by robustly determining the...
		If reionization is a process extending over a large redshift interval and the luminosity function doesn't evolve strongly beyond z=6, these data will allow us...
	www.wikiverse.org /reionization (290 words)

	4.1 Microwave Background
		In models where the IGM does not reionize, the probability of scattering after the photon-matter decoupling epoch is low, and the Sachs-Wolfe effect dominates the anisotropies at angular scales larger than a few degrees.
		However if reionization occurs, the scattering probability increases substantially and the matter structures, which develop large bulk motions relative to the comoving background, induce Doppler shifts on the scattered CMBR photons and leave an imprint of the surface of last scattering.
		They considered two possible scenarios of reionization: A model that suffers early and gradual (EG) reionization of the IGM as caused by the photoionizing UV radiation emitted by decaying neutrinos, and the late and sudden (LS) scenario as might be applicable to the case of an early generation of star formation activity at high redshifts.
	relativity.livingreviews.org /Articles/lrr-1998-9/node13.html (971 words)

	CITA Research 2001: Cosmology and CMB (Site not responding. Last check: 2007-10-08)
		The observed reionization of the universe, and the presence of massive high-redshift quasars, both place strong constraints on WDM models.
		The central stage of reionization is the overlap stage, during which the ionized-hydrogen bubbles produced by individual sources overlap each other and reionize the low-density gas which takes up most of the volume of the universe.
		He is exploring a number of scenarios for reionization, depending on various possible ionizing source populations.
	www.cita.utoronto.ca /~fiege/AnnRep/ResearchPages/cosmo.html (3099 words)

	E-Cass:2000-JS - Razoumov's Plaskett Lecture
		Coincidentally, this is the epoch very poorly understood at the moment, because at this stage the density inhomogeneities enter a very non-linear regime to form the first gravitationally bound objects, whose internal evolution gave rise to stars and, perhaps, more massive luminous objects which ionized the medium.
		Understanding details of reionization would help us to study the role of feedback mechanisms on subsequent structure formation, as well as learn something about the first generation of objects by studying their imprint on the IGM.
		Assuming that most ionizing photons are not very energetic, that is reionization is not caused by soft X-rays from quasars or star forming regions, reionization is bound to demonstrate a very patchy character.
	www.astro.ubc.ca /E-Cass/2000-JS/razoumov.html (1861 words)

	M. G. Santos Research (Site not responding. Last check: 2007-10-08)
		The free electrons in the reionized (or reionizing) intergalactic medium with peculiar velocities lead to new anisotropies as the CMB photons scatter off of them.
		We have studied the contributions from inhomogeneous reionization to arcminute scale CMB anisotropies and shown that inhomogeneities in the ionization fraction, rather than in the mean density, dominate both the temperature and the polarization power spectra.
		Reionization can significantly bias cosmological parameter estimates and degrade gravitational lensing potential reconstruction from temperature maps but not from polarization maps.
	bubba.ucdavis.edu /~santos/reion.html (213 words)

	Reionization Review (Barkana & Loeb) (Site not responding. Last check: 2007-10-08)
		The formation of the first stars and quasars marks the transformation of the universe from its smooth initial state to its clumpy current state.
		In popular cosmological models, the first sources of light began to form at a redshift z=30 and reionized most of the hydrogen in the universe by z=7.
		Current observations are at the threshold of probing the hydrogen reionization epoch.
	wise-obs.tau.ac.il /%7Ebarkana/review.html (186 words)

	MPA :: Current Research Highlight :: December 2004
		Field 1959) that neutral hydrogen in the IGM may be directly detectable at frequencies that fall in the radio band (in the range 70-170 MHz) and measurements at different frequencies should allow us to probe accurately the structure and the evolution of the reionizing gas.
		The next generation of low-frequency radio telescopes should be sensitive enough to measure such fluctuations and to probe the structure of the reionization process directly.
		In conclusion, the next generation of low-frequency radio telescopes will be able to map, for the first time, the temporal evolution of the reionization process and to shed light on the nature of the sources that caused it.
	www.mpa-garching.mpg.de /mpa/research/current_research/hl2004-12/hl2004-12-en.html (589 words)

	Reionization (Site not responding. Last check: 2007-10-08)
		scale invariant adiabatic ones, degree scale anisotropy detections are already severely constraining the amount of reionization allowable.
		Still, it is useful to recall the basic physical effects associated with reionization.
		Figure: Reionization Effects from Hu and White (1995)
	background.uchicago.edu /~whu/physics/aux/secondary.html (374 words)

	The First Stars and Evolution of the Early Universe (06-2a) (Site not responding. Last check: 2007-10-08)
		Prior to the formation of these stars, the universe mostly consists of neutral H and He atoms and it remains dark due to absorption of light by these atoms.
		The ultraviolet photons from the first stars contribute to the reionization of the early universe which marks the end of the "cosmic dark age." These stars also provide the first significant amounts of heavy elements in the universe.
		Reionization and metal enrichment of the universe have been investigated by a number of groups.
	int.phys.washington.edu /PROGRAMS/06-2a.html (477 words)

	CosmoCoffee :: View topic - [astro-ph/0503166] The influence of non-uniform reionization on the CMB
		We investigate the impact of spatial variations in the ionized fraction during reionization on temperature anisotropies in the CMB.
		The effect of patchy reionization is largest on scales where the primordial CMB anisotropies dominate.
		Improvements in the theoretical modeling of the reionization epoch will become increasingly important to interpret the results of upcoming experiments.
	www.cosmocoffee.info /viewtopic.php?p=510 (852 words)

	[No title]
		N Gnedin was one of the first to attempt to simulate the full problem of computing how ionizing photons emanate from star-forming galaxies, and ionize their surroundings.
		The evolution of the hydrogen optical depth suggests that HeII reionization took place between redshifts 3.1 and 3.4.
		The evolution of the temperature before that suggests HI reionization took place after redshift 9.
	www.ast.cam.ac.uk /~rtnigm/reion/RTNreionization.html (616 words)

	Reionizing the Universe
		However, in the last few years several observations have focused the attention of the cosmological community on one of the least understood processes in the Universe's evolution; the epoch of reionization of the IGM.
		As a result, a large amount of effort is currently dedicated to understanding the physical processes that trigger and govern the evolution of this epoch and their ramifications on subsequent structure formation.
		Our hope is to focus the attention of both communities on the observational properties of the expected measurements and the various physical processes that might produce them, within the larger context of current cosmological models and the physics of the IGM.
	www.astro.rug.nl /~cosmo05 (767 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		LOFAR: Mapping the neutral hydrogen distribution of the Universe during reionization and the Dark Ages.
		This provides a tremendous amount of information on the precursors of stars, galaxies and quasars that we see around us today and about the evolution of the baryonic and dark-matter distributions in the infant universe.
		To map the neutral hydrogen during reionization and the Dark Ages - where still little to nothing is known - the Kapteyn Institute/RUG is involved in the Low Frequency Array (LOFAR; http://www.lofar.org/), a telescope build some 50 km south of Groningen and funded by the Dutch government.
	www.astro.rug.nl /~koopmans/LOFAR_project.txt (417 words)

	Cosmological Reionization and the End of the Dark Ages / Events & Calendar / CITA
		The universe was reionized by redshift z ~ 6 by a small fraction of the baryons in the universe, which released energy following their condensation out of a cold, dark, and neutral IGM into the earliest galaxies.
		The theory of this reionization is a critical missing link in the theory of galaxy formation.
		Its numerous observable consequences include effects on the spectrum, anisotropy and polarization of the cosmic microwave background and signatures of high-redshift star and quasar formation.
	www.cita.utoronto.ca /index.php/events_calendar/cosmological_reionization_and_the_end_of_the_dark_ages (206 words)

	Cosmology Group: CMB (Site not responding. Last check: 2007-10-08)
		Typically reionization studies assume a sudden phase transition, with the intergalactic gas moving from a fully neutral to a fully ionized state at a fixed redshift.
		We find, however, that prompt reionization models give a reasonable estimate of the epoch at which the mean cosmic ionization fraction was ~50%, and provide a very good measure of the overall Thomson optical depth.
		As in Bruscoli {\it et al.} (2000), we consider a set of reionization simulations studied in Ciardi {\it et al.} (2000) (CFGJ), which model reionization from stellar sources, including Population III objects.
	www.arcetri.astro.it /science/cosmology/CMB/cmb_fast.html (933 words)

	HubbleSite - Release Text about "Hubble Approaches the Final Frontier: The Dawn of Galaxies"
		In the past couple decades astronomers have amassed evidence that we live in a reionized or "refried universe." This so-called reionization epoch was a critical watershed for the evolving universe.
		The epoch of reionization is thought to have ended 0.5 to one billion years after the big bang.
		The amount of reionizing light at redshifts 7-8 appears to be lower than what is seen only 200 million years later at redshift 6.
	www.hubblesite.org /newscenter/newsdesk/archive/releases/2004/28/text (1369 words)

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