Intergalactic Matter Research Articles

Patchy structure and selective extinction

In 1934 Bok argued that the observed phenomenon of clustering of galaxies could not be caused by intergalactic dust matter distributed like the interstellar clouds of dust in the Milky Way. Bok considered background clusters between foreground clusters of galaxies, while Zwicky investigated distant concentrations of galaxies through foreground clusters. Regarding the most distant chains of galaxies observed in the blue band, we investigate the foreground obscuration caused by dust. We indicate the case that galaxies between long chains of galaxies may be considered as obscured by solid grains, familiar of early investigations in statistical astronomy; probably the extinction law is similar to interstellar extinction. We agree with Zwicky's view that intergalactic matter affects the clustering of galaxies: moreover, we extend his research programme to the space between clusters of galaxies. Contrary to half-century tradition, the large clouds of grains similar to the grains occurring in the atmosphere of some stars must be taken as a real factor in the coil of complicated problems connected with the clustering of galaxies.

Molecules in the early universe

view Abstract Citations (236) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecules in the early universe Lepp, S. ; Shull, J. M. Abstract Calculations are presented of the formation of astrophysically interesting molecules (H2, HD, LiH, and HeH+) by gas-phase reactions during the postrecombination epoch (redshifts z = 300-30). In standard Friedmann cosmological models, H2/H is approximately equal to 10 to the -6th, HD/H2 is approximately equal to 10 to the -4.5th, and LiH/H2 is approximately equal to 10 to the -6.5th. These molecules may dominate the cooling and trigger the collapse of primordial gas clouds. The dipole rotational transitions of HD and LiH are particularly important at high density and low temperature. Additional molecules form during spherical collapse of these clouds, and their rotational cooling keeps the gas temperature between 400 and 1500 K over 12 decades of density increase until the H2 lines becomes optically thick. The existence of molecular coolants at high redshift has significant implications for the first generation of stars and for thermal instabilities in intergalactic matter. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/162013 Bibcode: 1984ApJ...280..465L Keywords: Cosmochemistry; Cosmology; Gravitational Collapse; Interstellar Gas; Molecular Clouds; Universe; Astronomical Models; Chemical Evolution; Hydrogen Recombinations; Red Shift; Stellar Evolution; Astrophysics full text sources ADS |

On the role of instabilities in unsteady-beam models of extended radio sources

Rayleigh–Taylor, Kelvin–Helmholtz and drift-wave instabilities are studied in the context of the heads of unsteady-beam models of extended radio sources, and the physical consequences of this preliminary analysis are discussed. It is shown that the Rayleigh–Taylor instability sets in on small scales, although complete mixing of the head and ambient materials might not occur. Thus tails may be knotty or have a shell structure (depending upon the nature of the unsteadiness of the beam) whilst hotspots are unlikely to contain any entrained intergalactic material. It is argued that Kelvin–Helmholtz and drift-wave instabilities tend to be suppressed by field shear and density gradients in the interface between the shocked beam and shocked intergalactic flows.

Ultraviolet spectroscopy of interstellar and intergalactic matter

Ultraviolet radiation in absorption and emission provides diagnostics of interstellar and intergalactic matter. After reviewing some basic physical reasons for the importance of UV astronomy, the UV observations of both media, the future uses of high resolution spectrometers in the far UV, and the atomic data required for proper interpretation are discussed. Satellite UV observations have the potential of answering fundamental questions dealing with the nature of the gaseous matter in the outer regions of our galaxy, in neighboring galaxies, and in the intergalactic matter seen in quasar absorption spectra.

X-ray absorption effects due to intergalactic abundance of carbon

The absorption effects at the soft X-ray and hard ultraviolet wavelengths due to some model abundance of intergalactic carbon material have been investigated for different cosmologies. Even though the local density, 2 × 109 <ϱ 0 = 1.0 × 10−34 g cm−3 of the absorbing component of the intergalactic material in the form of carbon is not adequate for the thermalization of the discrete background radiation, the amount of absorption in the X-rays up to the Hubble radius is not negligible.

Gravitational instability in the early universe - The growth of cluster-sized density perturbations

view Abstract Citations (17) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gravitational instability in the early universe: the growth of cluster-sized density perturbations. Perrenod, S. C. Abstract The growth of density perturbations in the early universe is computed for the case of spherical perturbations with a surrounding 'hole'. The analytical results are applied to the problem of infalling intergalactic material for the case of the Coma cluster, and it is found that the constraint given by Gunn and Gott (1972) on the amount of infallen material is relaxed only slightly. The location of the 'turnaround' radius near clusters is also computed. Although the turnaround radius Rt is insensitive to q0, the fraction of mass within Rt which is not yet virialized varies significantly with q0. It is suggested that the high X-ray luminosity of superclusters is due to the enhanced growth by gravitational instability of individual clusters in a supercluster environment. These individual X-ray clusters are likely to be of sufficient luminosity to explain the supercluster X-ray emission. Publication: The Astrophysical Journal Pub Date: September 1978 DOI: 10.1086/156376 Bibcode: 1978ApJ...224..285P Keywords: Galactic Clusters; Galactic Evolution; Gravitational Collapse; Space Density; Universe; X Ray Sources; Astronomical Models; Cosmology; Density Distribution; Gravitational Fields; Hubble Diagram; Astrophysics; Superclusters:X Rays; Universe: Density Perturbations full text sources ADS |

Observations of the outflow of gas from the nucleus of NGC 253 and its implications for the stellar population of the nucleus

The ionized gas in the central region of the nearby spiral galaxy NGC 253 was observed spectrographically. Between 15 and 25 arc seconds SE of the nucleus, the emission lines are resolved into two components; this result rules out a two-dimensional distribution of the gas and establishes that there is gas above the disk. From an argument based on the observed variation of the velocity with distance from center and on the similarity of the velocities of the ionized gas and of the H I observed in 21 cm absorption in front of the central radio source, it is concluded that the ionized gas observed along the minor axis at velocities lower than the systemic velocity is flowing out of the nucleus, rather than into the nucleus. Gas at velocity higher than the systemic velocity is also observed along the minor axis at 15 to 30 arcsec SE of the nucleus; there are several plausible interpretations for it. If this gas is outside the disk, it is either partaking in the same outflow as the gas at low velocities or it is falling on the disk; in this case, however, it cannot be pristine intergalactic material since it emits nitrogenmore » lines, but it could be gas ejected from the nucleus and falling back on the plane. If the gas at high velocity is in the disk, then it is in an expanding arm located 2.2 kpc from the center and having a radial motion of 80 km s/sup -1/. This appears the most likely interpretation. The rate of mass loss from the nucleus is estimated to be greater than or equal to 10/sup -2/ M sub solar per year. The outflow of ionized gas is a transient phenomenon; otherwise it would deeplete the central region 150 pc in radius in 10/sup 9/ years. It is shown that 1000 O6 stars can produce the ionizing flux necessary to keep the gas ionized and the energy to accelerate it. An exotic explosive phenomenon does not appear necessary to account for the observations. 8 figures, 2 tables.« less

Limit on the frequency of intergalactic supernovae

WE shall turn the simple observation that “there are no intergalactic supernovae” into a quantitative statement for the Coma cluster of galaxies. In this cluster, where at least 30% of the total luminosity lies outside the regions normally associated with individual galaxies1–3, the absence of intergalactic supernovae can be used to derive restrictions on the nature of the luminous intergalactic material, be it a diffuse collection of stars, a background of low surface brightness dwarf galaxies, or some other form of luminous matter.

Collisions of galaxies in dense clusters. II - Dynamical evolution of cluster galaxies

The application of the results of the numerical and analytic investigation of single collisions described in a previous paper to galaxies residing in dense clusters has yielded a number of interesting results. If the galaxies in the core start out with extended halos 500 kpc in extent that encompass all the mass in the cluster, then about 90 percent of the mass and 25 percent of the luminosity are liberated in a Hubble time. The properties of this intergalactic material suggest that it is properly identified with the halo of the cD galaxy. The interval velocity dispersions of the stripped galaxies should be lower than the initial dispersion. The details of the above results depend on the validity of the King model approximation after substantial mass loss has occurred. Finally two-body relaxation: in this case galaxy-galaxy encounters: should occur on the same time scale. The results obtained are suggestive of identifying either the Bautz-Morgan contrast classification or Oemler's morphological classification as density sequences, or equivalently sequences of increasing importance of dynamical or collisional effects on the cluster galaxies. (AIP)

Theoretical intensities of low frequency recombination lines

The possibility of observable recombination lines below 200 MHz is shown to be greatest for the case of negative absorption in low-density gas in front of strong radio sources. The amplification of background radiation can conceivably exceed 100 per cent, especially when the electron temperature is low; on the other hand if the temperature is sufficiently high, dielectronic recombination may give rise to detectable recombination lines from elements other than hydrogen. The optimum frequencies are in the range 50–200 MHz for the interstellar medium, and 1–100 MHz for such intergalactic matter as may exist. The effects of external radiation fields, thermal and nonthermal, are explored quantitatively and the relevantb n -factors computed for a 1000-level atom; it is found that even the general galactic radiation field will significantly alter the atomic level populations. Observations of these masing low-frequency recombination lines would be useful in sorting out the hot and cold components of the interstellar medium, and in investigating their properties.

Apparent magnitudes, redshifts, and inhomogeneities in the universe

view Abstract Citations (16) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Apparent magnitudes, redshifts, and inhomogeneities in the universe. Roeder, R. C. Abstract The apparent magnitude-redshift data of Sandage and Hardy have been analyzed using inhomogeneous zero-shear models of the universe and treating both the acceleration factor and the amount of intergalactic material as parameters to be determined by the data. The value found for the acceleration factor depends on the homogeneity factor and on the evolutionary correction assumed for the absolute magnitudes of galaxies, but may possibly be greater than 0.5, in which case the universe is 'closed.' Publication: The Astrophysical Journal Pub Date: March 1975 DOI: 10.1086/153453 Bibcode: 1975ApJ...196..671R Keywords: Astronomical Models; Galactic Evolution; Intergalactic Media; Red Shift; Universe; Acceleration (Physics); Inhomogeneity; Radial Velocity; Astrophysics full text sources ADS |

Intergalactic Matter and Radiation and its Bearing on Galaxy Formation and Evolution

An up-dated review is given of the evidence for the presence of intergalactic matter and radiation in the Universe. It is concluded that the only important constituents which may make a sizable contribution to the total mass-energy are intergalactic gas and condensed objects with a very high mass-to-light ratio. If the QSOs are not at cosmological distances, cold atomic hydrogen may still be the most important constituent and may contribute much more mass than do the galaxies. The X-ray observations still do not unambiguously show that very hot gas is present, though it is very likely on general grounds that some hot gas is present in clusters of galaxies.The question of whether or not large amounts of matter, enough to close the Universe, are present, remains unsettled. From the theoretical standpoint the answer depends almost completely on the approach taken to the problem of galaxy formation and to the cosmological model which is favoured.

High Velocity Neutral Hydrogen Clouds

A review is given of the observations of neutral hydrogen high velocity clouds (|ν| &gt; 80 km s−1) in and near the Galaxy. The positive and negative clouds are seen to have different distributions in the sky, following roughly the velocity pattern of galactic rotation. A characteristic of the majority of the clouds is their distribution in elongated bands or strings. The various theories of origin of HVCs are discussed; the possible role of the tidal interactions between the Magellanic Clouds and the Galaxy is emphasized. Tests are suggested to distinguish between the Oort theory of the infall of intergalactic material and theories which envisage the HVCs as originating in the outermost spiral structure.

Primordial Random Motions and Angular Momenta of Galaxies and Galaxy Clusters

We study the decay of primordial random motions of galaxies and galaxy clusters in an expanding universe by solving a kinetic equation for the relaxation of differential energy spectra N(E, t). Systematic dissipative energy losses are included, involving gravitational drag by, and accretion of, intergalactic matter, as well as the effect of collisions with other systems. Formal and numerical solutions are described for two distinct modes of galaxy formation in a turbulent medium, corresponding to formation at a distinct epoch and to continuous formation of galaxies. We show that any primordial random motions of galaxies at the present epoch can amount to at most a few km , and that collisions at early epochs can lead to the acquisition of significant amounts of primordial angular momentum. Subject headings: cosmology - galaxies - galaxies, clusters of - intergalactic medium

Star Formation and Evolution in Spiral Galaxies

Evolutionary models for regions of M31 and M33 and the solar neighborhood are based on a stellar birthrate suggested by the dynamics of spiral structure: we assume that stars are formed very efficiently until the gas content reaches equilibrium at its present value, which takes about 10 years; thereafter, the birthrate just equals the rate at which gas enters the system from stellar mass-loss or infall of intergalactic matter. Each model represents an average around a cylindrical- shell-shaped region, which is homogeneous and closed except for possible infall. The disk and spiral-arm populations only are considered. Each star is followed in the H-R diagram from the main sequence to death as an invisible remnant. Integrated magnitudes, colors, mass-to-light ratio (M/L), gas content, helium and metal abundance (Z), are computed in steps of 10 years. For regions of M31 and M33 we use only the Salpeter initial mass function (IMF). With this restriction, successful models can be obtained provided the infall rate and lower mass limit are suitably chosen. The gradient of lower limit required to give the observed gradient of MIL results in a decrease outwards of Z, in qualitative agreement with observation. The solar-neighborhood IMF is adjusted to give rise to the observed present-day luminosity function at age 11 x 10 years. The rapid initial birthrate results in such depletion of deuterium that, if there is no infalling intergalactic gas, the solar abundance cannot be explained; also, the solar Z is far too great unless at least half of the local hydrogen is hidden in molecular form. But if infall occurs at 2 percent of the local mass per 10 years, we can obtain a model which solves these problems and is consistent with the local M/L, distribution of Z among Ci dwarfs, abundances of long-lived r-process elements, supernova rate, and birthrate of white dwarfs. Subject headings: abundances, stellar - galaxies - galaxies, motions in - star formation - stellar statistics

Enrichment of Intergalactic Matter

The primordial gas out of which the Galaxy condensed may have been significantly enriched in heavy elements. A specific mechanism of enrichment is described, in which quasi-stellar sources eject enriched matter into the intergalactic medium. This matter is recycled through successive generations of these sources, and is progressively enriched. The enriched intergalactic matter is accreted by the protogalaxy and we find, for rates of mass ejection by quasi-stellar sources equal to about one solar mass per year in heavy elements, that this mechanism can account for the heavy-element abundances in the oldest Population II stars. Expressions are given for the degree of enrichment of the intergalactic gas as a function of redshift, and we show that our hypothesis implies that the present density of intergalactic gas must be at least a factor 3 larger than the mean density in galaxies at the present epoch.

Effect of Infalling Matter on the Heavy Element Content of a Galaxy

I HAVE considered1 some of the possible implications of infall of intergalactic matter in galaxies, a process which was proposed by Oort2 to explain the 21 cm observations of high velocity hydrogen “clouds” in our Galaxy. It was pointed out that infall of matter may have a number of important consequences for the structure and evolution of galaxies. In this communication I shall consider in more detail one of these possible consequences, namely the effect of continuing infall of matter on the composition of the interstellar medium and the Population I component of a galaxy. I shall show that in the presence of infalling matter the heavy element content of the interstellar material will tend to approach a constant value which is independent of both the infall rate and the early history of the galaxy and depends only on stellar evolution processes.

Infall of Matter in Galaxies

Arguments based on the existence of intergalactic matter are advanced to show that this matter may interact with and be accreted by galaxies to produce observable consequences. The diversity of the phenomena that results from such processes offers a possible understanding of some of the properties of extragalactic systems.

Intergalactic Matter and Radiation

This paper presents a critical discussion of our present knowledge of intergalactic matter and radiation as it relates to cosmology. While there have been some observational successes and much theoretical speculation, studies of intergalactic matter and radiation have still not allowed us to draw certain conclusions about the origin and evolution of the universe.

The Cosmic Background Radiation: Some Recent Developments

Diffuse background radiation has been detected over 16 decades of frequency - from a few MHz up to ~3 × 1016 MHz (100 MeV) - and there are upper limits over an even wider range. Generally an important contribution comes from the galactic disc, but in some wavebands it has proved possible to isolate a truly cosmic isotropic component originating beyond our own Galaxy. A simple Olbers-type argument shows that the bulk of any extragalactic radiation field originates at cosmological distances. This is true whether the radiation is emitted by discrete sources, or comes from extragalactic (or pregalactic) space. Thus studies of the isotropie background radiation, or even upper limits to its intensity, yield data that are vital for cosmology, as well as telling us something about the properties of diffuse intergalactic matter, and about intrinsically faint extragalactic objects which cannot be observed individually.In this talk I shall not attempt a systematic review of this extensive subject, but will merely discuss a few recent developments. I shall give special attention to the microwave and X-ray regions of the spectrum, as these are the two bands in which the cosmic background is so strong that it swamps the emission from the Galaxy.