• 천문학회보
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• 제36권2호
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• pp.76.2-76.2
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• 2011

It is widely accepted that the SED of a galaxy relates to its morphology. In addition, the SED of the galaxy is closely connected to its star formation history, and its morphological properties are affected by the merger history, interactions with its environment, and the gravitational instability of its dynamical system. Thus, it is likely that star formation history correlates to the elements that determine morphological properties. Among the elements, this study investigates how much the merger histories of galaxies influence their star formation histories. By using simple merger trees and semi-analytic models, which disregard feedback processes to exclusively identify merger effects on star formation histories, we examine the relation between various merger histories and SEDs of galaxies. From the results, we discuss whether the SED of a galaxy can represent and constrain its merger history.

• 천문학회보
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• 제38권1호
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• pp.32.1-32.1
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• 2013

We use numerical simulations to investigate the evolution of both the star formation rate (SFR) and the observable properties of equal-mass disk merger remnants for 18 different orbital configurations. In our analysis, the photometric properties of the remnants have been constructed by considering dust reddening effect in order to facilitate the comparison with observational data of large surveys such as the Sloan Digital Sky Survey (SDSS). First, we found that the detailed evolutions of merging galaxies are different between the merging characteristics such as merging time scale, SFR history, and burst efficiency. Around $70{\pm}5$ percent of gas turns into stars until the merger-induced starburst ends regardless of merger types. Our study also suggests that merger features involve a small fraction of stars. Merger features last roughly 3 times the final coalescence time of galaxy mergers. For a shallower surface brightness limit, the features seem to survive in a shorter time, which is the reason why detecting merger features by using shallow surveys were difficult in the past.

• 천문학논총
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• 제30권2호
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• pp.473-474
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• 2015

Halo merger trees are the essential backbone of semi-analytic models for galaxy formation and evolution. Srisawat et al. (2013) show that different tree building algorithms can build different halo merger histories from a numerical simulation for structure formation. In order to understand the differences induced by various tree building algorithms, we investigate the impact of halo merger trees on a semi-analytic model. We find that galaxy properties in our models show differences between trees when using a common parameter set. The models independently calibrated for each tree can reduce the discrepancies between global galaxy properties at z=0. Conversely, with regard to the evolutionary features of galaxies, the calibration slightly increases the differences between trees. Therefore, halo merger trees extracted from a common numerical simulation using different, but reliable, algorithms can result in different galaxy properties in the semi-analytic model. Considering the uncertainties in baryonic physics governing galaxy formation and evolution, however, these differences may not necessarily be significant.

• 천문학회보
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• 제44권2호
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• pp.39.2-39.2
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• 2019

Diffuse radio emissions at the outskirt of merging galaxy clusters called radio relics provide a unique channel to understand the merger history. We present a recent discovery of double radio relics in the cluster merger ZwCL1447+2619 from our recent Giant Metrewave Radio Telescope observations. Both Band 3 (300-500 MHz) and Band 4 (550-850 MHz) data reveal a large (~1Mpc) and thin (~40kpc) radio relic ~1Mpc from the cluster X-ray center and a small radio relic (~0.3 Mpc) on the opposite side. These remarkable radio data together with Subaru weak-lensing analysis and Chandra X-ray observations enable us to reconstruct the merger scenario. Our preliminary analysis suggests that the cluster ZwCL J1447+2619 is a post-merger near its returning phase. In addition, using Keck DEIMOS spectroscopy, we find many "green" and "blue" member galaxies are located between the radio relics, a possible indication of merger shock-driven star formation activities.

• 천문학회보
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• 제39권1호
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• pp.33.2-33.2
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• 2014

Halo merger trees are essential backbones of semi-analytic models for galaxy formation and evolution. Recent studies have pointed out that extracting merger trees from numerical simulations of structure formation is non-trivial; different algorithm can give differing merger histories. Thus they should be carefully understood before being used as input for models of galaxy formation. As one of the projects proposed in the SUSSING MERGER TREES Workshop, we investigate the impact of different halo merger trees on a semi-analytic model. We find that the z = 0 global galaxy properties in our model show differences between trees when using a common parameter set, but that these differences are not very significant. However, the star formation history of the Universe and the properties of satellite galaxies can show marked differences between trees with different methods for constructing a tree. Calibrating the SAM for each tree individually to the empirical data can reduce the discrepancies between the z = 0 global galaxy properties, however this is at cost of increasing the differences in evolutionary histories of galaxies. Furthermore, the underlying physics implied can vary, resulting in key quantities such as the supernova feedback efficiency differing by factors of 2. Such a change alters the regimes where star formation is primarily suppressed by supernovae. Therefore, halo merger trees extracted from a common halo catalogue using different, but reliable, algorithms can result in a difference in the semi-analytic model, however, given the enormous uncertainties in galaxy formation physics, these are not necessarily significant.

• 천문학회보
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• 제43권2호
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• pp.38.1-38.1
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• 2018

A merging galaxy cluster is a useful laboratory to study many interesting astrophysical processes such as intracluster medium heating, particle acceleration, and possibly dark matter self-interaction. However, without understanding the merger scenario of the system, interpretation of the observational data is severely limited. In this work, we focus on the off-axis binary cluster merger Abell 115, which possesses many remarkable features. The cluster has two cool cores in X-ray with disturbed morphologies and a single giant radio relic just north of the northern X-ray peak. In addition, there is a large discrepancy (almost a factor of 10) in mass estimate between weak lensing and dynamical analyses. To constrain the merger scenario, we perform a hydrodynamical simulation with the adaptive mesh refinement code RAMSES. We use the multi-wavelength observational data including X-ray, weak-lensing, radio, and optical spectroscopy to constrain the merger scenario. We present detailed comparisons between the simulation results and these multi-wavelength observations.

• The Journal of Asian Finance, Economics and Business
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• 제7권7호
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• pp.49-58
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• 2020

This paper examines the impact of mergers on the financial performance of the Jordanian banking sector. This paper applies the financial approaches in analysing the effects of mergers on Jordanian banks' performance for two the periods: four years pre-merger and four years' post-merger for the period from 2001 to 2009. The sample of the study solely contains the case of the merger of the Jordan Ahli Bank (AHLI bank) with Philadelphia Bank in 2005. Data are tested for normality using the Shapiro-Wilk Test and Kolmogorov Smirnov test. The financial ratios and a statistical technique as a Mann-Whitney U test were used to assess the significant differences in the financial performance of the selected banks pre- and post-merger by investigating the performance-related financial ratio groups that are expressed by leverage, liquidity, efficiency, and cash flow ratio. The results show that there is an insignificant improvement in the ratios of AHLI bank in the period after the merger, except for the superior result provided by this study indicating that the leverage ratios improved significantly. The reason for the insignificant improvement in financial ratios may be that the post-merger period corresponds to the period of the global financial crisis that began in 2007.

• 천문학회보
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• 제41권1호
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• pp.34.1-34.1
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• 2016

Galaxy clusters are the sites where the most massive galaxies are found, and so the most dramatic merger histories are embedded. Our deep (mu ~ 28 mag/arcsec^2) images of Abell 119 at z = 0.044 using the Blanco 4-m telescope at CTIO revealed post-merger signatures in ~35% of galaxies brighter than Mr < -19.5, suggesting that so many galaxies even in clusters have gone through galaxy mergers at recent epoch. We went further to understand the impact of mergers in cluster galaxies using stellar kinematics from the SAMI Integral Field Unit on the galaxies of Abell 119 in three aspects of kinematics : orientations, levels of rotation, and kinematic shapes. We found that 30% of the merger-featured galaxies show misalignment in the angle between the photometric major and the rotation axes, and most of them show complex kinematics. For comparison, only 5% of non-merger-featured galaxies show the misalignment. Moreover, our analysis using the Tully-Fisher relation shows that galaxy interactions can both enhance or reduce galaxy spin depending on the merger geometry. We present our preliminary result and discussion on the role of galaxy mergers in cluster environment from the perspective of kinematics.

• 천문학회보
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• 제44권2호
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• pp.77.1-77.1
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• 2019

We present the results of the merger fraction evolution for galaxies in NEP-Wide field depending on star formation mode and redshift. We select the galaxies which have AKARI 9 ㎛ detections as a sample for large number of galaxies. We use multi-wavelength data from GALEX to Herschel, and Subaru HSC i-band images for analysis. We classify the merger galaxies with using Gini and M20, which are non-parametric calculated by statmorph code. We obtain the total infrared luminosity from the SED modeling with using one band, AKARI 9 ㎛. We find that the merger fractions of galaxies in all different star formation mode increase as the redshift increases. However, with fixed mass range of 10.5 < log(M🞵) < 11.5, the merger fractions of starbursts significantly increase as the redshift increases compared to those of main sequence and quiescent galaxies. We discuss the implications of these results in this poster.

• 천문학회보
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• 제37권1호
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• pp.40.1-40.1
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• 2012

In the hierarchical universe, galaxy merger is predicted to be frequent, and thus it is an important element for understanding galaxy evolution. In particular, star formation is greatly enhanced during the merger. The aim of this study is to understand the position and rate change of star formation caused by equal-mass edge-on mergers. We use the GADGET2- N-body/SPH code, and fully consider gas cooling, star formation, and supernova feedback. We show the star formation rate (SFR), and the magnitude and color evolution of the merger remnants for 18 different configurations varying orbit elements and inclinations of host galaxies against orbit planes. Then we construct the mock images of the remnants and investigate on how equal-mass galaxy merger affects the SFR and color/magnitude evolution while considering dust reddening. We conclude that over 90% mass of SF in equal-mass merger is in the central region. SF in tidal feature involves a small fraction of new stars and thus is difficult to detect unless deep imaging is performed. Around 55 ${\pm}$ 5 percent of gas turns into stars until the final coalescence which typically corresponds to 0.8, 1.2, and 2.5 Gyr for direct, parabolic, and elliptical orbit, respectively. This result is roughly consistent with Cox et al. 2000. We plan to implement this result into semi-analytic model of galaxy formation. Caveats and future work on merging conditions are discussed.