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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 58/122
571
- KRONBERG PHILIPP P.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.343-347
- 2004
- 원문 바로보기
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] > <TEX>${\~}0.l{\mu}G$</TEX> 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, <TEX>${\~}$</TEX>10 Gyr ago, as now.
572
- KUWABARA TAKUHITO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.601-603
- 2004
- 원문 바로보기
We present the results of the linear analysis for the Parker-Jeans instability in the magnetized gas disks including the effect of cosmic-ray diffusion along the magnetic field lines. We adopted an uni-formly rotating two temperature layered disk with a horizontal magnetic fields and solved the perturbed equations numerically. Fragmentation of gases takes place and filamentary structures are formed by the growth of the instability. Nagai et al. (1998) showed that the direction of filaments being formed by the Parker-Jeans instability depends on the strength of pressure outside the unperturbed gas disk. We found that at some range of external pressures the direction of filaments is also governed by the value of the diffusion coefficient of CR along the magnetic field lines k.
573
- FERETTI L.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.315-322
- 2004
- 원문 바로보기
Several arguments have been presented in the literature to support the connection between radio halos and cluster mergers. The spectral index distributions of the halos in A665 and A2163 provide a new strong confirmation of this connection, i.e. of the fact that the cluster merger plays an important role in the energy supply to the radio halos. Features of the spectral index (flattening and patches) are indication of a complex shape of the radiating electron spectrum, and are therefore in support of electron reacceleration models. Regions of flatter spectrum are found to be related to the recent merger. In the undisturbed cluster regions, instead, the spectrum steepens with the distance from the cluster center. The plot of the integrated spectral index of a sample of halos versus the cluster temperature indicates that clusters at higher temperature tend to host halos with flatter spectra. This correlation provides further evidence of the connection between radio emission and cluster mergers.
574
- MAZZOTTA PASQUALE
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.381-385
- 2004
- 원문 바로보기
Similarly to other cluster of galaxies previously classified as cooling flow systems, the Chandra observation of MKW 3s reveals that this object has a complex X-ray structure hosting both a X-ray cavity and a X-ray filament. Unlike the other clusters, however, the temperature map of the core of MKW 3s shows the presence of extended regions of gas heated above the radially averaged gas temperature at any radius. As the cluster does not show evidences for ongoing major mergers Mazzotta et al. suggest a connection between the heated gas and the activity of the central AGN. Nevertheless, due to the lack of high quality radio maps, this interpretation was controversial. In this paper we present the results of two new radio observations of MKW 3s at 1.28 GHz and 604 MHz obtained at the GMRT. Together with the Chandra observation and a separate VLA observation at 327 MHz from Young, we show unequivocal evidences for a close connection between the heated gas region and the AGN activity and we briefly summarize possible implications.
575
- RYU DONGSU
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.477-482
- 2004
- 원문 바로보기
Shock waves form in the intergalactic space as an ubiquitous consequence of cosmic structure formation. Using N-body/hydrodynamic simulation data of a ACDM universe, we examined the properties of cosmological shock waves including their morphological distribution. Adopting a diffusive shock acceleration model, we then calculated the amount of cosmic ray energy as well as that of gas thermal energy dissipated at the shocks. Finally, the dynamical consequence of those cosmic rays on cluster properties is discussed.
576
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.131-135
- 2004
- 원문 바로보기
The <TEX>$H_2S\;(2_{2,0} - 2_{1,1})$</TEX> line emission is observed to be strongly localized toward Sgr B2(M), and emissions from other positions in the more extended SgrB2 region are almost negligible. <TEX>$H_2S$</TEX> is thought to form effectively by the passage of the C-type shocks but to be quickly transformed to <TEX>$SO_2$</TEX> or other sulfur species (Pineau des Forets et al. 1993). Such a shock may have enhanced the <TEX>$H_2S$</TEX> abundance in Sgr B2(M), where massive star formation is taking place. But the negligible emission of <TEX>$H_2S$</TEX> from other observed positions may indicate that these positions have not been affected by shocks enough to produce <TEX>$H_2S$</TEX>, or if they have experienced shocks, <TEX>$H_2S$</TEX> may have transformed already to other sulfur-containing species. The <TEX>$SO_2\;22_{2,20} - 22_{1,21}$</TEX> line was also observed to be detectable only toward the (M) position. The line intensity ratios of these two molecules appear to be very similar at Sgr B2(M) and IRAS 16239-2422, where the latter is a region of low-mass star formation. This may suggest that the shock environment in these two star-forming regions is similar and that the shock chemistry also proceeds in a similar fashion in these two different regions, if we accept shock formation of these two species.
577
- KANG HYESUNG
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.405-412
- 2004
- 원문 바로보기
Cosmological shocks form as an inevitable consequence of gravitational collapse during the large scale structure formation and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration (DSA). We have calculated the evolution of CR modified shocks for a wide range of shock Mach numbers and shock speeds through numerical simulations of DSA in 1D quasi-parallel plane shocks. The simulations include thermal leakage injection of seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion is assumed. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies (p/mc <TEX>$\ge$</TEX> 1), and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that <TEX>$10^{-4} - 10^{-3}$</TEX> of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The CR acceleration efficiency increases with shock Mach number, but it asymptotes to <TEX>${\~}50\%$</TEX> in high Mach number shocks, regardless of the injection rate and upstream CR pressure. On the other hand, in moderate strength shocks (<TEX>$M_s {\le} 5$</TEX>), the pre-existing CRs increase the overall CR energy. We conclude that the CR acceleration at cosmological shocks is efficient enough to lead to significant nonlinear modifications to the shock structures.
578
- LEE CHANG WON
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.257-259
- 2004
- 원문 바로보기
We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines to study inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect to <TEX>$N_2H^+$</TEX> are found to correlate well with each other and to have similar number distributions, implying that, in many cores, systematic inward motions of gaseous material may occur over a range of density of at least a factor <TEX>${\~}$</TEX>4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidates suggest that the median effective line-of-sight speed of the inward-moving gas is <TEX>${\~}0.07 km\;s^{-l}$</TEX> for CS (3-2) and <TEX>${\~} 0.04 km\;s^{-l}$</TEX> for CS(2-1). Considering that the optical depth obtained from the fits is usually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, denser gas with greater inward motions than CS(2-1) implying that many of the infall candidates have faster infall toward the center. However, this conclusion may not be representative of all starless core infall candidates, due to the statistically small number analyzed here. Further line observations will be useful to test this conclusion.
579
- SANTILLAN ALFREDO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.233-235
- 2004
- 원문 바로보기
High-velocity clouds are flows of neutral hydrogen, located at high galactic latitudes, with large velocities (<TEX>$[VLSR]{\ge} 100 km/s$</TEX>) that do not match a simple model of circular rotation for our Galaxy. Numerical simulations have been performed for the last 20 years to study the details of their evolution, and their possible interaction with the Galactic disk. Here we present a brief review of the models that have been already published, and describe newly performed three-dimensional magnetohydrodynamic simulations.
580
- 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.