• 천문학회지
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• 제37권5호
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• pp.371-374
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• 2004

We review the observational evidence for the existence of a warm-hot intergalactic medium (WHIM). We expect that the morphology of this material is similar to that of cosmic rays and magnetic fields in large-scale structure, i.e., filaments connecting clusters of galaxies. Direct evidence for the WHIM, either in emission or absorption, is weak.

• 천문학회지
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• 제38권2호
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• pp.129-133
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• 2005

The temperature (T) and entropy (S) fields of baryonic gas, or intergalactic medium (IGM), in the ACDM cosmology are analyzed using simulation samples produced by a hybrid cosmological hydrodynamic/N-body code based on the weighted essentially non-oscillatory scheme. We demonstrate that, in the nonlinear regime, the dynamical similarity between the IGM and dark matter will be broken in the presence of strong shocks in the IGM. The heating and entropy production by the shocks breaks the IGM into multiple phases. The multiphase and non-Gaussianity of the IGM field would be helpful to account for the high-temperature and high-entropy gas observed in groups and clusters with low-temperature IGM observed by Ly$\alpha$ forest lines and the intermittency observed by the spikes of quasi-stellar object's absorption spectrum.

• 천문학회지
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• 제37권4호
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• pp.205-210
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• 2004

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.

• 천문학회지
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• 제37권5호
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• pp.343-347
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• 2004

The energy injection of galactic black holes (BH) into the intergalactic medium via extragalactic radio source jets and lobes is sufficient to magnetize the IGM in the filaments and walls of Large Scale Structure at < [B] > ${\~}0.l{\mu}G$ or more. It appears that this process of galaxy-IGM feedback is the primary source of IGM cosmic rays(CR) and magnetic field energy. Large scale gravitational infall energy serves to re-heat the intergalactic magnetoplasma in localities of space and time, maintaining or amplifying the IGM magnetic field, but this can be thought of as a secondary process. I briefly review observations that confirm IGM fields around this level, describe further Faraday rotation measurements in progress, and also the observational evidence that magnetic fields in galaxy systems around z=2 were approximately as strong then, ${\~}$10 Gyr ago, as now.

• 천문학논총
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• 제4권1호
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• pp.1-15
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• 1989

A jet plasmoid model for 3C.449 has been constructed by introducing a plasma.ejecting black hole orbiting around the center of its parent cD galaxy. We examined the characteristics of the jet trajectory by varying the values of (1) orbiting radius and velocity of the black hole, (2) plasma ejection velocity, (3) size, mass and space velocity of the parent galaxy, (4) size of the galactic core and (5) the density of the intergalactic medium. In our model calculation the effect of the gravity by the parent galaxy and the ram pressure by the intergalactic medium have been taken in account. It is found that our dynamical model accounts reasonably well for the observed structure of 3C449. Our proposed model suggests that the buoyancy force near the galactic center plays an important role in the formation of the curved structure of the radio jet.

• 천문학회보
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• 제41권2호
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• pp.35.2-35.2
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• 2016

Lyman alpha photons emitted from the early generation galaxies are scattered through the intergalactic medium, and can be observed as Lyman alpha emitting sources. We examine the Lyman alpha line transfer mechanism by tracing the random scattering histories of Lyman alpha photons in the intergalactic medium of the early universe. The density and ionization fields are based on the 3D map by N-body + radiation transfer simulations of the epoch of reionization. The calculation is compared with analytical models, too. The emergent line profile and the size of the Lyman alpha blob are strongly tied to the density and ionization environment, likely to give constraints when high-z Lyman alpha blobs are observed.

• 천문학회지
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• 제37권5호
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• pp.375-379
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• 2004

In this paper I give an overview of the detection of emission from the warm-hot intergalactic medium (WHIM) in the outer parts of clusters of galaxies. The evidence for the presence of soft excess X-ray emission in 7 out of 21 clusters is summarized, and it is demonstrated that several of these clusters show the signatures of thermal emission in the outer parts. A strong signature is the presence of redshifted O VII emission at 0.57 keV. In the central parts, several clusters show also a soft excess, but m this case the observations cannot well discriminate between a thermal or non-thermal origin of the soft X-ray excess.

• 천문학회지
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• 제37권5호
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• pp.447-454
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• 2004

During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.

• 천문학회지
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• 제37권5호
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• pp.579-581
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• 2004

Recently, claims have been made of the detection of 'warm-hot' gas in the intergalactic medium. Kaastra et al. (2003) claimed detection of ${\~} 10^6$ K material in the Coma Cluster but studies by Arnaud et al. (2001), and our analysis of the Chandra observations of Coma (Vikhlinin et al. 2001), find no evidence for a $10^6$ K gas in the cluster. Finoguenov et al. (2003) claimed the detection of $3 {\times} 10^6$ gas slightly off-center from the Coma Cluster. However, our analysis of ROSAT data from this region shows no excess in this region. We propose an alternative explanation which resolves all these conflicting reports. A number of studies (e.g. Robertson et al., 2001) have shown that the local interstellar medium undergoes charge exchange with the solar wind. The resulting recombination spectrum shows lines of O VII and O VIII (Wargelin et al. 2004). Robertson & Cravens (2003) have .shown that as much as $25\%$ of the Galactic polar flux is heliospheric recombination radiation and that this component is highly variable. Sporadic heliospheric emission could account for all the claims of detections of 'warm-hot' gas and explain the conflicts cited above.

• 천문학회지
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• 제47권5호
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• pp.187-193
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• 2014

Recent cosmological observations indicate that the reionized universe may have started at around z = 6, where a significant suppression around $Ly{\alpha}$ has been observed from the neutral intergalactic medium. The associated neutral hydrogen column density is expected to exceed $10^{21}cm^{-2}$, where it is very important to use the accurate scattering cross section known as the Kramers-Heisenberg formula that is obtained from the fully quantum mechanical time-dependent second order perturbation theory. We present the Kramers-Heisenberg formula and compare it with the formula introduced in a heuristic way by Peebles (1993) considering the hydrogen atom as a two-level atom, from which we find a deviation by a factor of two in the red wing region far from the line center. Adopting a representative set of cosmological parameters, we compute the Gunn-Peterson optical depths and absorption profiles. Our results are quantitatively compared with previous work by Madau & Rees (2000), who adopted the Peebles approximation in their radiative transfer problems. We find deviations up to 5 per cent in the Gunn-Peterson transmission coefficient for an accelerated expanding universe in the red off-resonance wing part with the rest wavelength ${\Delta}{\lambda}{\sim}10{\AA}$.