• 천문학회보
• /
• 제46권1호
• /
• pp.29.3-29.3
• /
• 2021

Globular clusters (GCs) form at the very early stage of galaxy formation, and thus can be used as an important clue indicating the environment of the galaxy formation era. Although various GC formation scenarios have been suggested, they have not been examined in the cosmological context. Here we introduce the 'particle tagging method' in order to investigate the formation scenarios of GCs in a galaxy cluster. This method is able to trace the evolution of GCs that form in the dark matter halos which undergo the hierarchical merging events in galaxy cluster environments with an effective computational time. For this we use dark matter merger trees from the cosmological N-body simulation. Finally, we would like to find out the best GC formation scenario which can explain the observational properties of GCs in galaxy clusters.

• 천문학회지
• /
• 제38권2호
• /
• pp.161-164
• /
• 2005

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 ${\~}$ -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.

• 천문학회보
• /
• 제22권
• /
• pp.35.1-35.1
• /
• 1997

• 천문학회보
• /
• 제16권
• /
• pp.16.1-16.1
• /
• 1991

• Journal of Astronomy and Space Sciences
• /
• 제29권2호
• /
• pp.175-180
• /
• 2012

White dwarf stars have played important roles in rather diverse areas of astrophysics. This paper outlines how these stellar remnants, especially those in widely separated "fragile" binaries, have provided unique leverage on difficult astrophysical problems such as the ages of stars, the structure and evolution of the Galaxy, the nature of dark matter and even the discovery of dark energy.

• 천문학회보
• /
• 제38권1호
• /
• pp.32.2-32.2
• /
• 2013

We examine large-scale environmental effects on the formation and the mass growth of dark matter halos. To facilitate this, we constructed dark matter halo merger trees from a cosmological N-body simulation, which enabled us to trace the merger information and the assembly history of individual halos. In fact, since the massive halos are more likely to be distributed in denser regions than in less dense regions (Mo & White, 1996), the large-scale environment dependence of the properties of halos can be partly originated from the halo mass effect. In order to avoid such contamination, caused by the mass dependence of halo properties, we carefully measured the local overdensity as the indicator of large-scale environment, which was calculated to be as independent of halo mass as possible. Small halos (${\sim}10^{11-12}M_{\odot}$), which usually host isolated single galaxies, show a notable difference on the formation time of galaxies depending on their large-scale environments, which reconfirms halo assembly bias (Gao & White, 2007). Furthermore, we investigate how this environmental effect on small halos is correlated with the mass assembly history of galaxies by using our semi-analytic model. We found that assembly bias in small halos does not have significant effects on the formation time or on the star formation history of galaxies residing in those halos except for the individual stellar mass of galaxies at z = 0. On average, isolated galaxies in high-density regions tend to be slightly more massive than those in low-density regions. Although the observational data from the current galaxy surveys is not yet sufficient for testing this prediction, future galaxy surveys will be able to explore these small galaxies more thoroughly.

• 천문학논총
• /
• 제30권2호
• /
• pp.331-333
• /
• 2015

Gravitational interactions - mergers and fly-by encounters - between galaxies play a key role as the drivers of their evolution. Here we perform a cosmological N-body simulation using the tree-particle-mesh code GOTPM, and attempt to separate out the effects of mergers and fly-bys between dark matter halos. Once close pair halos are identified by the halo finding algorithm PSB, they are classified into mergers ($E_{12}$ < 0) and fly-by encounters ($E_{12}$ > 0) based on the total energy ($E_{12}$) between two halos. The fly-by and merger fractions as functions of redshift, halo masses, and ambient environments are calculated and the result shows the following.(1) Among Milky-way sized halos ($0.33-2.0{\times}10^{12}h^{-1}M{\odot}$), $5.37{\pm}0.03%$ have experienced major fly-bys and $7.98{\pm}0.04%$ have undergone major mergers since z ~ 1; (2) Among dwarf halos ($0.1-0.33{\times}10^{12}h^{-1}M{\odot}$), $6.42{\pm}0.02%$ went through major fly-bys and $9.51{\pm}0.03%$ experienced major mergers since z ~ 1; (3) Milky-way sized halos in the cluster environment experienced fly-bys (mergers) 4-11(1.5-1.7) times more frequently than those in the field since z ~ 1; and (4) Approaching z = 0, the fly-by fraction decreases sharply with the merger fraction remaining constant, implying that the empirical pair/merger fractions (that decrease from z ~ 1) are in fact driven by the fly-bys, not by the mergers themselves.

• 천문학회보
• /
• 제40권1호
• /
• pp.57.4-57.4
• /
• 2015

Light bending by gravity was the key prediction of general relativity. Solar eclipse expedition of 1919 provided the observational support for the theory of general relativity. Diverse gravitational lensing, i.e., light bending, phenomena have been speculated and predicted by general relativity and ultimately discovered many years later. Gravitationally lensed quasars, luminous arcs, weak lensing, and microlensing have provided invaluable information about the distribution of matter, especially of dark matter, and the cosmology. Gravitational lensing is one of the most spectacular manifestation of general relativity and will remain as an extremely useful astrophysical tools in the future.

• 천문학회보
• /
• 제44권1호
• /
• pp.57.1-57.1
• /
• 2019

In support of current and upcoming large-volume cosmological surveys such as the SDSS-IV eBOSS, LSST, and DESI, we present an extensive suite of high-resolution cosmological hydrodynamical simulations spanning a large range of cosmological and astrophysical parameters. We follow the evolution of gas, dark matter, neutrinos, and dark radiation, and consider several combinations of box sizes and number of particles - enhancing the resolution up to $3{\times}33283=110$ billion particles in a (100 h-1 Mpc)3 box size. We also provide 100,000 skewers for a variety of redshift slices and combination of cosmological and astrophysical parameters, useful for interpreting upcoming high-quality $Lyman-{\alpha}$ forest data. These novel simulations represent an improvement over our previous runs, and can be useful for a broader variety of cosmological and astrophysical applications, ranging from the three-dimensional modeling of the $Lyman-{\alpha}$ forest to cross-correlations between different probes, for studying the expansion history of the Universe including massive neutrinos, and for particle-physics related topics.

• 천문학회보
• /
• 제44권1호
• /
• pp.56.1-56.1
• /
• 2019

The concordance LCDM model has been very successful at reproducing a wide range of observations. However, the nature of its main components, such as dark energy, dark matter, and inflation, are still unkown. Therefore, it is of prime importance to question the underlying hypotheses of the model and tests there prediction. While most constraints have been obtained assuming a LCDM universe, model-independent approaches, which do not make assumptions regarding the model, are a powerful approach. To falsify the LCDM model, I applied model-indepedent methods to the latests available data to test different aspects of the concordance model, such as the FLRW metric, the curvature, dark energy as the cosmological constant, and gravity as general relativity. The Universe is consistent with flat-LCDM with GR. However, at z>1, tensions start to appear, and more data are required.