• 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.185-187
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• 2017

Combining the AKARI Point Source Catalog and the 37-month Monitor of All-sky X-ray Image (MAXI) catalog, the infrared and X-ray properties of nearby active galactic nuclei were investigated. The 37-month MAXI catalog tabulates 100 nearby Seyfert galaxies, 73 of which are categorized into Seyfert I galaxies. Among these Seyfert galaxies, 69 ones were found to have an AKARI infrared counterpart. For the Seyfert I galaxies in this sample, a well-known correlation was found between the infrared and X-ray luminosities. However, the observed X-ray luminosity of the Seyfert II galaxies tends to be lower for the infrared luminosity than the Seyfert I galaxies. This suggests that the X-ray absorption is significant in the Seyfert II galaxies. The Seyfert II galaxies seem to have a bimodal distribution of the IR color between $18{\mu}m$ and $90{\mu}m$. Especially, a large fraction of the Seyfert II galaxies exhibits a redder IR color than the Seyfert I galaxies. A possible origin of the redder IR color is briefly discussed, in relation to the star formation activity in the host galaxy, and to the X-ray absorption.

• Journal of The Korean Astronomical Society
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• v.44 no.5
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• pp.161-175
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• 2011

We examine the dependence of the morphology of spiral galaxies on the environment using the KIAS Value Added Galaxy Catalog (VAGC) which is derived from the Sloan Digital Sky Survey (SDSS) DR7. Our goal is to understand whether the local environment or global conditions dominate in determining the morphology of spiral galaxies. For the analysis, we conduct a morphological classification of galaxies in 20 X-ray selected Abell clusters up to z~0.06, using SDSS color images and the X-ray data from the Northern ROSAT All-Sky (NORAS) catalog. We analyze the distribution of arm classes along the clustercentric radius as well as that of Hubble types. To segregate the effect of local environment from the global environment, we compare the morphological distribution of galaxies in two X-lay luminosity groups, the low-$L_x$ clusters ($L_x$ < $0.15{\times}10^{44}$erg/s) and high-$L_x$ clusters ($L_x$ > $1.8{\times}10^{44}$erg/s). We find that the morphology-clustercentric relation prevails in the cluster environment although there is a brake near the cluster virial radius. The grand design arms comprise about 40% of the cluster spiral galaxies with a weak morphology-clustercentric radius relation for the arm classes, in the sense that flocculent galaxies tend to increase outward, regardless of the X-ray luminosity. From the cumulative radial distribution of cluster galaxies, we found that the low-$L_x$ clusters are fully virialized while the high-$L_x$ clusters are not.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.54.3-54.3
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• 2015

To probe the star formation in local and early Universe, the NISS with a capability of imaging spectroscopy in the near-infrared is being developed by KASI. The main scientific targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design of the NISS with 15cm aperture was optimized to obtain a wide field of view (FoV) of $2deg.{\times}2deg.$ as well as a wide spectral coverage from 0.9 to $3.8{\mu}m$. The opto-mechanical structure was designed to be safe enough to endure in both the launching condition and the space environment. The dewar will operate $1k{\times}1k$ infrared sensor at 80K stage. The NISS will be launched in 2017 and explore the large areal near-infrared sky up to $200deg.^2$ in order to get both spatial and spectral information for astronomical objects. As an extension of the NISS, KASI is planning to participate in a new small space mission together with NASA. The promising candidate, SPHEREx (Spectro-Photometer for the History of the Universe Epoch of Reionization, and Ices Explorer) is an all-sky survey satellite designed to reveal the origin of the Universe and water in the planetary systems and to explore the evolution of galaxies. Though the survey concept is similar to that of the NISS, the SPHEREx will perform the first near-infrared all-sky imaging spectroscopic survey with the wider spectral range from 0.7 to $5{\mu}m$ and the wider FoV of $3.5deg.{\times}7deg.$ Here, we report the current status of the NISS and introduce new mission for the near-infrared imaging spectroscopic survey.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.68.1-68.1
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• 2013

Infrared Medium-Deep Survey is a near-infrared imaging survey geared toward understanding the formation and the evolution of quasars and galaxies at high redshift, and studying transient and time-variable objects such as gamma-ray bursts, supernovae, and young stellar objects. The survey uses a multi-tier structure, with deep imaging survey of 100 $deg^2$ using UKIRT to the depth of 23 AB mag, and a shallower imaging of interesting sources using the CQUEAN camera on the 2.1m telescope at McDonald observatory. This talk will give an overview of the survey strategy, the instrument development, and science highlights. The science highlights will include the discovery of high redshift quasars, high redshift galaxy clusters, GRBs, and other interesting sources. At the end of the talk, we will also present the future prospects of our study.