간행물
천문학회지 KCI 등재 SCOPUS Journal of The Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 반년간
- ISSN 1225-4614 (Print)2288-890X (Online)
- 수록기간 1968 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제38권 제2호 (2005년 6월) 68건
21.
2005.06
구독 인증기관 무료, 개인회원 유료
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 Lyα forest lines and the intermittency observed by the spikes of quasi-stellar object's absorption spectrum.
3,000원
22.
2005.06
구독 인증기관 무료, 개인회원 유료
This paper summarizes the recent progress made by our group at Seoul National University on studies of the evolution and formation of distant galaxies. Various research projects are currently underway, which include: (i) the number density of distant early-type galaxies (z < 1); (ii) the optical-NIR color gradient of nearby early-type galaxies; (iii) J - K-selected Extremely Red Objects (EROs) in field (CDF-S) and the cluster environment; and (iv) the Lyman-break galaxies in the Spitzer First Look Survey (FLS) field. These works will constrain the mass evolution and the star formation history of galaxies in different environments, and the results will serve as useful contraints on galaxy formation models.
4,000원
23.
2005.06
구독 인증기관 무료, 개인회원 유료
Based on optical galaxy data, we executed a systematic search for galaxy clusters around the 15 steady unidentified EGRET GeV gamma-ray sources in high Galactic-latitude sky (|b| > 30). We found a strong correlation with 3.7σ level between close cluster pairs (merging cluster candidates) and the unidentified EGRET sources, though, in contrast, no correlation with single clusters. This result implies that merging clusters of galaxies are a possible candidate for the origin of high galactic-latitude, steady unidentified EGRET gamma-ray sources.
3,000원
24.
2005.06
구독 인증기관 무료, 개인회원 유료
We present a photometric study of galaxies in the central regions of six nearby galaxy clusters at redshift z=0.0231~0.0951. We have derived BVI photometry of the galaxies from the CCD images obtained at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea, and JHKs photometry of the bright galaxies from the 2MASS extended source catalog. Comparing the galaxy photometry results with the simple stellar population model of Bruzual & Charlot (2003) in the optical & NIR color-color diagrams, we have estimated the ages and metallicities of early type galaxies. We have found that the observed galaxies had recent star-formation mostly 5 ~ 7 Gyrs ago but the spread in age estimation is rather large. The average metallicities are [Fe/H]=0.l~0.5 dex. These results support the hypothesis that large early type galaxies in clusters are formed via hierarchical merging of smaller galaxies.
3,000원
25.
2005.06
구독 인증기관 무료, 개인회원 유료
We have studied the environmental effect on optical-NIR color gradients of 273 nearby elliptical galaxies. Color gradient is a good tool to study the evolutionary history of elliptical galaxies, since the steepness of the color gradient reflects merging history of early types. When an elliptical galaxy goes through many merging events, the color gradient can be get less steep or reversed due to mixing of stars. One simple way to measure color gradient is to compare half-light radii in different bands. We have compared the optical and near infrared half-light radii of 273 early-type galaxies from Pahre (1999). Not surprisingly, we find that re(V)s (half-light radii measured in V-band) are in general larger than re(K)s (half-light radii measured in K-band). However, when divided into different environments, we find that elliptical galaxies in the denser environment have gentler color gradients than those in the less dense environment. Our finding suggests that elliptical galaxies in the dense environment have undergone many merging events and the mixing of stars through the merging have created the gentle color gradients.
3,000원
26.
2005.06
구독 인증기관 무료, 개인회원 유료
EUCHIRO KOKUBO, MITSURU HAYASHI, TSUNEHIKO KATO, TAKAAKI TAKEDA, NORIO KAIFU, SHOKEN MIYAMA, HITOSHI MIURA, TOSHIYUKI TAKAHEI
We have developed the four-dimensional digital universe theater at which we can visualize the observational data and theoretical models of astronomical objects stereoscopically. The astronomical objects cover all scales of the universe from the solar system to the large-scale structure of the universe. We have also produced the three-dimensional movies of various astronomical processes based on the results of computer simulations. We plan to distribute all the products of this project through the internet.
3,000원
27.
2005.06
구독 인증기관 무료, 개인회원 유료
To constrain the values of the model parameters for the cosmological models involving the time-decaying Λ term, we have computed sets of theoretical predictions for the N-m relation of galaxies as well as the CMB angular power spectrum: three types of variation, viz., Λ ∝ T-1, a-m, and Hn are thereby assumed following Overduin & Cooperstock (1998), although we concentrate here on the discussion of the results obtained from the first type. Our results for the N-m relation indicate that the observed excess of the galaxy counts N in the faint region beyond the blue apparent magnitude 24 can be reasonably well accounted for with the value of Ɩ in the range between 0.2 and 1. Furthermore, a comparison of our computational results of the CMB spectra with the observational data shows that the models with a mild degree of the Λ term decay, viz., with the value of Ɩ ≾ 0.4, are favorable. In this case, the age of our universe turns out to be larger than or equal to 14 Gyr, the lower limit inferred from some Uranium datings.
3,000원
28.
2005.06
구독 인증기관 무료, 개인회원 유료
We present a theoretical formalism by which the global and the local mass functions of dark matter substructures (dark subhalos) can be analytically estimated. The global subhalo mass function is defined to give the total number density of dark subhalos in the universe as a function of mass, while the local subhalo mass function counts only those sub halos included in one individual host halo. We develop our formalism by modifying the Press-Schechter theory to incorporate the followings: (i) the internal structure of dark halos; (ii) the correlations between the halos and the subhalos; (iii) the subhalo mass-loss effect driven by the tidal forces. We find that the resulting (cumulative) subhalo mass function is close to a power law with the slope of ${\~}$ 수식 이미지 -1, that the subhalos contribute approximately 10% of the total mass, and that the tidal stripping effect changes the subhalo mass function self-similarly, all consistent with recent numerical detections.
3,000원
29.
2005.06
구독 인증기관 무료, 개인회원 유료
We overview the GRAPE (GRAvity piPE) project. The goal of the GRAPE project is to accelerate the astrophysical N-body simulations. Since almost all computing time is spent for the evaluation of the gravitational force between particles, we can greatly accelerate many N-body simulations by developing a specialized hardware for the force calculation. In 1989, the first such hardware, GRAPE-1, was completed, with the peak speed of 120 Mflops. In 2003, GRAPE-6 was completed, with the peak speed of 64 Tflops, which is nearly 106 times faster than GRAPE-l and was the fastest computer at that time. In this paper, we review the basic concept of the GRAPE hardwares, the history of the GRAPE project, and two ongoing projects, GRAPE-DR and Project Milkyway.
3,000원
30.
2005.06
구독 인증기관 무료, 개인회원 유료
SATOKI MATSUSHITA, RUI-QING MAO, SEBASTIEN MULLER, CHUEN- YI CHOU, SATOKO SAWADA-SATOH, DINH-VAN TRUNG, JEREMY LIM, PEI-YING HSIEH, ALISON B. PECK
We present CO(3-2), CO(2-1), and 230 GHz (1.3 mm) continuum images of nearby galaxies taken with the Submillimeter Array (SMA). Our main topic is to study the relation between higher-J molecular gas (e.g., CO J=3-2, 2-1) and nuclear activities (e.g., active galactic nuclei [AGNs] and starbursts). The nearby Seyfert 2 galaxy M51 shows strong CO(3-2) emission from the circumnuclear molecular gas, with an intensity twice as strong as that of the CO(1-0) emission. Strong CO(3-2) emission enhancement suggests that the circum nuclear molecular gas in M51 is warm and dense, which may be related to the AGN activities. Molecular gas in the nearby moderate starburst galaxy NGC 6946 is distributed along the large-scale bar or spiral arms and along the minibar, and the multi-J CO line images show very similar distribution to each other. For this galaxy, there is no clear enhancement in higher-J lines as seen in M51, which may be because NGC 6946 does not have clear AGN activities. Based on the results of these two galaxies, the physical conditions of the circum nuclear molecular gas may be related to the AGN activities. We also observed the nearby edge-on starburst galaxy NGC 3628 and the starburst/Seyfert composite galaxy NGC 4945 with the CO(2-1) line and 230 GHz (1.3 mm) continuum emission. These information will give us some hints for understanding the relation between nuclear activities and circum nuclear molecular gas and dust.
3,000원
31.
2005.06
구독 인증기관·개인회원 무료
On behalf of the IRSF/SIRIUS group, I introduce some recent results from our deep near-infrared surveys (J, Hand Ks bands, limiting magnitude of Ks=17) toward star forming regions in the Milky Way Galaxy (MWG) and Large Magellanic Cloud (LMC) with the near-infrared camera SIRIUS. We discovered a rich population of low-mass young stellar objects associated with the W3 and NGC 7538 regions in the MWG based on the near-infrared colors arid magnitudes. The high sensitivity of our survey enables us to detect intermediate-mass pre-main sequence stars, i.e. HAEBE stars, even in the LMC. We detected many HAEBE candidate stars in the N159/N160 complex star forming region in the LMC with the IRSF 1.4-m telescope. Spatial distributions of the young stellar objects indicate the sequential cluster formation in each star forming region in the complex and large scale (a few X 100 pc) sequential cluster formation over the entire complex.
32.
2005.06
구독 인증기관 무료, 개인회원 유료
We show that next-generation galaxy surveys such as KAOS (the Kilo-Aperture Optical Spectro-graph)will constrain dark energy even if the baryon oscillations are missing from the monopole power spectrum and the bias is scale- and time-dependent KAOS will accurately measure the quadrupole power spectrum which gives the leading anisotropies in the power spectrum in redshift space due to peculiar velocities, the finger of God effect, as well as the Alcock-Paczynski effect. The combination of monopole and quadrupole power spectra powerfully breaks the degeneracy between the bias parameters and dark energy and, in the complete absence of baryon oscillations (Ωb = 0), leads to a roughly 500% improvement in constraints on dark energy compared with the monopole spectrum alone. As a result, for KAOS the worst case with no oscillations has dark energy errors only mildly degraded relative to the ideal case, providing insurance on the robustness of KAOS constraints on dark energy. We show that nonlinear effects are crucial in correctly evaluating the quadrupole and significantly improving the constraints on dark energy when we allow for multi-parameter scale-dependent bias.
3,000원
33.
2005.06
구독 인증기관 무료, 개인회원 유료
We conducted an extremely wide field survey of z ~ 6 Lyman break galaxies (LBGs) to precisely derive their bright end surface density overcoming the bias due to cosmic variance. We selected out LBG candidates in the Subaru/ XMM-Newton Deep Survey Field (SXDS) over the total of 1.0 deg2 sky area down to z'AB = 26.0 (≳ 3σ, 2"0 aperture) using i' - z' > 1.5 color cut. This sample alone is likely to be contaminated by M/L/T dwarfs, low-z elliptical galaxies, and z ~ 6 quasars. To eliminate these interlopers, we estimated their numbers using an exponential disk star count model, catalogs of old ellipticals in the SXDS and other field, and a z ~ 6 quasar luminosity function. The finally derived surface density of z ~ 6 LBGs was 165 mag-1 deg-2 down to z'AB = 26.0 and shows good agreement with previous results from the narrower field survey of HST GOODS.
3,000원
34.
2005.06
구독 인증기관 무료, 개인회원 유료
We present results of the VLBA observation toward the radio continuum and water maser emissions in a nearby LINER galaxy NGC 1052. The jet structure observed in 2000 is similar to that in 1998, and the two jet structures in 1998 and 2000 support the sub-luminal motion with apparent velocity of 0.26c. Distribution of water maser spots are located ~0.05 pc shifted to southwest from the component which is supported to be the nucleus, and no rapid positional change of the water maser gas with respect to the central engine is seen from 1995 to 2000. The maser gas is positionally coincident with a plasma torus, and the position of the maser gas relative to the nucleus is stable from 1995 to 2000. The maser gas in NGC 1052 could be explained to be associated with the nuclear circumnuclear torus or disk like the situation found in the nucleus of NGC 4258.
3,000원
35.
2005.06
구독 인증기관 무료, 개인회원 유료
YOSHIAKI TANIGUCHI, N. Z. SCOVILLE, D. B. SANDERS, B. MOBASHER, H. AUSSEL, P. CAPAK, M. AJIKI, T. MURAYAMA, S. MIYAZAK, Y. KOMIYAMA, T. NAGAO, S. SASAKI, R. SUMIYA, J. KODA, L. HEINLEIN, Y. HATAKEYAMA, H. KAROJI, COSMOS TEAM
The Cosmic Evolution Survey (COSMOS) is a Hubble Space Telescope (HST) treasury project. The COSMOS aims to perform a 2 square degree imaging survey of an equatorial field in I(F814W) band, using the Advanced Camera for Surveys (ACS). Such a wide field survey, combined with ground-based photometric and spectroscopic data, is essential to understand the interplay between large scale structure, evolution and formation of galaxies and dark matter. In 2004, we have obtained high-quality, broad band images of the COSMOS field (B, V, r', i', and z') using Suprime-Cam on the Subaru Telescope, and we have started our new optical multi-band program, COSMOS-21 in 2005. Here, we present a brief summary of the current status of the COSMOS project together with contributions from the Subaru Telescope. Our future Subaru program, COSMOS-21, is also discussed briefly.
3,000원
36.
2005.06
구독 인증기관 무료, 개인회원 유료
We used Subaru observations of A1689 (z = 0.183) to derive an accurate, model-independent mass profile for the entire cluster, r ≾ 2Mpc/h, by combining magnification bias and distortion measurements. The projected mass profile steepens quickly with increasing radius, falling away to zero at r ~1.0Mpc/h, well short of the anticipated virial radius. Our profile accurately matches onto the inner profile, r ≾ 200kpc/ h, derived from deep HST / ACS images. The combined ACS and Subaru information is well fitted by an NFW profile with virial mass, (1.93 ± 0.20) X 1015M⊙, and surprisingly high concentration, Cvir = 13.7+1.4-1.1, significantly larger than theoretically expected (Cvir ≃4), corresponding to a relatively steep overall profile. These results are based on a reliable sample of background galaxies selected to be redder than the cluster E/SO sequence. By including the faint blue galaxy population a much smaller distortion signal is found, demonstrating that blue cluster members significantly dilute the true signal for r ≾ 400kpc/ h. This contamination is likely to affect most weak lensing results to date.
4,000원
37.
2005.06
구독 인증기관 무료, 개인회원 유료
It is well known that a rotating bar potential can transport angular momentum to the disk and hence cause the evolution of the disk. Such a process is particularly important in disk galaxies since it can result in fuelling AGNs and starburst ring activities. In this paper, we will present the numerical simulations to show how this mechanism works. The problem, however, is quite complicated. We classify our simulations according to the type of Lindbald resonances and try to single out the individual roles they play in the disk evolution. Among many interesting results, we emphasize the identification of the origin of the starburst rings and the dense circumnuclear molecular disks to the instability of the disk. Unlike most of the other simulations, the self-gravitation of the disk is emphasized in this study.
4,000원
38.
2005.06
구독 인증기관 무료, 개인회원 유료
The large field multi-color CCD sky survey program based on the 60/90 Schmidt telescope of NAOC has been processed in cooperation among many observatories and universities of Asian countries. The observation and scientific results are reviewed.
3,000원
39.
2005.06
구독 인증기관 무료, 개인회원 유료
We study the influence of rotation on the dynamical evolution of collisional single-mass stellar clusters up to core-collapse by using N-body simulations. Rotating King models which are characterized by dimensionless central potential parameter Wo and the rotation parameter Wo are used as initial models. Our results show that inner shells slowly contract until core-collapse phase is reached, followed by a slow expansion. Angular momentum is transported outward, while the core is rotating even faster than before, as predicted by gravogyro catastrophe theory. We confirm that rotation plays an important role in accelerating the dynamical evolution of stellar cluster, in particular in accelerating the core collapse.
3,000원
40.
2005.06
구독 인증기관 무료, 개인회원 유료
We performed a spatially resolved spectroscopic study of the thermal composite supernova remnant 3C 391 by the Chandra observation. Broad- and narrow-band X-ray images show a southeast-northwest elongated morphology and unveil a highly clumpy structure of the remnant. The spectral analysis for. the small-scale features indicates normal metal abundance and uniform temperature for the interior gas. The properties of the hot gas are largely in agreement with the cloudlet evaporation model as a main mechanism for the 'thermal composite' X-ray appearance, though radiative rim and thermal conduction may also be effective. An unresolved X-ray source, with a power-law spectrum, is observed on the northwest border. The equivalent width images reveal a faint finger-like protrusion in Si and S lines out of the southwest radio border.
3,000원
