• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.54-54
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• 2014

We use dense redshift surveys of nine galaxy clusters at z ~ 0.2 to compare the galaxy distribution in each system with the projected matter distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts and the data in the literature, we construct spectroscopic samples within the region of weak-lensing maps of high (70-89%) and uniform completeness. With these dense redshift surveys, we construct galaxy number density maps using several galaxy subsamples. The shape of the main cluster concentration in the weak-lensing maps is similar to the global morphology of the number density maps based on cluster members alone, mainly dominated by red members. We cross correlate the galaxy number density maps with the weak-lensing maps. The cross correlation signal when we include foreground and background galaxies at 0.5zcl < z < 2 zcl is 10 - 23% larger than for cluster members alone at the cluster virial radius. The excess can be as high as 30% depending on the cluster. Cross correlating the galaxy number density and weak-lensing maps suggests that superimposed structures close to the cluster in redshift space contribute more significantly to the excess cross correlation signal than unrelated large-scale structure along the line of sight. Interestingly, the weak-lensing mass profiles are not well constrained for the clusters with the largest cross correlation signal excesses (>20% for A383, A689 and A750). The fractional excess in the cross correlation signal including foreground and background structures could be a useful proxy for assessing the reliability of weak-lensing cluster mass estimates.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.63.2-63.2
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• 2011

We describe the Infrared Medium-deep Survey (IMS), a survey of quasars in the early universe beyond z=5. IMS uses multi-wavelength archival data such as SDSS, CFHT-LS, UKIDSS, and SWIRE, which provide deep images over wide area enough for searching of high redshift bright quasars. In addition, we are carrying out J-band imaging survey with the depth of 23AB at UKIRT for up to 200 $deg^2$, of which 50 $deg^2$ is covered so far. For the quasar candidates at z~5.5, we are making observations with custom-made filters, which are more efficient to make robust quasar candidate samples in this redshift range. Because of the deeper survey depth and the unique methods, our IMS can provide a large number of high redshift quasars comparing with ongoing high redshift bright quasar survey. The high redshift quasars we confirm will give us with clues of the growth of super massive black holes and the metal enrichment history in the early universe.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.38.2-38.2
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• 2016

The mapping of dark matter clustering from real to redshift spaces introduces the anisotropic property to the measured density power spectrum in redshift space, known as the Redshift Space Distortion (hereafter RSD) effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to the indefinite cross correlations between the density and velocity fields, and the Finger-of-God (hereafter FoG) effect due to the randomness of the peculiar velocity field. Furthermore, the rigorous test of this mapping formula is contaminated by the unknown non-linearity of the density and velocity fields, including their auto- and cross-correlations, for calculating which our theoretical calculation breaks down beyond some scales. Whilst the full higher order polynomials remains unknown, the other systematics can be controlled consistently within the same order truncation in the expansion of the mapping formula, as shown in this paper. The systematic due to the unknown non-linear density and velocity fields is removed by separately measuring all terms in the expansion using simulations. The uncertainty caused by the velocity randomness is controlled by splitting the FoG term into two pieces, 1) the non-local FoG term being independent of the separation vector between two different points, and 2) the local FoG term appearing as an indefinite polynomials which is expanded in the same order as all other perturbative polynomials. Using 100 realizations of simulations, we find that the best fitted non-local FoG function is Gaussian, with only one scale-independent free parameter, and that our new mapping formulation accurately reproduces the observed power spectrum in redshift space at the smallest scales by far, up to k ~ 0.3 h/Mpc, considering the resolution of future experiments.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.267-269
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• 2017

We report the results of a multi-wavelength study in the North Ecliptic Pole (NEP) deep field and examine the far infrared-radio correlation (FIRC) for high and low redshift objects. We have found a correlation between the GMRT data at 610 MHz and the Herschel data at $250{\mu}m$ that has been used to define a spectral index. This spectral index shows no evolution against redshift. As a result of the study, we show a radio colour-infrared diagram that can be used as a redshift indicator.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.59.1-59.1
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• 2014

AGN feedback has been believed as playing an important role in the galaxy-super massive black hole (SMBH) co-evolution. AGN gas outflow can lead to AGN feedback. We investigate gas outflow of low-redshift AGNs by using blue shift/asymmetric index (BAI), and velocity offset of CIV line. By comparing these gas outflow indicators (BAI and velocity offset) to AGN properties (i.e., SMBH mass, bolometric luminosity, and Eddington ratio) and BLR gas metallicity, we find positive correlations among outflow, Eddington ratio, and metallicity. These relations are consistent with those observed at high-redshift. We discuss the possibility of the connection between previous star formation with current AGN accretion and outflow.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.36.1-36.1
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• 2012

Recent wide and deep surveys allow us to investigate the large scale structure of the Universe at high redshift. We present studies of the clustering of high redshift galaxies, using reprocessed UKIDSS DXS catalogue. We measure the angular correlation function of high redshift galaxies which is Extremely Red Objects (EROs). Firstly we found that their angular correlation functions can be described by a broken power-law. We also found that red or bright samples are more strongly clustered than those having the opposite characteristics, and that old, passive EROs are found to be more clustered than dustry, star-forming EROs. Additionally the average halo mass and other properties were estimated using the halo model. Finally the observed clustering of EROs was compared with predictions from the cosmological simulation.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.78.2-78.2
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• 2010

Ionization of hydrogen occurs globally in our universe. The epoch of this cosmic reionization may be probed by various observations, among which the 21cm observation of neutral hydrogen at high redshift is the most promising candidate. In order to provide a mock data, we have performed the first, self-consistent simulation of cosmic reionization. We account for all possible UV-radiating sources which reside in halos ranging from minihalos to atomically-cooling halos. In order to simulate the contribution from Pop III objects, we also calculate the radiative transfer of Lyman-Werner radiation and apply a suppression criterion for Pop III objects. Our priliminary result indicates that Pop III objects ionize the universe at very high redshift and create rich, small-scale bubble structure, while sources in atomically-cooling halos ionize the universe at relatively low redshift and create large-scale bubble structure. We discuss how these two different scales and epoch may be probed by future 21cm observations.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.36.1-36.1
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• 2010

The Redshift Search Receiver (RSR) is a sensitive, ultra-wideband spectrometer that is being built at the University of Massachusetts as one of the facility instruments for the 50-m Large Millimeter Telescope (LMT). It consists of four receivers each covering the entire 3 mm window from 74 to 111 GHz instantaneously. The primary goal of the receiver is to detect multiple molecular lines in galaxies at any distance and uniquely determine the redshift, in particular dust-obscured star forming systems at high-z which are not easily accessible. I will present some results from commissioning of the RSR on the Five College Radio Astronomy Observatory 14-m telescope, and discuss the future of the receiver.

• Journal of The Korean Astronomical Society
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• v.46 no.3
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• pp.97-102
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• 2013

In the present work, we prove the validity of two theorems on null-paths in a version of absolute parallelismgeometry. A version of these theorems has been originally established and proved by Kermak, McCrea and Whittaker (KMW) in the context of Riemannian geometry. The importance of such theorems lies in their applications to derive a general formula for the redshift of spectral lines coming from distant objects. The formula derived in the present work can be applied to both cosmological and astrophysical redshifts. It takes into account the shifts resulting from gravitation, different motions of the source of photons, spin of the moving particle (photons) and the direction of the line of sight. It is shown that this formula cannot be derived in the context of Riemannian geometry, but it can be reduced to a formula given by KMW under certain conditions.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.58.1-58.1
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• 2018

The redshift range $1.4{\lesssim}z{\lesssim}2.5$ is often called the 'redshift desert' because of the difficulties in measuring spectroscopic redshifts due to the shifting of the major spectroscopic features into near-infrared wavelength (Steidel et al. 2004). One of the most efficient and fast way to select galaxies at this redshift range is the BzK technique designed by Daddi et al. (2004). Combining deep BVRz data from Deep Lens Survey with the wide-field (~4.08 deg2) K-band image, we select 1200 star-forming BzKs (sBzKs) and 120 passive BzKs (pBzKs) at K < 21.25. We discuss about the photometric redshifts, star formation rates, and stellar mass of the selected BzKs. Possible large scale structure at $1.4{\lesssim}z$ < 1.6 based on the spatial distribution of the BzKs is also introduced.