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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2

All sources NASA NTRS DOE OSTI

NASA NTRS1981

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.↗

NASA NTRS2018

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↗

DOE OSTI2024

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↗

DOE OSTI2017

Preheating of the Intergalactic Medium by Gravitational Collapse and Ultraviolet Background

The preheating of the intergalactic medium by structure collapse and ultraviolet background (UVB) is investigated in cosmological hydrodynamical simulations. When gravitational collapse is the sole heating mechanism, we find that (1) 60% and 45% of the IGM are heated up to S > 8 and 17 keV cm{sup 2}, respectively, at z = 0, but the fractions drop rapidly to a few percent at z = 2; (2) the entropy of the circumhalo gas S{sub cir} is higher than the virial entropy for more than 75% of the halos with masses M<10{sup 11.5} M{sub ⊙} since z = 2, but the fraction higher than the entropy, S{sub pr}, required in the preventive model of galaxy formation is only 15%–20% for halos with M<10{sup 10.5} M{sub ⊙} at z = 0, and decreases as redshift increases; (3) assuming a metallicity of Z⩽0.03 Z{sub ⊙}, the fraction of halos whose circumhalo gas has a cooling time longer than the Hubble time t{sub cool,cir}>t{sub H} is merely 5%–10% at z≲0.5, and even less at z⩾1 for halos with M<10{sup 10.5} M{sub ⊙}; and (4) gas in the filaments undergoes the strongest preheating. Furthermore, we show that the UVB cannot enhance the fraction of the IGM with S>17 keV cm{sup 2}, but can increase the fraction of low-mass halos (<10{sup 10.5} M{sub ⊙}) having S{sub cir}>S{sub pr} to ∼70% at z = 0 and that having t{sub cool,cir}>t{sub H} to 15%–30% at z≲0.5. Our results indicate that preheating due to gravitational collapse and UVB is inadequate to fulfill the needs of the preventative model, especially for halos with 10{sup 10.5} M{sub ⊙}<M<10{sup 11.5} M{sub ⊙}. Nevertheless, these two mechanisms might cause large-scale galactic conformity.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

PAPER-64 CONSTRAINTS ON REIONIZATION. II. THE TEMPERATURE OF THE z = 8.4 INTERGALACTIC MEDIUM

We present constraints on both the kinetic temperature of the intergalactic medium (IGM) at z = 8.4, and on models for heating the IGM at high-redshift with X-ray emission from the first collapsed objects. These constraints are derived using a semi-analytic method to explore the new measurements of the 21 cm power spectrum from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), which were presented in a companion paper, Ali et al. Twenty-one cm power spectra with amplitudes of hundreds of mK{sup 2} can be generically produced if the kinetic temperature of the IGM is significantly below the temperature of the cosmic microwave background (CMB); as such, the new results from PAPER place lower limits on the IGM temperature at z = 8.4. Allowing for the unknown ionization state of the IGM, our measurements find the IGM temperature to be above ≈5 K for neutral fractions between 10% and 85%, above ≈7 K for neutral fractions between 15% and 80%, or above ≈10 K for neutral fractions between 30% and 70%. We also calculate the heating of the IGM that would be provided by the observed high redshift galaxy population, and find that for most models, these galaxies are sufficient to bring the IGM temperature above our lower limits. However, there are significant ranges of parameter space that could produce a signal ruled out by the PAPER measurements; models with a steep drop-off in the star formation rate density at high redshifts or with relatively low values for the X-ray to star formation rate efficiency of high redshift galaxies are generally disfavored. The PAPER measurements are consistent with (but do not constrain) a hydrogen spin temperature above the CMB temperature, a situation which we find to be generally predicted if galaxies fainter than the current detection limits of optical/NIR surveys are included in calculations of X-ray heating.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1989

The intergalactic medium and galaxy formation

Recent observational and theoretical investigations of the intergalactic medium (IGM), defined as the component of the baryon-electron matter which now occupies the space between galaxies and which filled the pregalactic universe, are reviewed. Topics addressed include the Gunn-Peterson constraint on the history of the IGM, the mean mass density of the IGM at high redshift, requirements for ionizing the IGM, the observed quasar contribution, the thermal and ionization history of the IGM (quasar photoionization, stellar sources of the ionizing background, and alternative sources such as protogalactic shock radiation and the decay of exotic particles), and the hydrodynamical evolution of the IGM. Typical results from observations and numerical simulations are presented graphically.

Shapiro, Paul R.↗

NASA NTRS2022

CLEAR: Boosted Lyα Transmission of the Intergalactic Medium in UV-bright Galaxies

Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Lyα studies during the epoch of reionization show evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Lyα from these galaxies. We investigate this problem using IR slitless spectroscopy from the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) G102 grism observations of 148 galaxies selected via photometric redshifts at 6.0 < z < 8.2. These galaxies have spectra extracted from the CANDELS Lyα Emission at Reionization (CLEAR) survey. We combine the CLEAR data for 275 galaxies with the Keck Deep Imaging Multi-Object Spectrograph and MOSFIRE data set from the Texas Spectroscopic Search for Lyα Emission at the End of Reionization Survey. We constrain the Lyα equivalent width (EW) distribution at 6.0 < z < 8.2, which is described by an exponential form, dN / dEW ∝ exp(-EW) W(sub 0), with the characteristic e-folding scale width (W(sub 0)). We confirm a significant drop in the Lyα strength (i.e., W(sub 0)) at z > 6. Furthermore, we compare the redshift evolution of W(sub 0) between galaxies at different UV luminosities. UV-bright (M(sub UV) < −21 [i.e., L(sub UV) > L*]) galaxies show weaker evolution with a decrease of 0.4 ( ± 0.2) dex in W(sub 0) at z > 6, while UV-faint (M(sub UV) > −21 [LUV < L*]) galaxies exhibit a significant drop of 0.7–0.8 (±0.2) dex in W(sub 0) from z < 6 to z > 6. If the change in W(sub 0) is proportional to the change in the IGM transmission for Lyα photons, then this is evidence that the transmission is “boosted” around UV-brighter galaxies, suggesting that reionization proceeds faster in regions around such galaxies.

Reionization↗

NASA NTRS2000

X-Ray Constraints on the Warm-Hot Intergalactic Medium

Three observational constraints can be placed on a warm-hot intergalactic medium (WHIM) using ROSAT Position Sensitive Proportional Counter (PSPC) pointed and survey data, the emission strength, the energy spectrum, and the fluctuation spectrum. The upper limit to the emission strength of the WHIM is 7.5 +/- 1.0 keV/(s*sq cm*sr*keV) in the 3/4 keV band, an unknown portion of which value may be due to our own Galactic halo. The spectral stape of the WHIM emission can be described as thermal emission with logT = 6.42, although the true spectrum is more likely to come from a range of temperatures. The values of emission strength and spectral shape are in reasonable agreement with hydrodynamical cosmological models. The autocorrelation function in the 0.44 keV < E < 1.21 keV band range, w(theta), for the extragalactic soft X-ray background (SXRB) which includes both the WHIM and contributions due to point sources, is approx. < 0.002 for 10 min < 0 < 20 min in the 3/4 keV band. This value is lower than the Croft et al. (2000) cosmological model by a factor of approx. 5, but is still not inconsistent with cosmological models. It is also found that the normalization of the extragalactic power law component of the soft X-ray background spectrum must be 9.5 +/- 0.9 keV/(s*sq cm*sr*keV) to be consistent with the ROSAT All-Sky Survey.

Kuntz, K. D.↗

NASA NTRS1979

Distortion of the microwave background by a hot intergalactic medium

The distortion of the cosmic microwave background by a hot, optically thin intergalactic medium (IGM) is calculated using the full frequency redistribution function. Even if the IGM produces all of the cosmic X-ray background, the distortion of the microwave background is not detectable in the present observational data.

Wright, E. L.↗

NASA NTRS1991

Diagnosing the reionization of the universe - The absorption spectrum of the intergalactic medium and Lyman alpha clouds

The thermal and ionization evolution of a uniform intergalactic medium composed of H and He and undergoing reionization is studied. The diagnosis of the metagalactic ionizing radiation background at z of about three using metal line ratios for Lyman limit quasar absorption line systems is addressed. The use of the He II Gunn-Peterson effect to diagnose the reionization source and/or nature of the Hy-alpha forest clouds is considered.

Giroux, Mark L.↗

NASA NTRS1984

Reheating the intergalactic medium under extremal conditions

Sherman (1982) commenced the investigation of a hypothetical closure density intergalactic medium (IGM) in the recombination epoch and found present acceptable temperatures in the range from 160,000 to 4,200,000 K for IGM heating. The present investigation has the objective to complete these calculations by finding extreme bounds on the reheating epoch which preceded recombination. The final results are presented in a table. Three models have been generated. The presented models suggest that a closure density IGM is constrained to be heated by a source in the range from 10 to the -31st to 10 to the -27th ergs per s per cu cm. The heating had to originate no earlier than z approximately 28.

Sherman, R. D.↗

DOE OSTI2020

Effective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis

We measure the effective opacity (τ{sub eff}) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2 ≲ z ≲ 3. Our spectra are taken from the COSMOS Lyα Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Lyα forest, we measure the effective Lyα opacity (τ{sub eff}) in the 2.02 ≤ z ≤ 2.44 range. At z = 2.22, we estimate τ{sub eff} =0.159±0.001 from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z < 2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous τ{sub eff} measurements that describes the steep redshift evolution in τ{sub eff} from z = 1.5–4.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Inferring the Thermal History of the Intergalactic Medium from the Properties of the Hydrogen and Helium Lyα Forest

The filamentary network of intergalactic medium (IGM) gas that gives origin to the Lyα forest in the spectra of distant quasars encodes information on the physics of structure formation and the early thermodynamics of diffuse baryonic material. Here we use a massive suite of more than 400 high-resolution cosmological hydrodynamical simulations run with the Graphics Processing Unit–accelerated code Cholla to study the IGM at high spatial resolution maintained over the entire computational volume. The simulations capture a wide range of possible IGM thermal histories by varying the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei. A statistical comparison of synthetic spectra with the observed 1D flux power spectra of hydrogen at redshifts 2.2 ≤ z ≤ 5.0 and with the helium Lyα opacity at redshifts 2.4 < z < 2.9 tightly constrains the photoionization and photoheating history of the IGM. By leveraging the constraining power of the available Lyα forest data to break model degeneracies, we find that the IGM experienced two main reheating events over 1.2 Gyr of cosmic time. For our best-fit model, hydrogen reionization completes by z R ≈ 6.0 with a first IGM temperature peak of T 0 ≃ 1.3 × 10 4 K and is followed by the reionization of He ii that completes by z R ≈ 3.0 and yields a second temperature peak of T 0 ≃ 1.4 × 10 4 K. We discuss how our results can be used to obtain information on the timing and the sources of hydrogen and helium reionization.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1988

The distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter dominated universe

The evolution and distribution of galaxies and the intergalactic medium (IGM) have been studied, along with collisionless dark matter in a Universe dominated by cold dark matter. The Einstein-deSitter universe with omega sub 0 = 1 and h = 0.5 was considered (here h = H sub 0 bar 100/kms/Mpc and H sub 0 is the present value of the Hubble constant). It is assumed that initially dark matter composes 90 pct and baryonic matter composes 10 pct of total mass, and that the primordial baryonic matter is comprised of H and He, with the abundance of He equal to 10 pct of H by number. Galaxies are allowed to form out of the IGM, if the total density and baryonic density satisfy an overdensity criterion. Subsequently, the newly formed galaxies release 10 to the 60th ergs of energy into the IGM over a period of 10 to the 8th years. Calculations have been performed with 32 to the 3rd dark matter particles and 32 to the 3rd cells in a cube with comoving side length L = 9.6/h Mpc. Dark matter particles and galaxies have been followed with an N-body code, while the IGM has been followed with a fluid code.

Ryu, Dongsu↗

NASA NTRS2003

The Ionization History of The Intergalactic Medium:

The funded project seeked a unified description of the ionization, physical structure, and evolution of the intergalactic medium (IGM) and quasar intervening absorption systems. We proposed to conduct theoretical studies of the IGM and QSO absorbers in the context of current theories of galaxy formation, developing and using numerical and analytical techniques aimed at a detailed modeling of cosmological radiative transfer, gas dynamics, and thermal and ionization evolution. The ionization history of the IGM has important implications for the metagalactic UV background, intergalactic helium absorption 21-cm tomography, metal absorption systems, fluctuations in the microwave background, and the cosmic rate of structure and star formation. All the original objectives of our program have been achieved, and the results widely used and quoted by the community. Indeed, they remain relevant as the level and complexity of research in this area has increased substantially since our proposal was submitted, due to new discoveries on galaxy formation and evolution, a flood of high-quality data on the distant universe, new theoretical ideas and direct numerical simulations of structure formation in hierarchical clustering theories.

Madau, Piero↗

DOE OSTI2016

ON THE BEAM INDUCED QUASI-INSTABILITY TRANSFORMATION OF THE DAMPED APERIODIC MODE IN THE INTERGALACTIC MEDIUM

Highly relativistic electron–positron pair beams considerably affect the spontaneously emitted field fluctuations in the unmagnetized intergalactic medium (IGM). In view of the considered small density ratio of beam and background plasma, a perturbative treatment is employed in order to derive the spectral balance equations for the fluctuating fields from first principles of plasma kinetic theory that are covariantly correct within the limits of special relativity. They self-consistently account for the competing effects of spontaneous and induced emission and absorption in the perturbed thermal plasma. It is found that the presence of the beam transforms the growth rate of the dominating transverse damped aperiodic mode into an effective growth rate that displays positive values in certain spectral regions if beam velocity and wave vector are perpendicular or almost perpendicular to each other. This corresponds to a quasi-instability that induces an amplification of the fluctuations for these wavenumbers. Such an effect can greatly influence the cosmic magnetogenesis as it affects the strengths of the spontaneously emitted magnetic seed fields in the IGM, thereby possibly lowering the required growth time and effectivity of any further amplification mechanism such as an astrophysical dynamo.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1991

The evolving intergalactic medium - The uncollapsed baryon fraction in a cold dark matter universe

The time-varying density of the intergalactic medium (IGM) is calculated by coupling detailed numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He to the linearized equations for the growth of density fluctuations in both gases and a dark component in a cold dark matter universe. The IGM density is identified with the collapsed baryon fraction. It is found that even if the IGM is never reheated, a significant fraction of the baryons remain uncollapsed at redshifts of four. If instead the collapsed fraction releases enough ionizing radiation or thermal energy to reionize the IGM by z greater than four as required by the Gunn-Peterson (GP) constraint, the uncollapsed fraction at z of four is even higher. The known quasar distribution is insufficient to supply the ionizing radiation necessary to satisfy the GP constraint in this case and, if stars are instead responsible, a substantial metallicity must have been produced by z of four.

Shapiro, Paul R.↗

NASA NTRS2020

Bubble Mapping with the Square Kilometre Array - I. Detecting Galaxies with Euclid, JWST, WFIRST, and ELT within Ionized Bubbles in the Intergalactic medium at z > 6

The Square Kilometre Array (SKA) is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z > 6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centred on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z ≈ 7–10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at z ≤ 10. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST, or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z ≈ 10, due to the very small number of line-of-sight interlopers expected at these redshifts.

Erik Zackrisson↗