• 천문학회보
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• 제41권2호
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• pp.59.4-60
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• 2016

Recent galaxy simulations suggest several scenarios in which the inner structure of late-type galaxies (LTGs) is linked to global quenching. Exactly what mechanism governs the bulge quenching is, however, still under debate due to the lack of observational clues. In this study, we utilize a sample of ~1,300 LTGs in the local universe (0.02 < z < 0.2) from SDSS 7, and classify them into star-forming, AGN-hosting, and composite types and into barred and unbarred galaxies. We also examine each subgroup's specific star forming rate (sSFR), stellar mass and compactness using a data set matched with the advanced sSFR catalog by Chang et al. (2015). We find that while star-forming and composite galaxies show no detectable difference between barred and unbarred galaxies, barred AGNs have much lower sSFR than unbarred AGNs at given stellar mass and compactness, Such tendency is stronger for more massive and/or more concentrated galaxies. The results indicate that most AGN-driven quenching is triggered by growth of the bar structure, consistent with the previous simulations of bars.

• 천문학회보
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• 제42권2호
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• pp.78.3-78.3
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• 2017

The positions of galaxies in comoving Cartesian space varies under different cosmological parameter choices, inducing a redshift-dependent scaling in the galaxy distribution. The shape of the two-point correlation of galaxies exhibits a significant redshift evolution when the galaxy sample is analyzed under a cosmology differing from the true, simulated one. In our previous works, we can made use of this geometrical distortion to constrain the values of cosmological parameters governing the expansion history of the universe. This current work is a continuation of our previous works as a strategy to constrain cosmological parameters using redshift-invariant physical quantities. We now aim to understand the redshift evolution of the full shape of the small scale, anisotropic galaxy clustering and give a firmer theoretical footing to our previous works.

• 천문학회보
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• 제37권2호
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• pp.87.1-87.1
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• 2012

The fraction of blue galaxies in clusters is found to dramatically increase with redshift. This trend has been known as the Butcher-Oemler (B-O) effect which implies a significant evolution among the cluster galaxy population with time. It has been proposed that the blue galaxies in B-O clusters are at their last stage of star formation, probably using up the gas, which then might have evolved into red and passive cluster galaxies as found in the Local Universe. To test this hypothesis and ultimately to understand the evolution of cluster galaxy population as a function of redshift, we have embarked a multi-wavelength study of two carefully selected galaxy clusters at z~0.2 where the B-O effect becomes first noticeable. In this talk, I will introduce the Blind Ultra-deep Distant HI Environmental Survey (BUDHIES) on those two clusters and relevant multi-wavelength observations. Also, I will present the preliminary results of our recent Nobeyama CO observations of two galaxies selected among the BUHDIES sample.

• 천문학회보
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• 제46권1호
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• pp.53.2-53.2
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• 2021

Quasar luminosity function (QLF) shows the active galactic nucleus (AGN) demography as a result of the combination of the growth and the evolution of black holes, galaxies, and dark matter halos along the cosmic time. The recent wide and deep surveys have improved the census of high-redshift quasars, making it possible to construct reliable ultraviolet (UV) QLFs at 2 < z < 6 down to M1450 = -23 mag. By parameterizing these up-to-date observed UV QLFs that are the most extensive in both luminosity and survey area coverage at a given redshift, we show that the UV QLF has a universal shape, and their evolution can be approximated by a pure density evolution (PDE). In order to explain the observed QLF, we construct a model QLF employing the halo mass function, a number of empirical scaling relations, and the Eddington ratio distribution. We also include the outshining of AGN over its host galaxy, which made it possible to reproduce a moderately flat shape of the faint end of the observed QLF (slope of ~ -1.1). This model successfully explains the observed PDE behavior of UV QLF at z > 2, meaning that the QLF evolution at high redshift can be understood under the framework of halo mass function evolution. The importance of the outshining effect in our model also implies that there could be a hidden population of faint AGNs (M1450 > -24 mag), which are buried under their host galaxy light.

• 천문학회지
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• 제46권4호
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• pp.173-181
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• 2013

We trace the dynamical evolution of dark matter (DM) content in NGC 6397, one of the native Galactic globular clusters (GCs). The relatively strong tidal field (Galactocentric radius of ~ 6 kpc) and short relaxation timescale (~0.3 Gyr) of the cluster can cause a significant amount of DM particles to evaporate from the cluster in the Hubble time. Thus, the cluster can initially contain a non-negligible amount of DM. Using the most advanced Fokker-Planck (FP) method, we calculate the dynamical evolution of GCs for numerous initial conditions to determine the maximum initial DM content in NGC 6397 that matches the present-day brightness and velocity dispersion profiles of the cluster. We find that the maximum allowed initial DM mass is slightly less than the initial stellar mass in the cluster. Our findings imply that NGC 6397 did not initially contain a significant amount of DM, and is similar to that of NGC 2419, the remotest and the most massive Galactic GC.

• 천문학회보
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• 제38권2호
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• pp.38.1-38.1
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• 2013

We present the Yonsei evolutionary population synthesis (YEPS) models based on the high-resolution empirical spectral energy distributions (SEDs). We have adopted the MILES library in the optical wavelength, and our new models based on the MILES library show good agreements with our previous models presented in the YEPS I. The effect of hot horizontal-branch (HB) stars on the integrated properties of simple stellar populations (SSPs) is again confirmed by our models based on empirical SEDs. In addition, we have extended our empirical models to the near-IR wavelength and predicted the strengths of the calcium II triplet (CaT) and the Paschen triplet (PaT) based on the INDO-US and the Cenarro library. We find that the effect of HB stars and the age of SSPs on the CaT is almost negligible. On the other hands, the PaT models are very sensitive to the existence of hot stars, e.g., HB stars and young turn-off stars, and show very similar results with Balmer lines. Interestingly, the CaT distribution of GCs in NGC 1407, which is at odds with the optical (B-I) color distribution, can be explained by the unique feature of the CaT-[Fe/H] relations that show almost the same equivalent widths in the metal-rich regime. We will also discuss the impact of the second-generation populations on the strength of the CaT.

• 천문학회지
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• 제24권1호
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• pp.25-53
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• 1991

The evolution of the Galaxy is examined by the halo-disk model, using the time-dependent bimodal IMF and contraints such as cumulative metallicity distribution, differential metallicity distribution and PDMF of main sequence stars. The time scale of the Galactic halo formation is about 3Gyr during which the most of halo stars and metal abundance are formed and ${\sim}95%$ of the initial halo mass falls to the disk. The G-dwarf problem could be explained by the time-dependent bimodal IMF which is suppressed for low mass stars at the early phase (t < 1Gyr) of the disk evolution. However, the importance of this problem is much weakened by the Pagel's differential metallicity distribution which leads to less initial metal enrichment and many long-lived metal-poor stars with Z < $1/3Z_{\odot}$ The observational distribution of abundance ratios of C, N, O elements with respect to [Fe/H] could be reproduced by the halo-disk model, including the contribution of iron product by SNIs of intermediate mass stars. The initial enrichment of elements in the disk could be explained by the halo-disk model, resulting in the slight decrease and then the increase in the slopes of the [N/Fe]- and [C/Fe]-distributions with increasing [Fe/H] in the range of [Fe/H] < -1.

• 천문학회보
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• 제39권2호
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• pp.69.2-69.2
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• 2014

We present space-based near-IR (NIR) and optical photometry of globular clusters (GCs) of 16 early-type galaxies in the Fornax and Virgo Clusters. The NIR imaging data for the nearby galaxies was acquired with the IR Channel of the Wide Field Camera 3 (WFC3/IR) in the F110W ($J_{110}$) and F160W ($H_{160}$) bandpasses. We introduce the full sample of our WFC3/IR program, describe data reductions and photometric measurements including GC candidate selection criteria, and then show selected GCs' color-magnitude diagrams. The tilted features in the diagrams related to the morphological types of host galaxies are discussed in the context of galaxy formation and evolution histories. Combining F475W ($g_{475}$) and F850LP ($z_{850}$) data taken from the Advanced Camera for Surveys Virgo and Fornax Cluster Surveys with our NIR data, we investigate the bimodality in optical-NIR color distribution and the nonlinear feature of the optical-NIR color relation as a function of optical color for these extragalactic GC systems.

• 천문학회보
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• 제42권2호
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• pp.54.1-54.1
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• 2017

Intrinsic alignments (IA), the coherent alignment of intrinsic galaxy orientations, can be a source of a systematic error of weak lensing surveys. The redshift evolution of IA also contains information about the physics of galaxy formation and evolution. We present the first measurement of IA at high redshift, z~1.4, using the spectroscopic catalog of blue star-forming galaxies of the FastSound redshift survey, with the galaxy shape information from the Canada-Hawaii-France telescope lensing survey. The IA signal is consistent with zero with power-law amplitudes fitted to the projected correlation functions for density-shape and shape-shape correlation components, $A_{\delta+}=-0.0040\pm 0.0754$ and $A_{++}=-0.0159\pm 0.0271$, respectively. These results are consistent with those obtained from blue galaxies at lower redshifts (e.g., $A_{\delta+}=0.0035_{-0.0389}^{+0.0387}$ and $A_{++}=0.0045_{-0.0168}^{+0.0166}$ at z=0.51 from the WiggleZ survey), suggesting no strong redshift evolution of IA. The upper limit of the constrained IA amplitude corresponds to a few percent contamination to the weak-lensing shear power spectrum, resulting in systematic uncertainties on the cosmological parameter estimations by $-0.035<\Delta \sigma_8<0.026$ and $-0.025<\Delta \Omega_{\mathrm m}<0.019$.

• 천문학회보
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• 제42권1호
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• pp.42.2-42.2
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• 2017

We performed low-resolution spectroscopy for the red giant stars in the Galactic globular cluster (GC) NGC 5286, which is known to show intrinsic heavy element variations. We found that these stars are clearly divided into two subpopulations by CN index. These two subpopulations also show significant differences in the HK'and CH indices, where the CN-strong stars are more enhanced in both indices. From the comparison with high-resolution spectroscopic data of Marino et al. (2015), we found that the CN- and HK'-strong stars are also increased in the abundances of s-process elements and Fe. It appears that, therefore, these stars are later generation stars probably affected by supernova enrichment. In addition, NGC 5286 shows the CN-CH positive correlation among the whole sample, which is only discovered in the GCs with heavy element variations such as M22 and NGC 6273. Therefore, these results strengthen our previous suggestion that the CN-CH positive correlation may be associated with the heavy element variations in the GCs.