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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 57/122
561
- BLASI PASQUALE
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.483-491
- 2004
- 원문 바로보기
Clusters of galaxies are storage rooms of cosmic rays. They confine the hadronic component of cosmic rays over cosmological time scales due to diffusion, and the electron component due to energy losses. Hadronic cosmic rays can be accelerated during the process of structure formation, because of the supersonic motion of gas in the potential wells created by dark matter. At the shock waves that result from this motion, charged particles can be energized through the first order Fermi process. After discussing the most important evidences for non-thermal phenomena in large scale structures, we describe in some detail the main issues related to the acceleration of particles at these shock waves, emphasizing the possible role of the dynamical backreaction of the accelerated particles on the plasmas involved.
562
- LANGER MATHIEU
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.553-556
- 2004
- 원문 바로보기
We present a new model for the generation of magnetic fields on large scales occurring at the end of cosmological reionisation. The inhomogeneous radiation provided by luminous sources and the fluctuations in the matter density field are the major ingredients of the model. More specifically, differential radiation pressure acting on ions and electrons gives rise to electric currents which induce magnetic fields on large scales. We show that on protogalactic scales, this process is highly efficient, leading to magnetic field amplitudes of the order of <TEX>$10^{-1l}$</TEX> Gauss. While remaining of negligible dynamical impact, those amplitudes are million times higher than those obtained in usual astrophysical magnetogenesis models. Finally, we derive the relation between the power spectrum of the generated field and the one of the matter density fluctuations. We show in particular that magnetic fields are preferably created on large (galactic or cluster) scales. Small scale magnetic fields are strongly disfavoured, which further makes the process we propose an ideal candidate to explain the origin of magnetic fields in large scale structures.
563
- ASAI NAOKI
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.575-578
- 2004
- 원문 바로보기
High resolution observations of cluster of galaxies by Chandra have revealed the existence of an X-ray emitting comet-like galaxy C153 in the core of cluster of galaxies A2125. The galaxy C153 moving fast in the cluster core has a distinct X-ray tail on one side, obviously due to ram pressure stripping, since the galaxy C153 crossed the central region of A2125. The X-ray emitting plasma in the tail is substantially cooler than the ambient plasma. We present results of two-dimensional magnetohydrodynamic simulations of the time evolution of a sub clump like C153 moving in magnetized intergalactic matter. Anisotropic heat conduction is included. We found that the magnetic fields are essential for the existence of the cool X-ray tail, because in non-magnetized plasma the cooler sub clump tail is heated up by isotropic heat conduction from the hot ambient plasma and does not form such a comet-like tail.
564
- CASSANO R.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.583-587
- 2004
- 원문 바로보기
With the aim to investigate the statistical properties and the connection between thermal and non-thermal properties of the ICM in galaxy clusters, we have developed a statistical magneto-turbulent model which describes, at the same time, the evolution of the thermal and non-thermal emission from galaxy clusters. In particular, starting from the cosmological evolution of clusters, we follow cluster. mergers, calculate the spectrum of the magnetosonic waves generated in the ICM during these mergers, the evolution of relativistic electrons and the resulting synchrotron and Inverse Compton spectra. We show that the broad band (radio and hard x-ray) non-thermal spectral properties of galaxy clusters can be well accounted for by our model for viable values of the parameters (here we adopt a EdS cosmology).
565
- KRISHNA GOPAL
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.517-525
- 2004
- 원문 바로보기
We present an update on our proposal that during the 'quasar era' (1.5 <TEX>$\le$</TEX> z <TEX>$\le$</TEX> 3), powerful radio galaxies could have played a major role in the enhanced global star-formation, and in the widespread magnetization and metal pollution of the universe. A key ingredient of this proposal is our estimate that the true cosmological evolution of the radio galaxy population is likely to be even steeper than what has been inferred from flux-limited samples of radio sources with redshift data, when an allowance is made for the inverse Compton losses on the cosmic microwave background which were much greater at higher redshifts. We thus estimate that a large fraction of the clumps of proto-galactic material within the cosmic web of filaments was probably impacted by the expanding lobes of radio galaxies during the quasar era. Some recently published observational evidence and simulations which provide support for this picture are pointed out. We also show that the inverse Compton x-ray emission from the population of radio galaxies during the quasar era, which we inferred to be largely missing from the derived radio luminosity function, is still only a small fraction of the observed soft x-ray background (XRB) and hence the limit imposed on this scenario by the XRB is not violated.
566
- JOKIPII J. R.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.399-404
- 2004
- 원문 바로보기
Cosmic rays are ubiquitous in space, and are apparently present wherever the matter density is small enough that they are not removed by collisions with ambient particles. The essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. In comparison to shock acceleration, statistical acceleration, invoked in many situations, has significant disadvantages. The basic physics of acceleration and transport are discussed, and examples shown where it apparently works very well. However, there are now well-established situations where diffusive shock acceleration cannot be the accelerator. This problem will be discussed and possible acceleration mechanism evaluated. Statistical acceleration in these places is possible. In addition, a new mechanism, called diffusive compression acceleration, will be discussed and shown to be an attractive candidate. It has similarities with both statistical acceleration and shock acceleration.
567
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.137-141
- 2004
- 원문 바로보기
We have estimated the fractal dimension of the molecular clouds in the Antigalactic Center based on the <TEX>$^{12}CO$</TEX> (J = 1- 0) and <TEX>$^{13}CO$</TEX> (J = 1- 0) database obtained using the 14m telescope at Taeduk Radio Astronomy Observatory. Using a developed code within IRAF, we were able to identify slice-clouds, and determined the dispersions of two spatial coordinates as well as perimeters and areas. The fractal dimension of the target region was estimated to be D = 1.34 for low resolution <TEX>$^{12}CO$</TEX> (J = 1 - 0) database, and D = 1.4 for higher resolution <TEX>$^{12}CO$</TEX> (J = 1 - 0) and <TEX>$^{13}CO$</TEX> (J = 1 - 0) database, where <TEX>$P {\propto} A^{D/2}$</TEX>. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Our database with higher resolution of 1 arcminute, which is corresponding to 0.2 pc at a distance of 1.1 kpc, gives us the same estimate of fractal dimension to that of local dark clouds. Fractal dimension is apparently invariant when varying the threshold temperatures applied to cloud identification. According to the dispersion pattern of longitudes and latitudes of identified slice-clouds, there is no preference of elongation direction.
568
- GARCIA-SEGURA G.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.217-222
- 2004
- 원문 바로보기
High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous ob-served growth-rate discrepancy for supernova-driven super bubbles and stellar wind bubbles. Pressures of P / k <TEX>${\~} 10^5\;cm^{-3}$</TEX> K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that super bubbles ultimately might serve as ISM barometers.
569
- ENBLIN TORSTEN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.439-446
- 2004
- 원문 바로보기
A critical discussion of our knowledge about extragalactic cosmic rays and magnetic fields is at-tempted. What do we know for sure? What are our prejudices? How do we confront our models with the observations? How can we assess the uncertainties in our modeling and in our observations? Unfortunately, perfect answers to these questions can not be given. Instead, I describe efforts I am involved in to gain reliable information about relativistic particles and magnetic fields in extragalactic space.
570
- OLINTO ANGELA V.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.413-420
- 2004
- 원문 바로보기
The current state and future prospects of ultra high energy cosmic ray physics are reviewed. These cosmic rays with energies well above <TEX>$10^{18}$</TEX> eV are messengers of an unknown extremely high-energy universe.