We study the impact of inhomogeneous hydrogen reionization on the thermal evolution of the intergalactic medium (IGM) using hydrodynamic + radiative transfer simulations where reionization is completed either early (z ~ 9) or late (z ~ 6). In general, we find that low-density gas near large-scale overdensities is ionized and heated earlier than gas in the large-scale, underdense voids. Furthermore, at a later time the IGM temperature is inversely related to the reionization redshift because gas that is heated earlier has more time to cool through adiabatic expansion and Compton scattering. Thus, at the end of reionization the median temperature-density relation is an inverted power-law with slope gamma-1 ~ -0.2, in both models. However, at fixed density, there is up to order unity scatter in the temperature due to the distribution of reionization redshifts. Because of the complex equation-of-state, the evolved IGM temperature-density relations for the redshift range 4 < z < 6 can still have significant curvature and scatter. These features must be taken into account when interpreting the Lyman alpha absorption in high redshift quasar spectra.
The temperature of the diffuse, photo-heated intergalactic medium (IGM) depends on its reionization history because the thermal time scales are long. The widths of the hydrogen Lyman-alpha absorption lines seen in the spectra of distant quasars that arise in the IGM can be used to determine its temperature. We use a wavelet analysis of the Lyman-alpha forest region of quasar spectra to demonstrate that there is a relatively sudden increase in the line widths between redshifts z=3.5 and 3.0, which we associate with entropy injection resulting from the reionization of HeII. The subsequent fall-o…
We use numerical hydrodynamical simulations of early structure formation in a LCDM universe to investigate the spin temperature and 21cm brightness of the diffuse intergalactic medium (IGM) prior to the epoch of cosmic reionization, at z<20. In the absence of any radiative heating, collisions between neutral hydrogen atoms can efficiently decouple the spin temperature from the CMB only in dense minihalos and filaments. Shock heated gas shines in emission, surrounded by cooler gas visible in absorption. In the case of a warm, mostly neutral IGM, produced here by X-ray emission from an early min…
The temperature of the intergalactic medium (IGM) is set by the competition between photoheating and adiabatic cooling, which are usually assumed to define a tight equation of state in which the temperature increases monotonically with density. We use a semi-analytic model, accurate at low to moderate IGM densities (<5 times the mean), to show that inhomogeneous reionization can substantially modify these expectations. Because reionization is driven by biased sources, dense pockets of the IGM are likely to be ionized first. As a result, voids initially remain cool while dense regions are heate…
Energy released by a small fraction of the baryons in the universe, which condensed out of while the IGM was cold, dark, and neutral,reheated and reionized it, exposing gas clouds within it to the glare of ionizing radiation. The first gas dynamical simulations of the photoevaporation of an intergalactic cloud by a quasar, including radiative transfer, are presented, along with a few observational diagnostics.
The bulk of the hydrogen in the universe transformed from neutral to ionized somewhere in the redshift interval 5 < z < 40, most likely due to ionizing photons produced by an early generation of stars or mini-quasars. The resulting free electrons, interacting with the CMB photons via Thomson scattering, are a mixed blessing, providing both a probe of the epoch of the first stars and a contaminant to the pristine primary anisotropy. Here we review our current knowledge of reionization with emphasis on inhomogeneities and describe the possible connections to CMB anisotropy.
The temperature of the low-density intergalactic medium is set by the balance between adiabatic cooling resulting from the expansion of the universe, and photo-heating by the UV-background. A sudden injection of entropy from the reionization will increase the temperature of the gas, leading to a broadening of the hydrogen Lyman-alpha absorption lines produced in the IGM, and observed in the spectra of background quasars. We present a method based on wavelets to characterise objectively the line widths of such absorption lines. We use high resolution hydrodynamical simulations to demonstrate th…
The thermal history of the intergalactic medium (IGM) after reionization is to a large extent determined by photoheating. Here we demonstrate that calculations of the photoheating rate which neglect radiative transfer effects substantially underestimate the energy input during and after reionization. The neglect of radiative transfer effects results in temperatures of the IGM which are too low by a factor of two after HeII reionization. We briefly discuss implications for the absorption properties of the IGM and the distribution of baryons in shallow potential wells.
We use hydrodynamic cosmological simulations in a 9.6 Mpc box to explore the evolution of the intergalactic medium (IGM) transmissivity from z=2 through the epoch of reionization. Reionization is achieved through an ultraviolet background (UVB) that includes evolving stellar and QSO source populations. We construct and analyze noiseless synthetic HI Lya absorption spectra along lines of sight through our continuously evolving box and find a smooth evolution of the effective optical depth under a power law up to the epoch of reionization. Crossing into the epoch of reionization, both the mean t…
Following the completion of cosmic reionization, the mean-free-path of ionizing photons was set by a population of Ly-limit absorbers. As the mean-free-path steadily grew, the intensity of the ionizing background also grew, thus lowering the residual neutral fraction of hydrogen in ionization equilibrium throughout the diffuse intergalactic medium (IGM). Ly-alpha photons provide a sensitive probe for tracing the distribution of this residual hydrogen at the end of reionization. Here we calculate the cosmic variance among different lines-of-sight in the distribution of the mean Ly-alpha optical…
Recent years have seen major advances in understanding the state of the intergalactic medium (IGM) at high redshift. Some aspects of this understanding are reviewed here. In particular, we discuss: (1) Different probes of IGM like Gunn-Peterson test, CMBR anisotropies, and neutral hydrogen emission from reionization, and (2) some models of reionization of the universe.
We examine the effect of inhomogeneous reionization on the galaxy power spectrum and the consequences for probing dark energy. To model feedback during reionization, we apply an ansatz setting the galaxy overdensity proportional to the underlying ionization field. Thus, inhomogeneous reionization may leave an imprint in the galaxy power spectrum. We evolve this imprint to low redshift and use the Fisher-matrix formalism to assess the effect on parameter estimation. We show that a combination of low- (z=0.3) and high- (z=3) redshift galaxy surveys can constrain the size of cosmological HII regi…
We develop an efficient method to study the effects of reionization history on the temperature-density relation of the intergalactic medium in the low density limit (overdensity less than 5). It is applied to the study of photo-reionization models in which the amplitude, spectrum and onset epoch of the ionizing flux, as well as the cosmology, are systematically varied. We find that the mean temperature-density relation at z=2-4 is well approximated by a power-law equation of state for uniform reionization models. We derive analytical expressions for its evolution and exhibit its asymptotic beh…
Lyman-alpha absorption is a prominent cosmological tool for probing both galactic halos and the intergalactic medium at high redshift. We consider a variety of sources that can be used as the Lyman-alpha emitters for this purpose. Among these sources, we argue that quasars are the best probes of the evolution of massive halos, while gamma-ray bursts represent the cleanest sources for studying the reionization of the intergalactic medium.
We show that the gaseous halos of collapsed objects introduce a substantial cumulative opacity to ionizing radiation, even after the smoothly distributed hydrogen in the intergalactic medium has been fully reionized. This opacity causes a delay of around unity in redshift between the time of the overlap of ionized bubbles in the intergalactic medium and the lifting of complete Gunn-Peterson Lyman alpha absorption. The minihalos responsible for this screening effect are not resolved by existing numerical simulations of reionization.
The Doppler parameter distribution of Lyman-alpha absorption is calculated for a set of different reionization histories. The differences in temperature between different reionization histories are as large as a factor three to four depending on the spectrum of the ionizing sources and the redshift of helium reionization. These temperature differences result in observable differences in the Doppler parameter distribution. Best agreement with the observed Doppler parameter distribution between redshift two and four is found if hydrogen and helium are reionized simultaneously at or before redshi…
We consider the effects of inhomogeneous reionization on the distribution of galaxies at high redshifts. Modulation of the formation process of the ionizing sources by large scale density modes makes reionization inhomogeneous and introduces a spread to the reionization times of different regions with the same size. After sources photo-ionize and heat these regions to a temperature $\ga 10^4$K at different times, their temperatures evolve as the ionized intergalactic medium (IGM) expands. The varying IGM temperature makes the minimum mass of galaxies spatially non-uniform with a fluctuation am…
We consider the effect of reionization on the clustering properties of galaxy samples at intermediate redshifts (z~0.3-5.5). Current models for the reionization of intergalactic hydrogen predict that overdense regions will be reionized early, thus delaying the build up of stellar mass in the progenitors of massive lower-redshift galaxies. As a result, the stellar populations observed in intermediate redshift galaxies are somewhat younger and hence brighter in overdense regions of the Universe. Galaxy surveys would therefore be sensitive to galaxies with a somewhat lower dark matter mass in ove…
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 LambdaCDM 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 f…
During the epoch of reionization a large number of photons were produced with frequencies below the hydrogen Lyman limit. After redshifting into the closest resonance, these photons underwent multiple scatterings with atoms. We examine the effect of these scatterings on the temperature of the neutral intergalactic medium (IGM). Continuum photons, emitted between the Ly_alpha and Ly_gamma frequencies, heat the gas after being redshifted into the H Ly_alpha or D Ly_beta resonance. By contrast, photons emitted between the Ly_gamma and Ly-limit frequencies, produce effective cooling of the gas. Pr…
We show that the cosmic star formation rate per comoving volume should exhibit a distinct drop around the reionization redshift, when the HII regions in the intergalactic medium around individual ionizing sources first overlapped. The drop results from the increase in the temperature of the intergalactic medium as it was photo-ionized, and the consequent suppression of the formation of low-mass galaxies. We show quantitatively that the detection of this drop, which is marked by a corresponding fall in the number counts of faint galaxies, should become feasible over the coming decade with the N…
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 fluctu…
Observations of high-redshift Ly-alpha sources are a major tool for studying the high-redshift Universe. We discuss the effect of the reionizing intergalactic medium on the observability of Ly-alpha sources based on large simulations of early structure formation with radiative transfer. This takes into account self-consistently the reionization history, density, velocity and ionization structures and nonlinear source clustering. We find that all fields are highly anisotropic and as a consequence there are very large variations in opacity among the different lines-of-sight. The velocity effects…
The spectra of the first galaxies and quasars in the Universe should be strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by neutral hydrogen (HI) in the intervening intergalactic medium. However, the Lyman-alpha line photons emitted by these sources are not eliminated but rather scatter until they redshift out of resonance and escape due to the Hubble expansion of the surrounding intergalactic HI. We calculate the resulting brightness distribution and the spectral shape of the diffuse Lyman-alpha line emission around high redshift sources, before the intergalactic medium …
Winds from star-forming galaxies provide the most promising explanation for the enrichment of the intergalactic medium with heavy elements. Theoretical and observational arguments indicate that the pollution may have occurred at z > 6; however, direct observational tests of such a scenario are needed. We model starburst winds in the high-redshift universe and find that the fraction of space filled by enriched material varies strongly with the assumed star formation efficiency f_* and the fraction of supernova energy powering each wind, f_esc. We show that metals carried by these winds can be s…
We examine the constraints on the epoch of reionization (redshift z_r) set by recent WMAP-3 observations of tau_e = 0.09 +/- 0.03, the electron-scattering optical depth of the cosmic microwave background (CMB), combined with models of high-redshift galaxy and black hole formation. Standard interpretation begins with the computed optical depth, tau_e = 0.042 +/- 0.003, for a fully ionized medium out to z_r = 6.1 +/- 0.15, including ionized helium, which recombines at z ~ 3. At z > z_r, one must also consider scattering off electrons produced by from early black holes (X-ray pre-ionization) and …
We study contributions to the cosmic microwave background (CMB) bispectrum from non-Gaussianity induced by secondary anisotropies during reionization. Large-scale structure in the reionized epoch both gravitational lenses CMB photons and produces Doppler shifts in their temperature from scattering off electrons in infall. The resulting correlation is potentially observable through the CMB bispectrum. The second-order Ostriker-Vishniac also couples to a variety of linear secondary effects to produce a bispectrum. For the currently favored flat cosmological model with a low matter content and sm…
We use numerical simulations of hydrogen reionization by stellar sources in the context of LCDM cosmogonies to investigate the 21 (1+z) cm radio signal expected from the diffuse intergalactic medium (IGM) prior to the epoch of reionization breakthrough at redshift z_ion. Two reionization scenarios are analyzed in details: an `early reionization' case with z_ion~13, consistent with the recent discovery by the WMAP satellite of a large optical depth to Thomson scattering, and a `late reionization' case with z_ion~8. It is a generic prediction of these models that the background of Lyalpha photon…
Observational studies indicate that the intergalactic medium (IGM) is highly ionized up to redshifts just over 6. A number of models have been developed to describe the process of reionization and the effects of the ionizing photons from the first luminous objects. In this paper, we study the impact of an X-ray background, such as high-energy photons from early quasars, on the temperature and ionization of the IGM prior to reionization, before the fully ionized bubbles associated with individual sources have overlapped. X-rays, which have large mean free paths relative to EUV photons, and thei…
Observations of high-redshift quasars show that the IGM must have been reionized at some redshift $z>5$. If a source of radiation could be observed at the rest-frame Lya wavelength, at a sufficiently high redshift where some of the IGM in the line-of-sight was not yet reionized, the Gunn-Peterson trough should be present. Longward of the Lya wavelength, a damping wing should be observed caused by the neutral IGM whose absorption profile can be predicted. Measuring the shape of this damping wing would provide irrefutable evidence of the observation of the IGM before reionization, and a determin…
We use a large set of hydrodynamical simulations, combined with measurements of the Lyman alpha opacity of the IGM taken from the literature, to obtain robust estimates for the photoionization rate per hydrogen atom at z=5 and 6. We find the photoionization rate drops by a factor of two and four, respectively, compared to our recent measurements at z = 2 - 4. The number of ionizing photons emitted by known sources at z=5 and 6, based on an extrapolation of source numbers below the detection limit and standard assumptions for the relationship between the ionizing emissivity and observed luminos…
Strong intergalactic shocks are a natural consequence of structure formation in the universe. They are expected to deposit large fractions of their energy in relativistic electrons (xi_e~0.05 according to SNR observations) and magnetic fields (xi_B~0.01 according to cluster halo observations). We calculate the synchrotron emission from such shocks using an analytical model, calibrated with a hydrodynamical LCDM simulation. The resulting signal composes a large fraction of the extragalactic radio background (ERB) below 500 MHz. The associated angular fluctuations dominate the sky for frequencie…
I provide estimates of the ultraviolet and visible light luminosity density at z~6 after accounting for the contribution from faint galaxies below the detection limit of deep Hubble and Spitzer surveys. I find the rest-frame V-band luminosity density is a factor of ~2-3 below the ultraviolet luminosity density at z~6. This implies that the maximal age of the stellar population at z~6, for a Salpeter initial mass function, and a single, passively evolving burst, must be <100 Myr. If the stars in z~6 galaxies are remnants of the star-formation that was responsible for ionizing the intergalactic …
Constraints on the ionization structure of the Intergalactic Medium are derived as directly imposed by observations in conjunction with the results of numerical simulations for structure formation. Under the assumption that the population of sources dominating the UV ionizing background at z<6 is the same population which reionized the IGM, it is shown that consistency with measurements of the mean LyA transmitted flux at high redshifts requires the epoch of hydrogen reionization of the IGM to have occurred at a redshift z < 11, independent of the space density of the sources. The upper limit …
Early photoionization of the intergalactic medium is discussed in a nearly model-independent way, in order to investigate whether early structures corresponding to rare Gaussian peaks in a CDM model can photoionize the intergalactic medium sufficiently early to appreciably smooth out the microwave background fluctuations. We conclude that this is indeed possible for a broad range of CDM normalizations and is almost inevitable for unbiased CDM, provided that the bulk of these early structures are quite small, no more massive than about 10^8 solar masses. Typical parameter values predict that re…
We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to study the properties of the intergalactic medium between redshifts z=2.0-2.9. The high-quality optical spectrum allows us to identify approximately 850 HeII absorption components with column densities between N~5X10^11 and $ 10^18 cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the HeII absorption down to an observed wavelength of 920 A. Approximately 1400 HeII absorption components are identified, including 917 HeII Ly-alpha systems and some of their HeII Ly-beta, Ly-gamma, and Ly-delta count…
Near-infrared observations of Lyman-break galaxies at redshifts z~3 are beginning to provide constraints on ages, star-formation histories, dust content, metallicities, and stellar masses. At present, uncertainties of more than an order of magnitude are typical for many of these parameters. It is nonetheless interesting to ask what the stellar-population models imply for the existence and luminosities of Lyman-break galaxies at higher redshift. To this end we examine the inferred star-formation rates in two well-studied samples of galaxies as a function of redshift out to z = 10 for various be…
The temporal evolution of the ionizing UV background radiation field at high redshift provides a probe of the evolution of the early star formation rate. By comparing the observed levels of absorption in the highest redshift quasar spectra to the predictions of a hydrodynamic simulation, we determine the evolution of the photoionization rate Gamma for neutral hydrogen in the intergalactic medium, over the redshift range 4.9 < z < 6.1. After accounting for sampling variance, we infer a sharp increase in Gamma from z~6.1 to z~5.8, probably implying reionization at this redshift. We find a decrea…
We use numerical simulation of cosmological reionization to calculate the secondary CMB anisotropies in a representative flat low density cosmological model. We show that the kinetic Sunyaev-Zel'dovich effect (scattering off of moving electrons in the ionized intergalactic medium) is dominated by the nonlinear hydrodynamic and gravitational evolution of the density and velocity fields, rather than the detailed distribution of the ionization fraction (``patchy reionization'') on all angular scales. Combining our results with the recent calculation of secondary CMB anisotropies by Springel et al…
We report on observations of redshifted HeII 304 A absorption in the QSO HE 2347-4342 (z=2.885, V=16.1) with the GHRS on board HST (FWHM=0.7 A). At the expected position of HeII 304 A absorption, HE 2347-4342 is the most UV-bright high redshift QSO discovered so far. We show that the HeII opacity as a function of redshift is patchy showing spectral regions with low HeII opacity (voids) and regions with high HeII opacity (troughs) and no detectable flux. Combination with high-resolution optical spectra of the Ly_alpha forest using CASPEC at the ESO 3.6m telescope shows that the voids can be exp…
Wasn't this a fun meeting? Yes, except for the rain. This summary highlights scientific themes of the 13th IAP conference: (1) The History of Baryons; (2) The History of Metals; (3) Reionization of the IGM; (4) The Assembly of Galaxies, plus a "wish list" of future projects for observers and theorists.
We report the discovery of a Lyman-alpha-emitting galaxy at redshift z=6.545 serendipitously identified in the course of spectroscopic follow-up of hard X-ray sources on behalf of the Serendipitous Extragalactic X-Ray Source Identification (SEXSI) survey. The line flux of the galaxy, 2.1e-17 erg/cm2/s, is similar to line fluxes probed by narrow-band imaging surveys; the 5.2 square-arcminutes surveyed implies a surface density of z~6.5 Lyman-alpha emitters somewhat higher than that inferred from narrow-band surveys. This source marks the sixth Lyman-alpha-emitting galaxy identified at z~6.5, a …
We reexamine the impact of dark matter (DM) annihilation on the intergalactic medium, taking into account the clumping of DM particles. We find that energy injection from the annihilation of the thermal relic DM particles may significantly raise the gas temperature at high redshifts and leave a strong imprint on the cosmological 21-cm signal, provided the particle mass is below ~1 TeV. Further, we find that while the energy injection from DM annihilation could not alone complete the reionization of the Universe, it could make a significant contribution to the electron optical depth.
A variety of observations now indicate that intergalactic helium was fully ionized by z~3. The most recent measurements of the high-redshift quasar luminosity function imply that these sources had produced ~2.5 ionizing photons per helium atom by that time, consistent with a picture in which the known quasar population drives HeII reionization. Here we describe the distribution of ionized and neutral helium gas during this era. Because the sources were rare and bright (with the photon budget dominated by quasars with luminosities L>L_\star), random fluctuations in the quasar population determi…
Supernova explosions in the early star forming galaxies will accelerate cosmic rays (CRs). CRs are typically confined in the collapsed objects for a short period before escaping into the intergalactic medium (IGM). Galactic outflows can facilitate this escape by advecting CRs into the IGM. An outflow that results in a termination shock can also generate more CRs. We show that the CR protons from the above processes can significantly affect the thermal history of the IGM. Within plausible range of parameters, cosmic ray heating can compensate for adiabatic cooling and explain the measured IGM t…
The intergalactic medium - the cosmic gas that fills the great spaces between the galaxies - is affected by processes ranging from quantum fluctuations in the very early universe to radiative emission from newly-formed stars. This gives the intergalactic medium a dual role as a powerful probe both of fundamental physics and of astrophysics. The heading of fundamental physics includes conditions in the very early universe and basic cosmological parameters. The astrophysics refers to chapters of the long cosmic history of stars and galaxies that are being revealed through the effects of stellar …
We study the observability of the reionization epoch through the 21 cm hyperfine transition of neutral hydrogen. We use a high-resolution cosmological simulation (including hydrodynamics) together with a fast radiative transfer algorithm to compute the evolution of 21 cm emission from the intergalactic medium (IGM) in several different models of reionization. We show that the mean brightness temperature of the IGM drops from dT_b~25 mK to dT_b~0.01 mK during overlap (over a frequency interval of ~25 MHz), while the root mean square brightness temperature fluctuations on small scales drop abrup…
The propagation of cosmological ionization fronts during the reionization of the universe is strongly influenced by small-scale gas inhomogeneities due to structure formation. These inhomogeneities include both collapsed minihalos, which are generally self-shielding, and lower-density structures, which are not. The minihalos are dense and sufficiently optically-thick to trap intergalactic ionization fronts, blocking their path and robbing them of ionizing photons until the minihalo gas is expelled as an evaporative wind. The lower-density structures do not trap these fronts, but they can slow …
We use a probabilistic method to compute the propagation of an ionization front corresponding to the re-ionization of the intergalactic medium in a LCDM cosmology, including both hydrogen and helium. The effects of radiative transfer substantially boost the temperature of the ionized gas over the case of uniform re-ionization. The resulting temperature-density relation of the ionized gas is both non-monotonic and multiple-valued, reflecting the non-local character of radiative transfer and suggesting that a single polytropic relation between local gas density and temperatue is a poor descripti…
Motivated by the WMAP results indicating an early epoch of reionization, we consider alternative cosmic star formation models which are capable of reionizing the early intergalactic medium. We develop models which include an early burst of massive stars (with several possible mass ranges) combined with standard star formation. We compute the stellar ionizing flux of photons and we track the nucleosynthetic yields for several elements: D, He4, C, N, O, Si, S, Fe, Zn. We compute the subsequent chemical evolution as a function of redshift, both in the intergalactic medium and in the interstellar …
The temperature of the low-density intergalactic medium is set by the balance between adiabatic cooling resulting from the expansion of the universe, and photo-heating by the UV-background. We have analysed the Lyman-alpha forest of eleven high-resolution quasar spectra using wavelets, and find strong evidence of a marked jump in the temperature at the mean density, T_0, of 60 per cent around a redshift z=3.3, which we attribute to reionization of HeliumII. The jump can be seen in all three of our spectra that straddle redshift 3.3, at a significance of 99 per cent. Below z=3.1, our results ar…
Observational data on the early galactic abundances of the light elements lithium, beryllium and boron are combined with data related to the reionization of the intergalactic medium (IGM) in a search of processes happening in the early universe. Early massive metal-free stars (Pop III), largely held responsible for the reionization of the IGM, are proposed to have been also at the origin of the lithium-6 plateau, through their winds. In this sense the evolution of the Li-6/Be-9 ratio appears to be a key parameter for the history of nucleosynthesis, as a monitor of the early formation of metals…
We derived the evolution of the energy deposition in the intergalactic medium (IGM) by different decaying (or annihilating) dark matter (DM) candidates. Heavy annihilating DM particles (with mass larger than a few GeV) have no influence on reionization and heating, even if we assume that all the energy emitted by annihilations is absorbed by the IGM. In the case of lighter particles, the impact on reionization and heating depends on the efficiency of energy absorption by the IGM. We calculated the fraction of energy produced by decays and annihilations which is effectively absorbed by the IGM.…
The thermal evolution of the intergalactic medium (IGM) depends on the reionization history of the universe. Numerical simulations indicate that the low density IGM, which is responsible for the low column density Ly-alpha forest, follows a well defined temperature-density relation. This results in a cut-off in the distribution of line widths as a function of column density. We use hydrodynamic simulations to calibrate the relation between the cut-off and the temperature-density relation and apply this relation to Keck spectra spanning a redshift range z=2-4.5. We find that the temperature pea…
We examine the possible reionization of the intergalactic medium (IGM) by the source UDF033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep {\it HST}/VLT/{\it Spitzer} images obtained as part of the Great Observatory Origins Deep Survey and {\it Hubble} Ultra-Deep Field projects. Mobasher et al (2005) have identified HUDF-JD2 as a massive ($\sim6\times10^{11}M_\odot$) post-starburst galaxy at redshift z$\gtrsim6.5$. We find that HUDF-JD2 may be capable of reionizing its surrounding region of the Universe, starting the process at a redshift as high as z$\approx 15 \pm5$.
Preliminary results are presented from a simple, single-antenna experiment designed to measure the all-sky radio spectrum between 100 and 200 MHz. The system used an internal comparison-switching scheme to reduce non-smooth instrumental contaminants in the measured spectrum to 75 mK. From the observations, we place an initial upper limit of 450 mK on the relative brightness temperature of the redshifted 21 cm contribution to the spectrum due to neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization, assuming a rapid transition to a fully ionized IGM at a redshift o…
The Lyman alpha absorption from intergalactic, once-ionized helium (HeII) has been measured with HST in four quasars over the last few years, over the redshift range 2.4 < z < 3.2. These observations have indicated that the HeII reionization may not have been completed until z\simeq 2.8, and that large fluctuations in the intensity of the HeII-ionizing background were present before this epoch. The detailed history of HeII reionization at higher redshifts is, however, model-dependent and difficult to determine from these observations, because the IGM can be completely optically thick to Lya ph…
We investigate the role of cosmic rays from young galaxies in heating and ionizing the intergalactic medium (IGM) at high redshift. Using the IRAS observations at $60 μm$, we estimate the cosmic ray luminosity density at the present epoch. We consider various forms of luminosity evolution in redshift and calculate (a) the thresholds corresponding to the upper limits of Gunn-Peterson optical depth, (b) the Compton $y$ parameter for an IGM heated by cosmic rays and compare with the upper limits from COBE measurements and (c) an estimated limit from the integral of metal enrichment. We show that …
