Intergalactic Hydrogen Research Articles

Measurement of the opacity of ionized helium in the intergalactic medium

DETERMINATION of the density and ionization state of diffuse primordial gas in the intergalactic medium (IGM) is an important step towards understanding the nature of dark matter and the formation of structure in the Universe. Absorption by neutral hydrogen atoms in the IGM should produce a large flux deficit in the spectra of high-redshift quasars at wavelengths below that of the H I Lyman-α line (the Gunn–Peterson effect1). But observations of quasars at low spectral resolution have revealed only relatively small deficits, and at higher spectral resolution these appear as numerous discrete absorption features (the Lyman-α forest). This implies that intergalactic hydrogen is both highly ionized and non-uniformly distributed2. Similar absorption is expected from intergalactic helium3, although its detection is more challenging and evidence for its existence was obtained only recently4,5. Here we report the observation of absorption from singly ionized helium (He ii) in the spectrum of the quasar HS1700 + 64. We measure a mean flux deficit over the redshift range 2.2 < z < 2.6 that yields an effective optical depth of 1.00 (±0.07). Comparing this result with the H I absorption towards this quasar, we argue that most of the measured He II absorption occurs in the lowest-density regions of the IGM.

Contribution of Bremsstrahlung Emission from Lyα Clouds to the Microwave Background Fluctuations

I calculate the contribution of bremsstrahlung emission from Lyα absorption clouds to the brightness of the microwave sky. The calculation is based only on the assumption that the clouds below the Lyman limit are in photoionization equilibrium with a UV background radiation and avoids any uncertainty about the clumpiness of the gas. I predict a minimum fluctuation amplitude in the Rayleigh-Jeans regime of ΔT/T = 10-5.5±0.4 J221 1/2 (λ/5 cm)2, which varies over characteristic angular scales ~1''-100'', where λ is the observed wavelength and J221 1/2 is a weighted redshift average of the UV background intensity at the Lyman limit in units of 10-21 ergs cm-2 s-1 Hz-1 sr-1. Detection of this signal can be used to map the intergalactic hydrogen distribution and to calibrate the UV background at high redshifts. Existing VLA observations constrain J221 1/2 101.3±0.4, unless some of the extended flat-spectrum sources that were detected are Lyα absorption systems.

Low Surface Brightness Hα Observations of Local Intergalactic Hydrogen Clouds

We present upper limits on the local ionizing background based on a search for extended Hα emission from three nearby intergalactic H I clouds: the Leo Ring (M96 group), both the NE and SW lobes of the Haynes-Giovanelli Virgo Cloud (H I 1225+01), and the H I tidal tails associated with the NGC 4631/4656 group. These clouds were chosen to have 21 cm emission that is extended (10-100 kpc) and distant from any associated galaxy. Deep, wide-field CCD images were acquired through narrow- (~31 A) and broadband R filters with the Burrell Schmidt telescope on Kitt Peak. We set a 95% confidence upper limit on the Hα surface brightness for the areas of the clouds detected in H I of 1.6 × 10-19 ergs s-1 cm-2 arcsec-2 in Leo and of 3.7 × 10-19 ergs s-1 cm-2 arcsec-2 in Virgo. We limit the local ionizing background to Φ0 < 5.0 × 103 photons s-1 cm-2 sr-1 (95%) at the location of the Leo Ring cloud and Φ0 < 1.1 × 104 photons s-1 cm-2 sr-1 at the Virgo cloud, assuming spherical clouds. (Limits are a factor of 2 higher for a thin face-on slab.) The limits correspond to J0 < 3.3 × 10-23 and 7.6 × 10-23 ergs s-1 cm-2 sr-1 Hz-1 for a ν-1/2 spectrum (1.6 times higher for a ν-1.4 spectrum) between 1 and 4 ryd. Such low limits suggest that quasar light, and not galactic light, dominates the ionizing background at low redshift. The Hα limit on the Leo cloud is significantly below a previously reported detection. In the field of the edge-on galaxies NGC 4631 and NGC 4656, we detect Hα from ionized gas extending nearly 16 kpc above N4631, which could have been blown out by starburst activity in the plane, and a low surface brightness companion or stellar tidal tail. This companion lies between N4631's H I tidal tails and may have played a role in creating the H I tidal tails, or it may represent star formation within the tidal tails. We also report the tentative detection of an ultrafaint sheet of Hα emission extending from NGC 4631 to NGC 4656.

Cosmic neutrino radiation in the far ultraviolet and the E 6 model

Observations of the cosmic ultraviolet background by the Berkeley UVX spectrometer sets an upper limit to the intensity of radiation due to possibly existing radiatively decaying primordial particles in the mass range 13.5–17.5 eV. If such particles exist with a number density equalling that of neutrinos today they must have a lifetime exceeding 4.6×10 23s. We explore the idea of Sciama that tau neutrinos ν τ of mass 29±1 eV with a lifetime of (2±1)×10 23 s decay radiatively into α μ or α e thereby being responsible for the ionization of interstellar and intergalactic hydrogen (the Gunn-Petersen effect). In the standard model this is impossible; however, in the context of an E 6 model the neutrinos may have radiative lifetimes of the order of 10 10 3 s.

The evolution of intergalactic Hydrogen clouds: confusion resolved

It is now widely accepted that a population of intergalactic hydrogen clouds is responsible for the plethora of absorption lines seen at wavelengths shorter than Ly α emission in all high-z QSOs. The question of whether the comoving number density of such clouds evolves with redshift has been somewhat controversial. It is usually assumed that

Absorption spectrum of the z=3.78 QSO 2000-330 at high resolution

The forest of absorption lines observed in all high-redshift QSOs at wavelengths shorter than Ly α emission is generally accepted as being due to a population of intergalactic hydrogen clouds. In order to study the physical properties of these clouds and possible changes in the properties with redshift it is first necessary to establish the true continuum level. The difficulty in defining continuum levels in the Ly α forest region is readily acknowledged in the literature but only rarely do published spectra show the adopted continuum.

Limits on the infrared and visual luminosity of the intergalactic H I cloud in Leo

Low surface brightness photometry of the intergalactic neutral hydrogen cloud in Leo sets upper limits on the intensity of this object of 28.0 mag/sq arcsec in the V photometric band and 22.8 mag/sq arcsec in the K band. The corresponding ratio of the H I mass to blue luminosity in the H I emission peaks of the cloud must be greater than 2.9 (solar units) depending on the star formation history of the object. The limits imposed on the star formation rate suggest a strong dependence of this rate on gas density.

Signs of First Intergalactic Hydrogen Cloud Spotted

Signs of First Intergalactic Hydrogen Cloud Spotted

A statistical study of the Lyman-Alpha absorption lines of nine quasars

We investigate the properties of the L α absorption lines in the high resolution spectra of nine quasars, B2 1225+31.7, PKS 2126-158, Q 0002-422, Q 1453-423, PHL 957, PKS 0528-250, PKS 0805+046, PKS 1448-232 and PKS 1442+101. Their emission line redshift range is 2.20 ⩽ z em ⩽ 3.54; a total of 350 L α absorption lines cover the range 1.70 ⩽ z abs ⩽ 3.54. Our analysis support the following conclusions; 1) the number density of L α absorption lines is not significantly different in different quasars. 2) The number density does not vary significantly with redshift. 3) Their equivalent width spectrum does not vary significantly with redshift. 4) Their properties are the same whether in the wing of the L α emission or in the continuum. 5) Their two-point correlation function is flat within the limit of resolution, which is different from the behaviour of galaxies. These results show that the L α absorption lines in high-redshift quasars are very probably produced by intergalactic hydrogen clouds uniformly distributed throughout space.

Upper Limits on the Space Density of Intergalactic Neutral Hydrogen Clouds

A survey in the 21 cm line of H I of 153 square degrees of sky out in a distance corresponding to 3000 km s/sup -1/ and with a limiting sensitivity of 3 x 10/sup 6/D/sup 2/ M/sub sun/ has failed to turn up any convincing detections that are unassociated with a visible counterpart. These results, combined with previous limits, lead to the conclusion that the mass in intergalactic H I clouds in the interval 10/sup 7/ M/sub circle-solid/ to 10/sup 10/ M/sub sun/ is less than 6% of the mass in galaxies and less than 5 x 10/sup -4/ times the density required for a closed universe (assuming H/sub 0/ = 100 km s/sup -1/ Mpc/sup -1/).

A search for intergalactic hydrogen clouds in the vicinity of nearby dwarf galaxies

A search for intergalactic hydrogen clouds in the vicinity of nearby dwarf galaxies

Are there really intergalactic hydrogen clouds in the Sculptor group

High-sensitivity 21 cm observations of the region of the Sculptor group of galaxies reveal at least 30 H I clouds distributed over only the southern sector of the group. These new data add two striking complications to the picture of the clouds as H I companions of Sculptor galaxies: first, a much wider spatial distribution of clouds in marked contrast with the clustering of clouds around NGC 55 and NGC 300 previously reported by Mathewson, Cleary, and Murray; and second, a cloud velocity distribution which does not match that of the galaxies.We cannot reconcile the spatial and velocity distributions of the H I clouds with those of the group or of any subgroup. We conclude that there are no intergalactic H I clouds of > or =10/sup 8/ M/sub sun/ and galactic dimensions within the Sculptor group. Of a number of explanations alternative to group membership, we favor the identification of the clouds as a component of the Magellanic Stream which is seen in projection. Observations reported here of other nearby groups, combined with those of Sculptor, rule out the existence of a significant population of discrete H I clouds having the above properties.

Cosmic-ray nucleosynthesis and the infall rate of extragalactic matter in the solar neighborhood

We present an up-to-date discussion of the galactic abundances of lithium, beryllium, and boron, and show that new insights into a number of astrophysical problems arise from recent improvements in the quantity and quality of the data.The observed galactic abundances of these elements remain surprisingly constant in time, at values significantly lower than predictions made by conventional models of closed galactic evolution. This fact suggests that intergalactic hydrogen may enter our neighborhood. We favor a local infall rate of about 2 M/sub sun/ per 10/sup 9/ years per pc/sup 2/, and discuss the rather large uncertainties on this rate.The measured ratios of element and isotope abundances among the light elements suggest that the average energy spectrum of fast particles in our galactic neighborhood turns up below 50--100 MeV per nucleon. Such a turnup implies that two source families for cosmic rays must exist, perhaps supernovae and ordinary stars.In carbonaceous chondrites, not only boron, but apparently also beryllium and perhaps even lithium, seem to be enriched beyond their stellar abundance values.And even after many years of study, the origin of /sup 7/Li remains uncertain.

QSO absorption lines and intergalactic hydrogen clouds

The absorption line spectra of some QSOs are similar to the absorption line spectra imposed by the interstellar medium in our own galaxy on the spectra of hot stars (see Figure 1). the spectra of other QSOs show P Cygni profiles similar to those of hot stars with mass outflow (see Figure 2). the absorption lines in both of these types of spectra are due to the resonant transitions of hydrogen and of the more abundant elements.

On the possible existence of cosmological cosmic rays. I - The framework for light-element and gamma-ray production

view Abstract Citations (21) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the possible existence of cosmological cosmic rays. I. The framework for light-element and gamma-ray production. Montmerle, T. Abstract The possible existence of cosmological cosmic rays (CCR) is considered in the context of an expanding universe. A model accounting for CCR production, composition and spectrum is given. This version assumes that CCR were formed in a burst (Stecker, 1971) at some starting redshift. CCR are interpreted as consisting of protons and alpha particles only; the high-energy sector of the CCR spectrum produces pi-mesons (and thence gamma rays) by collision with matter, while the low-energy sector collides with intergalactic hydrogen, heating the ambient and ionizing the gaseous component. Also, light element production involving alpha-alpha reactions that give rise to isotopes of elements such as lithium is assumed to take place. Cosmological parameters and transport equations for photons as well as for nuclei are discussed; the relevant source functions are also studied, and analytical solutions to the transport equations are derived. Procedures for obtaining quantitative results for the CCR alpha-particle flux are given, as well as methods for determining the gamma ray background spectrum and accounting for an abundance of the isotope Li-7. Publication: The Astrophysical Journal Pub Date: August 1977 DOI: 10.1086/155459 Bibcode: 1977ApJ...216..177M Keywords: Abundance; Astronomical Models; Cosmic Rays; Cosmology; Gamma Rays; Light Elements; Alpha Particles; Astrodynamics; High Energy Interactions; Hydrogen Clouds; Intergalactic Media; Lithium Isotopes; Nuclear Fusion; Universe; Astrophysics full text sources ADS |

Radio-frequency limits to the abundance of intergalactic neutral hydrogen

view Abstract Citations (5) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio-frequency limits to the abundance of intergalactic neutral hydrogen. Lang, K. R. Abstract Radio-frequency spectra were obtained in order to search for neutral hydrogen in or along the line of sight to the radio galaxies 3C 264, 3C 270, 3C 272.1, and 3C 296. New limits to the volume density of intergalactic neutral hydrogen were obtained. The respective upper limits for the four sources are 2.6 millionths per cu cm, 92 millionths per cu cm, 56 millionths per cu cm, and 1.7 millionths per cu cm. The upper limits are considered to be at better than the 90-per cent confidence level. Because the number density of neutral hydrogen needed to close the Universe is 2 millionths per cu cm, these observations provide additional support for the conclusion that there is insufficient intergalactic hydrogen to stop the expansion of the Universe. Publication: The Astrophysical Journal Pub Date: June 1976 DOI: 10.1086/182140 Bibcode: 1976ApJ...206L..91L Keywords: Abundance; Hydrogen; Intergalactic Media; Radio Spectra; Big Bang Cosmology; Frequency Response; Gas Density; Mass Distribution; Radio Sources (Astronomy); Astrophysics full text sources ADS |

Theoretical Models of Photoionized Intergalactic Hydrogen

The effects of ionizing radiation emitted by quasi-stellar objects on intergalactic hydrogen are studied. The hydrogen is assumed to expand with the Universe, and the amount of ionizing radiation is estimated from observations of the QSO luminosity function. The discreteness of the radiation sources is taken into account in computing the thermal history of the medium. The amount of ionizing radiation is shown to be sufficient to allow the existence of a universal medium with a temperature less than 10,000 K and a density several times the smeared-out density of luminous matter in galaxies. Such a medium would escape detection with presently available techniques.

New Limits on the Shear and Rotation of the Universe from the X-ray Background

It is shown that recently set upper limits of 1 percent on 12- and 24hour angular variations in the X-ray background radiation lead to restrictions on large-scale shear and vorticity for approximately haff of the sky. Because of a global analogy to the Compton-Getting effect, the limiting values placed on the shear and vorticity are of the same order as those set by the isotropy of the microwave background (over a small solid angle) if intergalactic hydrogen now exists at densities &gt;106 for the shear model, and &gt; 10 for the vorticity model. If intergalactic hydrogen does not exist, the limits are not as significant as those implied by the microwave background, but are still important because of the large solid angle scanned in the observations. A "Euclidean," axisymmetric world model with shear, and two models containing vorticity and having open and closed geometries, are used in the calculations.

Quasi-Stellar Objects and the Density of Intergalactic Hydrogen

Quasars and intergalactic hydrogen density, using Schmidt law of increase in number density of quasars to construct plausible models

Intergalactic HYdrogen in the Virgo Cluster of Galaxies

THE first clear positive evidence for the existence of inter-galactic atomic neutral hydrogen was advanced in 1966 by Koehler and Robinson1 from absorption effects in the continuum radio spectra of Fornax A, 3(C 273, and Virgo A near 21 cm wavelength. In particular for Virgo A they observed a Gaussian absorption profile centred at a radial velocity of + 1,200 km s−1 with an optical depth of 59 ± 3 × 10−4 and a full width at half power of 920 km s−1. The purpose of this letter is to report that this particular measurement is negated by recent observations with the large radio telescope at Nancay. The upper limit for the amplitude of a Gaussian profile of the form reported by Koehler and Robinson is 2 × 10−3, which is one third of their positive result.