• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.123-128
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• 2012

An overview of the North Ecliptic Pole (NEP) deep multi-wavelength survey covering from X-ray to radio wavelengths is presented. The main science objective of this multi-wavelength project is to unveil the star-formation and AGN activities obscured by dust in the violent epoch of the Universe (z=0.5-2), when the star formation and black-hole evolution activities were much stronger than the present. The NEP deep survey with AKARI/IRC consists of two survey projects: shallow wide (8.2 sq. deg, NEP-Wide) and the deep one (0.6 sq. deg, NEP-Deep). The NEP-Deep provides us with a $15{\mu}m$ or $18{\mu}m$ selected sample of several thousands of galaxies, the largest sample ever made at these wavelengths. A continuous filter coverage at mid-IR wavelengths (7, 9, 11, 15, 18, and $24{\mu}m$) is unique and vital to diagnose the contribution from starbursts and AGNs in the galaxies at the violent epoch. The recent updates of the ancillary data are also provided: optical/near-IR magnitudes (Subaru, CFHT), X-ray (Chandra), FUV/NUV (GALEX), radio (WSRT, GMRT), optical spectra (Keck/DEIMOS etc.), Subaru/FMOS, Herschel/SPIRE, and JCMT/SCUBA-2.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.74.2-74.2
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• 2017

Faint quasars are important to test the possibility that quasars are the main contributor to the cosmic reionization. However, it has been difficult to find faint quasars due to the lack of deep, wide-field imaging data. In this poster, we present our efforts to find faint quasars in the ELAIS-N1 field through the deep data (iAB ~ 25) obtained by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. To select reliable quasar candidate, we also use the near-infrared (NIR) data of the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS). Using multiple-band color cuts, we select high redshift quasar candidates. To confirm them as high redshift quasars, candidates are observed by the SED camera for QUasars in EArly uNiverse (SQUEAN) instrument in several medium band filters that can sample the redshifted Lyman break efficiency. The quasar sample will be used to study the growth of BH and stellar mass, the relation between the quasar activity and the host galaxy, and their contribution to the cosmic re-ionization.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.59.4-60
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• 2018

To investigate the impact of the high-redshift quasars on cosmic reionization, the faint end slope of the quasars luminosity function has to be determined precisely. More quasars with low luminosity are needed to constrain the contribution to reionization in the early universe. However, finding these quasars has been regarded as tough process owing to the improper shallow depth of imaging data. In recent days, the release data of Subaru Hyper Suprime-Cam (HSC) Strategic Program survey which provide the deep images reaching ~ 25 mag facilitates searching the faint quasars candidates. To find faint quasar candidates in ELAIS-N1 field, along with the HSC data, two near-infrared (NIR) data sets also be used : The Infrared Medium-deep Survey (IMS) and The UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS). Quasar candidates selected from the multi-band color cut were observed by the SED camera for QUasars in EArly uNiverse (SQUEAN) instrument. To trace the redshifted Lyman break efficiently, appropriate medium bands comparable to targeted redshift range are chosen. The most reliable quasar candidates are finally determined through SED fitting. Using this less luminous quasars candidates, we can speculate the relation between the quasar growth and the host galaxy unbiasedly and estimate the contribution to the cosmic reionization.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.36.2-36.2
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• 2018

Cosmic reionization era in the early universe was playing a leading part on making the present universe we know. However, we have not been able to reveal the main contributor to the cosmic reionization to date. Faint quasars have been mentioned as the alternative due to the uncertainty of the faint end slope of the quasars luminosity function. With the availability of the deep (~25mag) images from Subaru Hyper Suprime-Cam (HSC) Strategic Program survey, we have tried to find more quasar with low luminosity in the ELAIS-N1 field. Faint quasar candidates were selected from several multi-band color cut criteria based on the track of the simulated quasar at z ~ 5. The Infrared Medium-deep Survey (IMS) and The UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS) provide J band information which is used to cover the relatively long wavelength range of quasar spectra. To search the reliable candidates with possible Lyman break, medium-band observation was performed by the SED camera for QUasars in EArly uNiverse(SQUEAN) in the McDonald observatory and Seoul National University 4k Camera(SNUCAM) in the Maidanak observatory. Photometric redshifts of the observed candidates were estimated from chi-square minimization. Also, we predicted the importance of the faint quasar to the cosmic reionization from the expected number density of the faint quasar.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.42.1-42.1
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• 2015

Accurately estimating black hole (BH) masses at high redshifts is imperative in the current and future era of large-area extragalactic spectroscopic surveys. We present an extension of existing comparisons between rest-frame UV and optical virial BH mass estimators to intermediate redshifts, lower luminosities, and lower BH masses, comparable to the local $H{\beta}$ reverberation-mapping sample. We use data from the AGES survey and also newly acquired near-infrared spectra from the FMOS instrument on Subaru telescope for 89 broad-lined active galaxies at redshifts between 0.5 and 1.6. We focus on the MgII, CIV, and CIII broad emission lines and compare them to both $H{\alpha}$ and $H{\beta}$, using two different prescriptions to describe their emission profile width. We confirm that MgII shows a tight correlation with $H{\alpha}$, with a scatter of ~0.25 dex. The CIV and CIII estimators can be considered viable virial mass estimators, despite large scatter values. We combine our dataset with previous high redshift and high luminosity CIV and CIII measurements from the literature and we calculate a scatter of $\sim0.4$ dex and an offset to the 1:1 relation consistent with 0 for the combined sample. This updated comparison spans a total of 4 decades in BH mass, a much wider range than any previous individual study.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.181-182
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• 2012

Using the AKARI mid-infrared all-sky survey catalogue, we are searching for debris disks which are important objects as an observational clue to on-going planetary system formation. Debris disk candidates are selected through a significant excess of the measured flux over the predicted flux for the stellar photospheric emission at $18{\mu}m$. The fluxes were originally estimated based on the near-infrared spectral energy distributions (SEDs) of central stars constructed from the 2MASS J-, H-, and Ks-band fluxes. However, we found that in many cases the 2MASS photometry has large errors due to saturation in the central part of a star image. Therefore we performed follow-up observations with the IRSF 1.4m near-infrared telescope in South Africa to obtain accurate fluxes in the J-, H-, and Ks-bands. As a result, we have succeeded in improving the SEDs of the central stars. This improvement of the SEDs allows us to make more reliable selection of the candidates.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.313-315
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• 2017

We present physical properties of $24{\mu}m$ galaxies detected by AKARI and Spitzer and their evolution between redshifts 0.4 < z < 2. Using multi-wavelength data from X-ray to radio observations in NEP Deep Field (for AKARI) and Subaru/XMM-Newton Deep Field (for Spitzer), we derive photometric redshift, stellar mass, star-formation rate (SFR), dust extinction magnitude and rest-frame luminosities/colors of the $24{\mu}m$ galaxies from photometric SED fitting. We infer the SFRs from rest-frame ultraviolet luminosity and total infrared luminosity calibrated against Herschel photometric data. For both survey fields, we obtain complete samples with stellar mass of > $10^{10}M_{\odot}$ and SFR of > $30M_{\odot}/yr$ up to z = 2. We find that specific SFRs evolves with redshift at all stellar masses in NON-power-law galaxies (non-PLGs) as star-formation dominant luminous infrared galaxies (LIRGs). The correlations between specific SFR and stellar mass in the Spitzer and AKARI galaxy samples are well consistent with trends of the main sequence galaxies. We also discuss nature of PLGs and their evolution.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.169-173
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• 2017

We provide a new physical insight on the hot molecular clouds near the nucleus of the obscured AGNs. We performed near-infrared spectroscopic observations of heavily obscured AGNs in order to reveal physical characteristics of molecular clouds, especially focused on the CO fundamental ro-vibrational absorption around $4.7{\mu}m$. We have made systematic moderate-resolution spectroscopic observations toward 30 representative (U)LIRGs using the AKARI/IRC, and some of the ULIRGs showed the strong CO absorption feature. For three bright (U)LIRGs that show a steep red continuum with the deep CO absorption feature, IRAS 08572+3915, UGC 05101, and IRAS 01250+2832, we have also made high-resolution spectroscopic observations using the Subaru/IRCS. We have successfully detected many absorption lines up to highly excited rotational levels, and these lines are very deep and extremely broad. The derived physical conditions of molecular clouds are extreme; the gas temperature is as high as several 100 to a 1000 K, the $H_2$ column density is larger than $10^{22}cm^{-2}$, and the gas density is greater than $10^7cm^{-3}$. Such hot and dense molecular clouds must exist around the central engine of the AGN.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.57.1-57.1
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• 2012

We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy (gE) M86 in the Virgo galaxy cluster. Using the spectra obtained from the Multi-Object Spectroscopy (MOS) mode of Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope, we measured the radial velocities of 25 GCs, the metallicities of 16 GCs, and the ages of 8 GCs in M86. The mean velocity and the vocity dispersion of the GCs are < ${\upsilon}_p$ > = -354 ${\pm}$ 80 km/s and ${\sigma}_p$ = 292 ${\pm}$ 32km/s, respectively. The M86 GC system shows some rotation with a large uncertainty and the velocity dispersion of the blue GC system is 60 km/s larger than that of the red GC system. The mean metallicity and age of M86 GCs are <[Fe/H]> = -1.13 ${\pm}$ 0.47 and = 9.7 ${\pm}$ 4.0 Gyr, respectively. We found one GC younger than 5 Gyr. We discuss the spectroscopic results of the M86 GC system in comparison with the GC systems in other gEs.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.86.2-86.2
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• 2017

Blue stragglers (BSs) are the objects that are brighter and bluer than the stars at main-sequence turn-off point. In this study, we present the Ca-by and VI photometry for Galactic dwarf spheroidal galaxies using Subaru/Suprime-Cam and investigate the spatial distribution characteristics of BS stars using the hk index as a photometric metallicity indicator. We compare the cumulative radial distribution of the BS stars with those of two groups of red-giant-branch (RGB) stars divided by the hk-index strength, and find that the spatial distribution of all BS stars is closer to that of hk-weak (i.e. metal-poor) RGB stars. We also find that the hk-strong BS stars are more centrally concentrated than the hk-weak ones. We will discuss the use of hk-index as a metallicity indicator for the hot BS stars and suggest possible explanations for the results in terms of the origin of BS stars in the dwarf gal.