Lukewarm models of the intergalactic medium
Intergalactic medium lukewarm models, considering physical state, cosmic photon spectrum and isothermal and adiabatic expansion
Axford, W. I.↗
SEARCH · Engineering Papers
Results for “intergalactic medium”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Can quasars ionize the intergalactic medium?
The intergalactic environmental impact of quasars is studied in the light of recent QSO observations, addressing in particular whether QSOs can ionize the IGM at z greater than 3.0. After deriving the expansion law for cosmological ionization fronts in a Friedmann universe, it is investigated whether the QSO population is sufficient for these ionized regions to overlap by z of roughly 3.5. The effects of cosmological I-fronts on Lyman-alpha clouds in QSO absorption spectra are discussed.
Donahue, Megan↗
Effects of a hot intergalactic medium
One effect a hot intergalactic medium (IGM) would have would be to produce an isotropic X-ray background through thermal bremsstrahlung. Such a background was modeled including both relativistic electron-ion and electron-electron emission; the observed X-ray measurements could be fit with a current temperature of 10.2 keV and Omega (IGM) of 0.27, assuming that the IGM was instantaneously heated at a redshift of 5 and cools by relativistic adiabatic expansion and Compton cooling. Such a hot IGM would also distort the cosmic microwave background spectrum by inverse Compton scattering off relativistic electrons. This distortion was modeled using the relativistic treatment. When including the recent data of Matsumoto et al., an undistorted radiation temperature of 2.86 K and an Omega (IGM) of 0.41 was found.
Taylor, Gregory B.↗
QSO evolution and the intergalactic medium
A model is developed of a cold, photoionized intergalactic medium in which only discrete, evolving sources (quasars) produce the observed extragalactic hard X-ray background. Constraints on the model are imposed by observed optical depth limits to various redshifts, far UV and visible flux measurements, X-ray background and source counts in the region 2-6 keV, and it makes use of results of the Palomar Bright Quasar Survey and the Braccesi Quasar survey to obtain expressions for the quasar evolution function, absolute luminosity, present number density and switch-on redshift. Results of computer modeling reveal an intergalactic medium with a density with respect to closure less than 0.35, temperature of 16,000 K and fractional ion abundances of approximately 0.000001 for H I and 0.001 for He II, under the assumption of a Hubble constant of 50 km/sec per Mpc. In addition, spectral indices of -0.4 and -1.3 are obtained for the regions of the emission spectrum above and below 4 x 10 to the 18th Hz.
Sherman, R. D.↗
The reionization of the universe: The feedback of galaxy formation on the intergalactic medium
The thermal and ionization evolution of a uniform intergalactic medium (IGM) composed of H and He, undergoing reionization, including the mean effect of gas clumps embedded in a smoothly distributed ambient gas were calculated. The rate equations for ionization and recombination were solved together with the equations of energy conservation, including the effects of cosmological expansion, radiative and Compton cooling, and the diffuse flux emitted by the gas, and radiative transfer. The contribution to the continuum opacity of the universe due to the observed quasar absorption line clouds (QALC'S) were included. A variety of sources of photoionization, including quasars and primeval galaxies, as well as the possibility that hydrodynamical processes deposit thermal energy in the IGM were considered. Applications of these calculations including the evolution of the Ly-alpha forest clouds are described. A self-consistent treatment of the thermal and ionization history of the intergalactic medium (IGM) must take account of the growth of structure in the universe, since the mean density of the IGM corresponds primarily to the time-varying uncollapsed fraction of the baryon-electron component of the matter, and the collapsed fraction, in turn, can have a feedback effect on this uncollapsed fraction by releasing ionizing radiation and thermal energy and by contributing to the opacity of the universe. The coupled evolution of the IGM and the emerging structure with a special focus on the reionization of the IGM, which is believed to have been completed by some redshift z is approximately greater than 4, as inferred from the absence of the Gunn-Peterson effect in the spectra of high z quasars, are studied. The results and implications of detailed, numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He, including the mean effect of an evolving distribution of gas clumps embedded in a smoothly distributed ambient gas is described.
Shapiro, Paul R.↗
The interaction of the gaseous components of galaxies and radio galaxies with an intergalactic medium
Interaction of gaseous components of galaxies and radio galaxies with intergalactic medium
INTERGALACTIC MEDIUM↗
Cosmic far-ultraviolet background radiation - Probe of a dense hot intergalactic medium
Line and continuum radiation fluxes have been computed for a wide range of enriched intergalactic medium (IGM) models. Observations of the diffuse extragalactic light at optical and far-ultraviolet wavelengths are found to provide a potentially important probe of a dense hot intergalactic medium. If the diffuse X-ray background is produced by this gas, the models constrain the cosmological density parameter (Omega) to be less than 0.4. The associated Compton distortions of the cosmic blackbody background radiation and the optical depths to distant quasars at X-ray wavelengths are also evaluated.
Sherman, R. D.↗
A study of galaxy groups and clusters - The case for a clumpy intergalactic medium.
A nonuniform model for a dense intergalactic medium is constructed under the assumption that all groups and clusters of galaxies are gravitationally bound by ionized gas. Catalogs by de Vaucouleurs and Abell are utilized to provide an almost complete sample of the spatial distribution of groups and clusters over a wide range of richness, and a distribution function is derived for galaxy groups and clusters as a function of velocity dispersion. A simple scaling law is applied to predict velocity dispersions for the very rich Abell clusters. Thermal bremsstrahlung emission from the intracluster gas accounts for the observed emission over 2 to 10 keV from several rich clusters, and also contributes up to 20% of the diffuse X-ray background over a considerable fraction of the observed range. The amount of X-ray emitting gas is restricted to a small fraction of the virial mass, with the remainder of the binding mass present as cooler ionized clouds. Available soft X-ray and ultraviolet diffuse background observations are used to define a narrow range of permissible temperatures and densities for these clouds.
Silk, J.↗
A model for the distribution of the intergalactic medium
The evolution and distribution of the intergalactic medium (IGM) in a universe dominated by cold dark matter with Omega(0) = 1 and h = 0.5 are investigated. Galaxies form and eject energy into the IGM from z about 20 up to the present, and the distribution of the IGM is dominated by large connected structures. The power spectrum and two-point correlation function of the IGM show a suppressed growth due to the energy injected from galaxies and the mass subtraction to form galaxies. The high-temperature regions of the IGM correspond to the low-density regions and the low-temperature regions correspond to the high-density regions. The temperature of the IGM increases from z = 1 to z = 0, while the prsssure decreases. The present temperature distribution shows a peak at about 10 million K. The mass fraction of the IGM with temperature below 100,000 K is negligible, indicating almost all the hydrogen is ionized.
Ryu, Dongsu↗
An intergalactic medium temperature from a giant radio galaxy
ABSTRACT The warm–hot intergalactic medium (warm–hot IGM, or WHIM) pervades the filaments of the Cosmic Web and harbours half of the Universe’s baryons. The WHIM’s thermodynamic properties are notoriously hard to measure. Here we estimate a galaxy group–WHIM boundary temperature using a new method. In particular, we use a radio image of the giant radio galaxy (giant RG, or GRG) created by NGC 6185, a massive nearby spiral. We analyse this extraordinary object with a Bayesian 3D lobe model and deduce an equipartition pressure Peq = 6 × 10−16 Pa – among the lowest found in RGs yet. Using an X-ray-based statistical conversion for Fanaroff–Riley II RGs, we find a true lobe pressure $P = 1.5\substack{+1.7\\ -0.4}\times 10^{-15}\ \mathrm{Pa}$. Cosmic Web reconstructions, group catalogues, and MHD simulations furthermore imply an Mpc–scale IGM density $1 + \delta _\mathrm{IGM} = 40\substack{+30\\ -10}$. The buoyantly rising lobes are crushed by the IGM at their inner side, where an approximate balance between IGM and lobe pressure occurs: PIGM ≈ P. The ideal gas law then suggests an IGM temperature $T_\mathrm{IGM} = 11\substack{+12\\-5} \times 10^6\ \mathrm{K}$, or $k_\mathrm{B}T_\mathrm{IGM} = 0.9\substack{+1.0\\-0.4}\ \mathrm{keV}$, at the virial radius – consistent with X-ray-derived temperatures of similarly massive groups. Interestingly, the method is not performing at its limit: in principle, estimates TIGM ∼ 4 × 106 K are already possible – rivalling the lowest X-ray measurements available. The technique’s future scope extends from galaxy group outskirts to the WHIM. In conclusion, we demonstrate that observations of GRGs in Cosmic Web filaments are finally sensitive enough to probe the thermodynamics of galaxy groups and beyond.
79 ASTRONOMY AND ASTROPHYSICS↗
Can quasars photoionize the intergalactic medium at high redshift?
The reionization of the intergalactic medium (IGM) by quasar sources at high redshift are discussed. The integrated UV background from observed QSO's, taking into account the hydrogen opacity associated with intervening Ly-alpha clouds and Lyman limit systems are computed. It is noted that the published data appear to indicate a significant underdensity of absorption systems in the Ly-alpha forest with column densities N(sub HI) greater than 10(exp 15) cm(sup -2). This deficit results in a reduction of the opacity of the universe by a factor of 1.5-3 at z = 3-5 relative to previous estimates. The QSO contribution to the metagalactic flux at the Lyman edge may be as large as J(sub 912)(z) is approximately 6((1 + z)/4.5)(sup 0.5) x 10(exp -22) erg cm(sup -2) s(sup -1) Hz(sup -1) sr(sup -1) for q(sup o) = O, and slightly lower for q(sub o) = 1/2. For a density of the diffuse component of the IGM of omega(sub D)(h(sub 50)(sup 2)) less than 0.025, QSO's could photoionize a smooth IGM sufficiently to satisfy the constraints imposed by the Gunn-Peterson effect. The epoch of reionization could be as recent as z is approximately greater than 5. As a result, neutral patches of IGM would be detectable in the spectra of high redshift quasars. The patches would appear as absorption line systems with typical column densities of 10(exp 19) - 10(exp 20) cm(sup -2), and velocity widths of 100 - 1000 km s(sup -1).
Meiksin, Avery↗
Reionization in a cold dark matter universe: The feedback of galaxy formation on the intergalactic medium
We study the coupled evolution of the intergalactic medium (IGM) and the emerging structure in the universe in the context of the cold dark matter (CDM) model, with a special focus on the consequences of imposing reionization and the Gunn-Peterson constraint as a boundary condition on the model. We have calculated the time-varying density of the IGM by coupling our detailed, numerical calculations of the thermal and ionization balance and radiative transfer in a uniform, spatially averaged IGM of H and He, including the mean opacity of an evolving distribution of gas clumps which correspond to quasar absorption line clouds, to the linearized equations for the growth of density fluctuations in both the gaseous and dark matter components in a CDM universe. We use the linear growth equations to identify the fraction of the gas which must have collapsed out at each epoch, an approach similar in spirit to the so-called Press-Schechter formalism. We identify the IGM density with the uncollapsed baryon fraction. The collapsed fraction is postulated to be a source of energy injection into the IGM, by radiation or bulk hydrodynamical heating (e.g., via shocks) or both, at a rate which is marginally enough to satisfy the Gunn-Peterson constraint at z less than 5. Our results include the following: (1) We find that the IGM in a CDM model must have contained a substantial fraction of the total baryon density of the universe both during and after its reionization epoch. (2) As a result, our previous conclusion that the observed Quasi-Stellar Objects (QSOs) at high redshift are not sufficient to ionize the IGM enough to satisfy the Gunn-Peterson constraint is confirmed. (3) We predict a detectable He II Gunn-Peterson effect at 304(1 + z) A in the spectra of quasars at a range of redshift z greater than or approx. 3, depending on the nature of the sources of IGM reionization. (4) We find, moreover, that a CDM model with high bias parameter b (i.e., b greater than or approx. 2) cannot account for the baryon content of the universe at z approximately 3 observed in quasar absorption line gas unless Omega (sub B) significantly exceeds the maximum value allowed by big bang nucleocynthesis. (5) For a CDM model with bias parameter within the allowed range of (lower) values, the lower limit to Omega(sub B) imposed by big bang nucleosynthesis (Omega(sub B) h(sup 2) greater than or equal to 0.01) combines with our results to yield the minimum IGM density for the CDM fodel. For CDM with b = 1 (Cosmic Background Explorer (COBE) normalization), we find Omega(sub IGM)(sup min) (z approximately 4) approx. equal 0.02-0.03, and Omega(sub IGM)(sup min)(z approximately 0) approx. equal 0.005-0.03, depending upon the nature of the sources of IGM reionization. (6) In general, we find that self-consistent reionization of the IGM by the collapsed baryon fraction has a strong effect on the rate of collapse. (7) As a further example, we show that the feedback effect on the IGM of energy release by the collapsed baryon fraction may explain the slow evolution of the observed comoving QSO number density between z = 5 and z = 2, followed by the sharp decline after z = 2.
Shapiro, Paul R.↗
X-ray constraints on the intergalactic medium
We use ROSAT Position Sensitive Proportional Counter (PSPC) spectra of z approximately equal 3 quasars to constrain the density and temperature of the intergalactic medium (IGM). Strong low-energy cutoffs in PSPC spectra of high-redshift quasars are common. However, the absence of absorption toward some high-redshift quasars can be used to put limits on the possible cosmological density, Omega(sub G), of a hot diffuse intergalactic medium (IGM), via an X-ray Gunn-Peterson test using edge and line opacity in the soft X-rays. The K-edges of oxygen, neon, and carbon and the L-edge of iron produce most of the absorption which is spread out by the redshift of the source. We assume an isotropic, isothermal, nonevolving model of the IGM and calculate the optical depth of this absorption. We find that this test can constrain an enriched IGM at temperatures near 10(exp 5) - 10(exp 6) K, intermediate between the hot IGM ruled out by COBE, and the cold IGM ruled out by the traditional Ly alpha Gunn -Peterson test. Photoionization if the IGM by the ultraviolet and X-ray background has a large effect. We give results for three z approximately equal 3 quasars and discuss how the various trade-offs among temperature, abundance, and backgroud radiation strength affect the limits on Omega (sub G). In addition to the high-redshift case, we discuss techniques for constraining the IGM using X-ray spectra of low-redhift quasars (z approximately equal 0.1 - 0.3). Currently available X-ray spectral data have insufficient energy resolution to constrain the IGM umambiguously, and so expected detection limits for future high-resolution spectrometers are presented. We find that with a large effective area (approximately 2000 sq cm), it is possible to substantially constrain or detect the IGM at the densities which are typically predicted.
Aldcroft, Thomas↗
Evolution of Structure in the Intergalactic Medium and the Nature of the LY-Alpha Forest
We have performed a detailed statistical study of the evolution of structure in a photoionized intergalactic medium (IGM) using analytical simulations to extend the calculation into the mildly nonlinear density regime found to prevail at z = 3. Our work is based on a simple fundamental conjecture: that the probability distribution function of the density of baryonic diffuse matter in the universe is described by a lognormal (LN) random field. The LN distribution has several attractive features and follows plausibly from the assumption of initial linear Gaussian density and velocity fluctuations at arbitrarily early times. Starting with a suitably normalized power spectrum of primordial fluctuations in a universe dominated by cold dark matter (CDM), we compute the behavior of the baryonic matter, which moves slowly toward minima in the dark matter potential on scales larger than the Jeans length. We have computed two models that succeed in matching observations. One is a nonstandard CDM model with OMEGA = 1, h = 0.5, and GAMMA = 0.3, and the other is a low-density flat model with a cosmological constant (LCDM), with OMEGA = 0.4, OMEGA(sub LAMBDA) = 0.6, and h = 0.65. In both models, the variance of the density distribution function grows with time, reaching unity at about z = 4, where the simulation yields spectra that closely resemble the Ly-alpha forest absorption seen in the spectra of high-z quasars. The calculations also successfully predict the observed properties of the Ly-alpha forest clouds and their evolution from z = 4 down to at least z = 2, assuming a constant intensity for the metagalactic UV background over this redshift range. However, in our model the forest is not due to discrete clouds, but rather to fluctuations in a continuous intergalactic medium. At z = 3; typical clouds with measured neutral hydrogen column densities N(sub H I) = 10(exp 13.3), 10(exp 13.5), and 10(exp 11.5) /sq cm correspond to fluctuations with mean total densities approximately 10, 1, and 0.1 times the universal mean baryon density. Perhaps surprisingly, fluctuations whose amplitudes are less than or equal to the mean density still appear as "clouds" because in our model more than 70% of the volume of the IGM at z = 3 is filled with gas at densities below the mean value.
Bi, Hongguang↗
Emergence of the temperature–density relation in the low-density intergalactic medium
We examine the evolution of the phase diagram of the low-density intergalactic medium during the Epoch of Reionization in simulation boxes with varying reionization histories from the Cosmic Reionization on Computers project. The probability density function (PDF) of gas temperature at fixed density exhibits two clear modes: a warm and a cold temperature mode, corresponding to the gas inside and outside of ionized bubbles. We find that the transition between the two modes is ‘universal’ in the sense that its timing is accurately parametrized by the value of the volume-weighted neutral fraction for any reionization history. This ‘universality’ is more complex than just a reflection of the fact that ionized gas is warm and neutral gas is cold: it holds for the transition at a fixed value of gas density, and gas at different densities transitions from the cold to the warm mode at different values of the neutral fraction, reflecting a non-trivial relationship between the ionization history and the evolving gas density PDF. Furthermore, the ‘emergence’ of the tight temperature–density relation in the warm mode is also approximately ‘universally’ controlled by the volume-weighted neutral fraction for any reionization history. In particular, the ‘emergence’ of the temperature–density relation (as quantified by the rapid decrease in its width) occurs when the neutral fraction is 10 –4 ≲ X HI ≲ 10 –3 for any reionization history. Our results indicate that the neutral fraction is a primary quantity controlling the various properties of the temperature–density relation, regardless of reionization history.
79 ASTRONOMY AND ASTROPHYSICS↗
Galaxy formation in an intergalactic medium dominated by explosions
The evolution of galaxies in an intergalactic medium dominated by explosions of star systems is considered analogously to star formation by nonlinearly interacting processes in the interstellar medium. Conditions for the existence of a hydrodynamic instability by which galaxy formation leads to more galaxy formation due to the propagation of the energy released at the death of massive stars are examined, and it is shown that such an explosive amplification is possible at redshifts less than about 5 and stellar system masses between 10 to the 8th and 10 to the 12th solar masses. Explosions before a redshift of about 5 are found to lead primarily to the formation of massive stars rather than galaxies, while those at a redshift close to 5 will result in objects of normal galactic scale. The model also predicts a dusty interstellar medium preventing the detection of objects of redshift greater than 3, numbers and luminosities of protogalaxies comparable to present observations, unvirialized groups of galaxies lying on two-dimensional surfaces, and a significant number of black holes in the mass range 1000-10,000 solar masses.
Ostriker, J. P.↗
The fraction of ionizing radiation from massive stars that escapes to the intergalactic medium
Whether stars could have driven the reionization of the intergalactic medium depends critically on the proportion of ionizing radiation that escapes the galaxies in which it is produced. Spectroscopy of gamma-ray burst (GRB) afterglows can be used to estimate the opacity to extreme ultraviolet (EUV) radiation along the lines-of-sight to the bursts. Assuming that long-duration GRBs trace the locations of the massive stars dominating EUV production, the average escape fraction of ionizing radiation can be calculated independently of galaxy size or luminosity. Here we present a compilation of HI column density (N(HI)) measures for 140 GRBs in the range 1.6 < z <6.7. Although the sample is heterogeneous, in terms of spectral resolution and signal-to-noise ratio, fits to the Ly α absorption line provide robust constraints on N(HI), even for spectra of insufficient quality for other purposes. Thus we establish an escape fraction at the Lyman limit of {f(esc)} ≈ 0.005, with a 98 per cent confidence upper limit of {f(esc)} ≈ 0.015. This analysis suggests that stars provide a small contribution to the ionizing radiation budget at z < 5. At higher redshifts firm conclusions are limited by the small size of the GRB sample (7/140), but any decline in average HI column density seems to be modest. We also find no significant correlation of N(HI) with galaxy UV luminosity or host stellar mass. We discuss in some detail potential biases and argue that, while not negligible, systematic errors in f(esc) are unlikely to be more than a factor ∼2 in either direction, and so would not affect the primary conclusions. Given that many GRB hosts are low-metallicity dwarf galaxies with high specific star-formation rates, these results present a particular problem for the hypothesis that such galaxies dominated the reionization of the Universe.
N R Tanvir↗
Measurements of the thermal and ionization state of the intergalactic medium during the cosmic afternoon
We perform the first measurement of the thermal and ionization state of the intergalactic medium (IGM) across 0.9 < z < 1.5 using 301 Ly α absorption lines fitted from 12 archival Hubble Space Telescope Space Telescope Imaging Spectrograph quasar spectra. We employ the machine-learning-based inference method that uses joint Doppler parameter–column density (b-N HI ) distributions obtained from Ly α forest decomposition. Our results show that the Γ HI photoionization rates, , agree with recent ultraviolet background synthesis models, with log(Γ HI /s -1 ) = $-11.79^{+0.18}_{-0.15}$, $-11.98^{+0.09}_{-0.09}$, and $-12.32^{+0.10}_{-0.12}$, at z = 1.4, 1.2, and 1, respectively. We obtain the IGM temperature at the mean density, T 0 , and the adiabatic index, γ, as [log(T 0 /K), γ] = $[4.13^{+0.12}_{-0.10}, 1.34^{+0.10}_{-0.15}]$, $[3.79^{+0.11}_{-0.11}, 1.70^{+0.09}_{-0.09}]$, and $[4.12^{+0.15}_{-0.25}, 1.34^{+0.21}_{-0.26}]$ at z = 1.4, 1.2, and 1. Our measurements of T 0 at z = 1.4 and 1.2 are consistent with the trend predicted from previous z < 3 temperature measurements and theoretical expectations, where the IGM cools down after $He\tiny{II}$ reionization in the absence of any non-standard heating. However, our T 0 measurement at z = 1 unexpectedly high IGM temperature. Given the relatively large uncertainty in these measurements, where σ T$_0$ ~ 5000 K, mostly emanating from the limited size of our data set, we cannot conclude whether the IGM cools down as expected. Lastly, we generate mock data sets to test the constraining power of future measurement with larger data sets. The results demonstrate that, with redshift path-length Δz ~ 2 for each redshift bin, three times the current data set, we can constrain the T 0 of IGM within 1500 K, which would be sufficient to constrain the IGM thermal history at z < 1.5 conclusively.
79 ASTRONOMY AND ASTROPHYSICS↗