• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.79.2-79.2
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• 2019

Based on three types of 2-point statistics (galaxy clustering, galaxy-galaxy lensing, and cosmic shear power spectra) from the Deep Lens Survey (DLS), we constrain cosmology and baryonic feedback. The DLS is a deep survey, so-called a precursor to LSST, reaching down to ~27th magnitude in BVRz' over 20 deg2. To measure the three power spectra, we choose two lens galaxy populations centered at z ~0.27 and 0.54 and two source galaxy populations centered at z ~0.64 and 1.1, with more than 1 million galaxies. We perform a number of consistency tests to confirm the reliability of the measurements. We calibrated photo-z estimation of the lens galaxies and validated the result with galaxy cross-correlation measurement. The B-mode signals, indicative of potential systematics, are found to be consistent with zero. The two cosmological results independently obtained from the cosmic shear and the galaxy clustering + galaxy-galaxy lensing measurements agree well with each other. Also, we verify that cosmological results between bright and faint sources are consistent. While there exist some weak lensing surveys showing a tension with Planck, the DLS constraint on S8 agrees nicely with the Planck result. Using the HMcode approach derived from the OWLS simulation, we constrain the strength of baryonic feedback. The DLS results hint at the possibility that the actual AGN feedback may be stronger than the one implemented in the current state-of-the-art simulations.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.59.4-59.4
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• 2019

In this talk, we will give an overview of the small telescope network project in Korea. The small telescope network is a project in planning that would gather 0.4m-1.0m telescopes in Korea together for a common use in research and education, and the project is being led by the Optical/IR Astronomy Division of KAS. Even in the era of giant telescopes, small telescopes are still competitive for various research topics that require rapid response or long-term, steady monitoring. There are quite a few small telescopes in Korea, but the research use of these telescope has been very limited. By organizing these telescopes together, the small telescope network hopes to bring these telescopes in full operation and offer Korean astronomers competitive observational resources. In this talk, we will outline the project, describe potential resources, and several science cases such as multi-messenger astronomy, supernovae, and AGN. We will also introduce how this project might be run, with the expected operation of the small network starting at 2020.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.39.1-39.1
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• 2020

We examine how the mass assembly of central galaxies depends on their location in the cosmic web. The HORIZON-AGN simulation is analysed at z~2 using the DISPERSE code to extract multi-scale cosmic filaments. We find that the dependency of galaxy properties on large-scale environment is mostly inherited from the (large-scale) environmental dependency of their host halo mass. When adopting a residual analysis that removes the host halo mass effect, we detect a direct and non-negligible influence of cosmic filaments. Proximity to filaments enhances the build-up of stellar mass, a result in agreement with previous studies. However, our multi-scale analysis also reveals that, at the edge of filaments, star formation is suppressed. In addition, we find clues for compaction of the stellar distribution at close proximity to filaments. We suggest that gas transfer from the outside to the inside of the haloes (where galaxies reside) becomes less efficient closer to filaments, due to high angular momentum supply at the vorticity-rich edge of filaments. This quenching mechanism may partly explain the larger fraction of passive galaxies in filaments, as inferred from observations at lower redshifts.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.257-261
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• 2017

We built a $8{\mu}m$ selected sample of galaxies in the NEP-AKARI field by defining 4 redshift bins with the four AKARI bands at 11, 15, 18 and 24 microns (0.15 < z < 0.49, 0.75 < z < 1.34, 1.34 < z < 1.7 and 1.7 < z < 2.05). Our sample contains 4079 sources, 599 are securely detected with Herschel/PACS. Also adding ultraviolet (UV) data from GALEX, we fit the spectral energy distributions using the physically motivated code CIGALE to extract the star formation rate, stellar mass, dust attenuation and the AGN contribution to the total infrared luminosity ($L_{IR}$). We discuss the impact of the adopted attenuation curve and that of the wavelength coverage to estimate these physical parameters. We focus on galaxies with a luminosity close the characteristic $L^*_{IR}$ in the different redshift bins to study the evolution with redshift of the dust attenuation in these galaxies.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.317-319
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• 2017

We propose a cosmological survey to probe star formation and nuclear activity in galaxies at redshifts of z=2-4 by polycyclic aromatic hydrocarbon (PAH) features using the SPICA mid-infrared instrument (SMI) with a spectral resolution of R=20. We will cover a wavelength range of $20-36{\mu}$ that corresponds to z=2-4 for the PAH features (11.3, 7.7, and $6.2{\mu}$). The sensitivity will be $1{\times}10^{-19}W/m^2(5{\sigma})$ in case of a reference survey that covers 4 arcmin2 field in a one-hour observation. It corresponds to $L_{IR}=2{\times}10^{11}L_{\odot}$ at z=3 and will give us more than 10000 galaxies in a 450 hour survey.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.281-285
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• 2017

We present a summary of our spectroscopic redshift catalogue of 404 sources in the AKARI Deep Field South (ADF-S). We have used the AAOmega spectrograph to target mid-infrared and far-infrared sources selected primarily from AKARI observations in this field for which we were able to obtain optical counterparts. Our sources with identified redshifts include 316 with $H{\alpha}$ detections at $z{\leq}0.345$ and 15 sources at z > 1 with MgII or $Ly{\alpha}$ emission lines. About 13% of our $z{\leq}0.345$ sources are dominated by active galactic nuclei (AGN) emission, although many show emission from both star formation and AGNs. The median Balmer decrement is 5.9. Ultra-luminous infrared galaxies (ULIRGs) were found only in the higher-redshift sources. Optical and near infrared data will be available shortly, enabling calibration of the line luminosities and spectral energy distribution (SED) fitting for these sources.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.213-217
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• 2017

The recent updates of the North Ecliptic Pole deep ($0.5deg^2$, NEP-Deep) multi-wavelength survey covering from X-ray to radio-wave is presented. The NEP-Deep provides us with several thousands of $15{\mu}m$ or $18{\mu}m$ selected galaxies, which is the largest sample ever made at these wavelengths. A continuous filter coverage in the mid-infrared wavelength (7, 9, 11, 15, 18, and 24 µm) is unique and vital to diagnose the contributions from starbursts and AGNs in the galaxies out to z=2. The new goal of the project is to resolve the nature of the cosmic star formation history at the violent epoch (e.g. z=1-2), and to find a clue to understand its decline from z=1 to present universe by utilizing the unique power of the multiwavelength survey. The progress in this context is briefly mentioned.

• International Journal of Industrial Entomology and Biomaterials
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• v.27 no.1
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• pp.185-202
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• 2013

In this study, we present the nearly complete mitogenome sequences of the garden chafer, Polyphylla laticollis manchurica, which is listed as an endangered species in Korea. The P. l. manchurica mitogenome, which includes unfinished whole A+T-rich region and a partial srRNA was 14,473-bp long, possessing typical sets of genes (13 PCGs, 22 tRNA genes, and 2 rRNA genes). Gene arrangement of the P. l. manchurica mitogenome was identical to the common one found in the majority of insects. The 5 bp-long motif sequence (TAGTA) that has been suggested to be the possible binding site for the transcription termination peptide for the major-strand was also found in the P. l. manchurica mitogenome between $tRNA^{Ser}$(UCN) and ND1. The start codon for COI gene and ATPase8 was designated as a typical TTG. All tRNAs of the P. l. manchurica showed a stable canonical clover-leaf structure of other mt tRNAs, except for $tRNA^{Ser}$(AGN), DHU arm of which could not form stable stemloop structure. As has been previously determined, the high A/T content was unanimously observed in P. l. manchurica in terms of A/T bias in the third codon position (73.5%) compared with the first (66.4%) and second codon position (66.2%). The PCGs encoded in major-strands are slightly T-skewed, whereas those of the minor-strand are A-skewed, indicating strand asymmetry in nucleotide composition in the Coleoptera including P. l. manchurica.

• Journal of The Korean Astronomical Society
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• v.48 no.5
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• pp.237-255
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• 2015

The Interferometric Monitoring of Gamma–ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma–ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non–optimal weather conditions.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.50.1-50.1
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• 2017

We present our study of the correlation between star formation rate(SFR) and merging activities of nearby galaxies(d<150Mpc). Our study uses 265 UV-selected galaxies which are not classified as AGN. The UV selection is made using the GALEX Atlas of Galaxies (Gil de Paz+07) and the updated UV catalog of nearby galaxies (Bai+15). We use deep R band optical images reaching to $1{\sigma}$ surface brightness detection limit ${\sim}27mag/arcsec^2$ to classify merger features by visual inspection. We also estimated unobscured SFR($SFR_{NUV}$) and obscured SFR($SFR_{W4}$) using Near-UV continuum and 22 micron Mid-IR luminosity respectively as a indicator of star forming activity. The fraction of galaxies with merger features in each SFR bin is obtained to see if how the fraction of galaxies with merging features($F_m$) changes as a function of SFR. As a result, for 203 late type galaxies(LTGs), we found that merger fraction increases from ~8% up to 50% with $SFR_{W4}$, while for 229 LTGs $SFR_{NUV}$ shows relatively consistent fraction(~18%) of merger fraction. For early type galaxies(ETGs), we could also find no significant correlation between $F_m$ and SFR(both $SFR_{NUV}$ and $SFR_{W4}$). This result suggests that a main driver of star forming activity of UV bright galaxies, especially for obscured late types, is mergers.